Associations between physical fitness and adherence to the Mediterranean diet with health-related quality of life in adolescents: results from the LabMed Physical Activity Study

Associations between physical fitness and adherence to the Mediterranean diet with health-related... Abstract Background Physical fitness (PF) and adherence to the Mediterranean diet are important indicators of healthy lifestyles. The purpose of this study is to analyze the independent and combined associations between PF and adherence to Mediterranean diet with health-related quality of life (HRQoL) in adolescents. Methods This is a cross-sectional analysis with 956 Portuguese adolescents aged 12–18 years. HRQoL was measured with the Kidscreen-10 questionnaire. PF was assessed with the ALPHA health-related fitness battery. The 20-m shuttle run test was used for the estimation of cardiorespiratory fitness; handgrip strength and standing long jump tests were applied for the assessment of muscular fitness and the 4 × 10 m shuttle run test for the assessment of motor fitness (speed and agility). The results of the PF tests (cardiorespiratory fitness, muscular fitness and motor fitness) were transformed into standardized values (Z-scores) by age and sex. Adherence to the Mediterranean diet was assessed with the KIDMED index. Regression analysis and analysis of covariance were performed. Results PF (B = 0.228; P < 0.05) and adherence to the Mediterranean diet (B = 0.259; P < 0.05) were positively associated with HRQoL, after controlling for several variables. Participants classified as high PF and high adherence to Mediterranean diet had on average the highest HRQoL score compared with those with low PF and low adherence to Mediterranean diet (F(3, 939) = 4.270; P = 0.005), after adjustments for potential confounders. Conclusions The combination of high PF levels and optimal adherence to Mediterranean diet is positively associated with HRQoL. Introduction Health-related quality of life (HRQoL) is a multidimensional construct that relates to a person’s self-perceived health and consists of ratings of well-being and functionality, including physical well-being/functioning, emotional well-being, self-esteem, social functioning and family relations.1 During adolescence, several biological, physical, cognitive, psychological, social and emotional factors can affect one’s HRQoL and well-being.2 Physical fitness (PF) has been associated with health benefits in young people3 and is considered a marker of a healthy lifestyle, as well as a predictor of morbidity and mortality from cardiovascular disease and other causes.4 Previous data from Portuguese adolescents from the Health Behaviour in School-Aged Children (HBSC) study showed that self-reported fitness levels were positively associated with HRQoL.5 Likewise, three other studies indicated that both cardiorespiratory fitness and muscular fitness were positively associated with HRQoL in schoolchildren aged 8–11 years.6–8 The Mediterranean diet is considered one of the healthiest dietary patterns.9 Indeed, several studies have shown that greater adherence to a Mediterranean-like dietary pattern is associated with an improved health status10 with beneficial effects on arterial stiffness11; academic performance12 and the intensity of physical activity behaviour.13 However, recent data indicates that adherence to this dietary pattern is decreasing in Mediterranean regions, particularly among children and adolescents.14 Some recent studies have investigated the associations between Mediterranean diet and HRQoL in adolescents15,16 and reported positive associations between HRQoL and adherence to Mediterranean diet in youth. However, few studies have addressed the relationship between overall PF and Mediterranean diet with HRQoL in adolescents. Therefore, the aim of this study was to examine the independent combined associations between PF and adherence to the Mediterranean diet with HRQoL in adolescents. Methods Study design and sample The current report is part of the ‘Longitudinal Analysis of Biomarkers and Environmental Determinants of Physical Activity (LabMed Physical Activity Study)’, a school-based prospective cohort study carried out in five Portuguese cities from the Northern Region. The full description of the study protocol and measures can be seen in detail elsewhere.17 Briefly, baseline data was collected in the fall of 2011, for all students that agreed to participate in the study (n = 1229; aged 12–18 years). From this initial total sample, 956 adolescents (446 girls and 510 boys) had provided complete data on the variables of interest of the present report and therefore were included in this study. The study was conducted in accordance with the Portuguese Data Protection Authority (#1112434/2011), and the Portuguese Ministry of Science and Education (0246200001/2011) and the Faculty of Sports of University of Porto approved the study. All participants were informed of the study’s goals, and written informed consent was obtained from participating adolescents as well as from their parents or tutors. Measurements Health-related quality of life HRQoL was assessed by Kidscreen-10 questionnaire. It contains 10 items regarding family life, peers and school life. Kidscreen-10 is a one-dimensional measure that represents a global score adequate for use in large epidemiological surveys.18 Physical fitness PF was assessed following the protocols of the ALPHA health-related fitness battery.3 Participants performed the following tests: 20-m shuttle run test to estimate cardiorespiratory fitness; handgrip strength and standing long jump tests for the assessment of muscular fitness and, the 4 × 10 m shuttle run test to assess motor fitness (speed and agility). For the 20-m shuttle run test the participants were required to run in a straight line, between two lines distanced 20-m apart, while keeping pace with a pre-recorded audio CD. The initial speed was 8.5 km.h−1, which was increased by 0.5 km.h−1 each minute (1 min = one stage). The test was finished when the adolescent failed to reach the end lines before the audio signal on two occasions. The number of shuttles was recorded. Upper body isometric strength was assessed using a handgrip dynamometer, (T.K.K. 5001, Grip-A produced by Takei, Japan), adjusted by sex and hand size of each adolescent using the equations specifically developed for adolescents.19 Participants were instructed to stand with their arms by their side, fully extended, squeezing the handgrip continuously for at least 2 s, performing the test with the right and left hands in turn. A rest period of 90-s was given between trials. The test was performed twice and the best score recorded for each hand was used for analysis. The handgrip score (in kg) was calculated as the average of the left and right best scores and then was expressed in kilograms of body mass.20 In the standing long jump test (lower body explosive strength), the adolescents were instructed to jump, from the starting line and to push off vigorously and jump as far forward as possible landing on both feet and staying upright. The test was performed twice and the best distance was recorded in centimeters for analysis. The distance between the first heel-mark and the take-off line determined the standing jump score.3 For motor fitness, the participants were asked to run 4 × 10 m (back and forth), as fast as possible. Two parallel lines were drawn on the floor 10-m apart. In the start line, there was one sponge (B) and in the opposite line there were two sponges (A, C). When the start was given, the participant (without sponge) ran as fast as possible to the other line and returned to the starting line with the sponge (A), crossing both lines with both feet, then sponge (A) was changed by the sponge B in the starting line. Afterwards, the participant went back running as fast as possible to the opposite line and changed the sponge B by the C, and then ran back to the starting line. The test was performed twice and the best score was recorded in seconds for analysis. Lower scores indicate better performance. The results of the PF tests (cardiorespiratory fitness, muscular fitness and motor fitness) were transformed into standardized values (Z-scores) by age and sex. The Z-score of motor fitness was multiplied by −1, because a lower score indicates better performance. Then, the sum of the Z-Scores of tests was used to create the PF score. High PF score was considered when the participant had ≥1 SD of this Z-score. Adherence to Mediterranean diet Participants self-reported their dietary intake with the KIDMED index (Mediterranean Diet Quality Index for children and adolescents) developed by Serra-Majem et al.21 The final scores of the KIDMED index vary between 0 and 12 points, with higher scores indicating higher adherence to the Mediterranean diet. Participants were classified into three categories: (i) ≥8, optimal Mediterranean diet; (ii) 4–7, improvement is needed to adjust intake to Mediterranean patterns and (iii) ≤3, very low diet quality as proposed by Kontogianni.22 Body mass and height Anthropometric measurements were performed according to standard procedures. Body mass and height were measured using a portable electronic weight scale (Tanita Inner Scan BC 532, Tokyo, Japan) and a portable stadiometer (Seca 213, Hamburg, Germany), respectively, with the participant barefoot, wearing light clothing. Body mass index (BMI) was calculated as body mass divided by stature squared (kg/m2). Pubertal stage Adolescents self-reported their pubertal stage (from 1 to 5) relatively the secondary sex characteristics, according to the criteria of Tanner and Whitehouse.23 Girls were assessed by the stage of breast development (Tanner A) and public hair distribution (Tanner B), and boys by the stage of genitalia development (penis size and testicular volume—Tanner A) and pubic hair distribution (Tanner B). Socioeconomic status Adolescents’ socioeconomic status was assessed using the Family Affluence Scale,24 a four-item questionnaire where the participants report whether their family owns a car, whether they have his/her own bedroom, the number of family vacations during the last 12 months and the number of computers that the family owns. The items are summed to give a final socioeconomic index ranging from 0 to 9 points, with higher scores indicating higher socioeconomic status. Sleep duration Habitual sleep duration was self-reported, using the HBSC questionnaire. Adolescents were asked what time they usually woke up in the morning and what time they usually went to bed at night on a typical school day and on a typical weekend day. Average sleep duration per night was calculated as follows: 5 × sleep duration on weekdays plus 2 × sleep duration on weekend days. Statistical analysis Descriptive data are presented as means and standard deviations for continuous variables and in the case of the categorical variables as frequencies and percentages. To assess differences between sexes, the independent student’s t-test was used for the continuous variables and chi-square test for the categorical variables. Linear regression models were performed to determine the associations between PF and Mediterranean diet score (as predictors—independent and combined) and HRQoL (as dependent variable), adjusted for age, sex, pubertal stage, socioeconomic status, sleep duration and BMI. Unstandardized regression coefficients were used to express the B coefficients of the regression analyses. Analysis of covariance (ANCOVA) with Bonferroni post hoc multiple comparison tests were used to assess the differences between mean values of HRQoL across groups of PF (low and high) and adherence to Mediterranean diet: low (the first two categories collapsed ‘improvement is needed’ and ‘very low quality diet’) and high (‘optimal Mediterranean diet’). Covariates included were age, sex, pubertal stage, socioeconomic status, sleep duration and BMI. Data analyses were performed with the statistical software Statistical Package for Social Sciences (Windows version 24.0; SPSS Inc., Chicago, IL, USA). A P values < 0.05 was considered to indicate statistical significance. Results Table 1 shows the descriptive characteristics of the participants. Boys outperformed girls in all PF tests (P < 0.001 for all), while girls reported a significantly higher optimal adherence to the Mediterranean diet (P = 0.020) than boys. Table 1 Descriptive characteristics of the participants by sex   Total (n = 956)a  Girls (n = 446)a  Boys (n = 510)a  P*  Age (year)  14.5 (1.8)  14.3 (1.7)  14.6 (1.9)  0.003  Body mass (kg)  55.9 (12.8)  53.6 (10.9)  57.9 (13.9)  <0.001  Height (cm)  1.61 (0.10)  1.58 (0.07)  1.64 (0.1)  <0.001  BMI (kg/m2)  21.1 (3.8)  21.1 (3.7)  21.1 (3.9)  0.882  Pubertal stage A (I/II–V) (%)  7.4/30.5/48.1/14  4/30.2/51.5/14.3  10.4/30.7/45.2/13.7  0.004  Pubertal stage B (I/II–V) (%)  5.9/21.3/52.2/20.5  2.7/23.3/51/23  8.7/19.7/53.3/18.3  0.001  Long jump (cm)  161 (33)  141.4 (24.1)  177.6 (30.3)  <0.001  Handgrip (kg)  27.8 (8.6)  23.3 (4.8)  31.7 (9.2)  <0.001  Handgrip/body mass (kg)  0.50 (0.1)  0.44 (0.09)  0.55 (0.12)  <0.001  Cardiorespiratory fitness (number of shuttles)  45.9 (25.9)  30.7 (14.9)  58.9 (26.2)  <0.001  Motor fitness (s)  11.7 (1.3)  12.4 (1.2)  11.1 (1.1)  <0.001  PF score  −0.0088 (2.9)  −0.52 (2.9)  0.44 (1.8)  <0.001  Mediterranean diet (KIDMED index)  7.1 (2.1)  7.3 (1.8)  7.0 (3.1)  0.086      Very low diet quality (≤3) (%)  6.4  4  8.4        Improvement is needed (4–7) (%)  52.8  53.2  52.4  0.020      Optimal Mediterranean diet (≥8) (%)  40.8  42.8  39.2    Socioeconomic status  6.4 (1.6)  6.4 (1.6)  6.3 (1.6)  0.011  Sleep duration average (h)  8.6 (0.9)  8.5 (0.9)  8.6 (0.9)  0.071  Sleep duration on weekends (h)  9.6 (1.6)  10.0 (1.4)  9.3 (1.6)  <0.001  HRQoL (Kidscreeen-10)  39.1 (5.6)  38.6 (5.7)  39.5 (5.4)  0.009    Total (n = 956)a  Girls (n = 446)a  Boys (n = 510)a  P*  Age (year)  14.5 (1.8)  14.3 (1.7)  14.6 (1.9)  0.003  Body mass (kg)  55.9 (12.8)  53.6 (10.9)  57.9 (13.9)  <0.001  Height (cm)  1.61 (0.10)  1.58 (0.07)  1.64 (0.1)  <0.001  BMI (kg/m2)  21.1 (3.8)  21.1 (3.7)  21.1 (3.9)  0.882  Pubertal stage A (I/II–V) (%)  7.4/30.5/48.1/14  4/30.2/51.5/14.3  10.4/30.7/45.2/13.7  0.004  Pubertal stage B (I/II–V) (%)  5.9/21.3/52.2/20.5  2.7/23.3/51/23  8.7/19.7/53.3/18.3  0.001  Long jump (cm)  161 (33)  141.4 (24.1)  177.6 (30.3)  <0.001  Handgrip (kg)  27.8 (8.6)  23.3 (4.8)  31.7 (9.2)  <0.001  Handgrip/body mass (kg)  0.50 (0.1)  0.44 (0.09)  0.55 (0.12)  <0.001  Cardiorespiratory fitness (number of shuttles)  45.9 (25.9)  30.7 (14.9)  58.9 (26.2)  <0.001  Motor fitness (s)  11.7 (1.3)  12.4 (1.2)  11.1 (1.1)  <0.001  PF score  −0.0088 (2.9)  −0.52 (2.9)  0.44 (1.8)  <0.001  Mediterranean diet (KIDMED index)  7.1 (2.1)  7.3 (1.8)  7.0 (3.1)  0.086      Very low diet quality (≤3) (%)  6.4  4  8.4        Improvement is needed (4–7) (%)  52.8  53.2  52.4  0.020      Optimal Mediterranean diet (≥8) (%)  40.8  42.8  39.2    Socioeconomic status  6.4 (1.6)  6.4 (1.6)  6.3 (1.6)  0.011  Sleep duration average (h)  8.6 (0.9)  8.5 (0.9)  8.6 (0.9)  0.071  Sleep duration on weekends (h)  9.6 (1.6)  10.0 (1.4)  9.3 (1.6)  <0.001  HRQoL (Kidscreeen-10)  39.1 (5.6)  38.6 (5.7)  39.5 (5.4)  0.009  Pubertal stage-A, breast development in girls; genital development in boys. Pubertal stage-B, pubic hair development. a The data shown in percentage for categorical variables and mean for continuous variables. * P value was calculated based on Qui-squared test for categorical variables and t-test for continuous variables. Table 1 Descriptive characteristics of the participants by sex   Total (n = 956)a  Girls (n = 446)a  Boys (n = 510)a  P*  Age (year)  14.5 (1.8)  14.3 (1.7)  14.6 (1.9)  0.003  Body mass (kg)  55.9 (12.8)  53.6 (10.9)  57.9 (13.9)  <0.001  Height (cm)  1.61 (0.10)  1.58 (0.07)  1.64 (0.1)  <0.001  BMI (kg/m2)  21.1 (3.8)  21.1 (3.7)  21.1 (3.9)  0.882  Pubertal stage A (I/II–V) (%)  7.4/30.5/48.1/14  4/30.2/51.5/14.3  10.4/30.7/45.2/13.7  0.004  Pubertal stage B (I/II–V) (%)  5.9/21.3/52.2/20.5  2.7/23.3/51/23  8.7/19.7/53.3/18.3  0.001  Long jump (cm)  161 (33)  141.4 (24.1)  177.6 (30.3)  <0.001  Handgrip (kg)  27.8 (8.6)  23.3 (4.8)  31.7 (9.2)  <0.001  Handgrip/body mass (kg)  0.50 (0.1)  0.44 (0.09)  0.55 (0.12)  <0.001  Cardiorespiratory fitness (number of shuttles)  45.9 (25.9)  30.7 (14.9)  58.9 (26.2)  <0.001  Motor fitness (s)  11.7 (1.3)  12.4 (1.2)  11.1 (1.1)  <0.001  PF score  −0.0088 (2.9)  −0.52 (2.9)  0.44 (1.8)  <0.001  Mediterranean diet (KIDMED index)  7.1 (2.1)  7.3 (1.8)  7.0 (3.1)  0.086      Very low diet quality (≤3) (%)  6.4  4  8.4        Improvement is needed (4–7) (%)  52.8  53.2  52.4  0.020      Optimal Mediterranean diet (≥8) (%)  40.8  42.8  39.2    Socioeconomic status  6.4 (1.6)  6.4 (1.6)  6.3 (1.6)  0.011  Sleep duration average (h)  8.6 (0.9)  8.5 (0.9)  8.6 (0.9)  0.071  Sleep duration on weekends (h)  9.6 (1.6)  10.0 (1.4)  9.3 (1.6)  <0.001  HRQoL (Kidscreeen-10)  39.1 (5.6)  38.6 (5.7)  39.5 (5.4)  0.009    Total (n = 956)a  Girls (n = 446)a  Boys (n = 510)a  P*  Age (year)  14.5 (1.8)  14.3 (1.7)  14.6 (1.9)  0.003  Body mass (kg)  55.9 (12.8)  53.6 (10.9)  57.9 (13.9)  <0.001  Height (cm)  1.61 (0.10)  1.58 (0.07)  1.64 (0.1)  <0.001  BMI (kg/m2)  21.1 (3.8)  21.1 (3.7)  21.1 (3.9)  0.882  Pubertal stage A (I/II–V) (%)  7.4/30.5/48.1/14  4/30.2/51.5/14.3  10.4/30.7/45.2/13.7  0.004  Pubertal stage B (I/II–V) (%)  5.9/21.3/52.2/20.5  2.7/23.3/51/23  8.7/19.7/53.3/18.3  0.001  Long jump (cm)  161 (33)  141.4 (24.1)  177.6 (30.3)  <0.001  Handgrip (kg)  27.8 (8.6)  23.3 (4.8)  31.7 (9.2)  <0.001  Handgrip/body mass (kg)  0.50 (0.1)  0.44 (0.09)  0.55 (0.12)  <0.001  Cardiorespiratory fitness (number of shuttles)  45.9 (25.9)  30.7 (14.9)  58.9 (26.2)  <0.001  Motor fitness (s)  11.7 (1.3)  12.4 (1.2)  11.1 (1.1)  <0.001  PF score  −0.0088 (2.9)  −0.52 (2.9)  0.44 (1.8)  <0.001  Mediterranean diet (KIDMED index)  7.1 (2.1)  7.3 (1.8)  7.0 (3.1)  0.086      Very low diet quality (≤3) (%)  6.4  4  8.4        Improvement is needed (4–7) (%)  52.8  53.2  52.4  0.020      Optimal Mediterranean diet (≥8) (%)  40.8  42.8  39.2    Socioeconomic status  6.4 (1.6)  6.4 (1.6)  6.3 (1.6)  0.011  Sleep duration average (h)  8.6 (0.9)  8.5 (0.9)  8.6 (0.9)  0.071  Sleep duration on weekends (h)  9.6 (1.6)  10.0 (1.4)  9.3 (1.6)  <0.001  HRQoL (Kidscreeen-10)  39.1 (5.6)  38.6 (5.7)  39.5 (5.4)  0.009  Pubertal stage-A, breast development in girls; genital development in boys. Pubertal stage-B, pubic hair development. a The data shown in percentage for categorical variables and mean for continuous variables. * P value was calculated based on Qui-squared test for categorical variables and t-test for continuous variables. As shown in table 2, a significant association between PF score (B = 0.228; P < 0.05) and adherence to Mediterranean diet (B = 0.259; P < 0.05) and HRQoL was found, after adjustments for age, sex, pubertal stage, socioeconomic status, sleep duration and BMI (model 6). Table 2 Unstandardized regression coefficients examining the associations between PF and adherence to Mediterranean Diet and HRQoL   HRQoL   B (95% CI)  P-value  Model 1 (Crude)      Mediterranean diet  0.325 (0.159–0.490)  <0.001  Model 2 (Crude)      PF score  0.278 (0.161–0.394)  <0.001  Model 3 (Crude)      Mediterranean diet  0.314 (0.150–0.478)  <0.001      PF score  0.274 (0.158–0.390)  <0.001  Model 4 (adjusted for all confounders)      Mediterranean diet  0.275 (0.112–0.438)  0.001  Model 5 (adjusted for all confounders)      PF score  0.241 (0.107–0.374)  <0.001  Model 6 (adjusted for all confounders)      Mediterranean diet  0.259 (0.096–0.421)  0.002      PF score  0.228 (0.095–0.361)  0.001    HRQoL   B (95% CI)  P-value  Model 1 (Crude)      Mediterranean diet  0.325 (0.159–0.490)  <0.001  Model 2 (Crude)      PF score  0.278 (0.161–0.394)  <0.001  Model 3 (Crude)      Mediterranean diet  0.314 (0.150–0.478)  <0.001      PF score  0.274 (0.158–0.390)  <0.001  Model 4 (adjusted for all confounders)      Mediterranean diet  0.275 (0.112–0.438)  0.001  Model 5 (adjusted for all confounders)      PF score  0.241 (0.107–0.374)  <0.001  Model 6 (adjusted for all confounders)      Mediterranean diet  0.259 (0.096–0.421)  0.002      PF score  0.228 (0.095–0.361)  0.001  B, Unstandardized coefficients; CI, confidence interval. Models 1–3: unadjusted model. Models 4–6: adjusted for age, sex, pubertal stage (Tanners A and B), socioeconomic status, sleep duration and BMI. Table 2 Unstandardized regression coefficients examining the associations between PF and adherence to Mediterranean Diet and HRQoL   HRQoL   B (95% CI)  P-value  Model 1 (Crude)      Mediterranean diet  0.325 (0.159–0.490)  <0.001  Model 2 (Crude)      PF score  0.278 (0.161–0.394)  <0.001  Model 3 (Crude)      Mediterranean diet  0.314 (0.150–0.478)  <0.001      PF score  0.274 (0.158–0.390)  <0.001  Model 4 (adjusted for all confounders)      Mediterranean diet  0.275 (0.112–0.438)  0.001  Model 5 (adjusted for all confounders)      PF score  0.241 (0.107–0.374)  <0.001  Model 6 (adjusted for all confounders)      Mediterranean diet  0.259 (0.096–0.421)  0.002      PF score  0.228 (0.095–0.361)  0.001    HRQoL   B (95% CI)  P-value  Model 1 (Crude)      Mediterranean diet  0.325 (0.159–0.490)  <0.001  Model 2 (Crude)      PF score  0.278 (0.161–0.394)  <0.001  Model 3 (Crude)      Mediterranean diet  0.314 (0.150–0.478)  <0.001      PF score  0.274 (0.158–0.390)  <0.001  Model 4 (adjusted for all confounders)      Mediterranean diet  0.275 (0.112–0.438)  0.001  Model 5 (adjusted for all confounders)      PF score  0.241 (0.107–0.374)  <0.001  Model 6 (adjusted for all confounders)      Mediterranean diet  0.259 (0.096–0.421)  0.002      PF score  0.228 (0.095–0.361)  0.001  B, Unstandardized coefficients; CI, confidence interval. Models 1–3: unadjusted model. Models 4–6: adjusted for age, sex, pubertal stage (Tanners A and B), socioeconomic status, sleep duration and BMI. ANCOVA (figure 1) showed that adolescents with high PF and high adherence to Mediterranean diet had on average the highest HRQoL score (F(3, 939) = 4.270 P = 0.005). Significant differences were found for HRQoL score between low PF and low adherence to Mediterranean diet after adjustments for potential confounders. Figure 1 View largeDownload slide Mean value of HRQoL stratified in groups of PF (low or high) and adherence to Mediterranean diet (low or high). *Significantly different from the high PF/high adherence to Mediterranean diet (P < 0.05) Figure 1 View largeDownload slide Mean value of HRQoL stratified in groups of PF (low or high) and adherence to Mediterranean diet (low or high). *Significantly different from the high PF/high adherence to Mediterranean diet (P < 0.05) Discussion To the best of our knowledge this is one of the first studies to analyze the associations between all components of PF (cardiorespiratory, muscular and motor fitness) and adherence to Mediterranean diet with HRQoL among adolescents. Our data showed that adolescents with high overall PF and high adherence to Mediterranean diet had the highest HRQoL score. These results suggest that the combination of these two components of healthy lifestyle seem to be beneficial to adolescents’ HRQoL. In other words, the cross-sectional design of this study, PF and Mediterranean diet, seem to have a powerful combined and cumulative association on HRQoL in adolescents. This study also showed that adherence to the Mediterranean diet was significantly and positively associated with higher HRQoL scores, which is in line with a recent study with Spanish adolescents, suggesting that higher adherence to the Mediterranean diet predicted higher HRQoL scores.15 Likewise, another study with Greek adolescents revealed a significant positive association between adherence to the Mediterranean diet and HRQoL.16 Several biological and physiological mechanisms could explain the beneficial effect of the Mediterranean diet on physical health.25 Estruch et al.26 reported that greater adherence to the Mediterranean diet is associated with a significant improvement in general physical and psychological health, in longevity and lower levels of obesity, as well as lower incidence of atherosclerosis, metabolic syndrome and inflammation, and reduced risk of major chronic diseases. Some studies attribute the Mediterranean diet with some degree of protection with respect to cognitive impairment, dementia or depression incidence.27 Indeed, the Mediterranean diet is rich in nutrients such as antioxidants, fibre, minerals, vitamins, omega-3 fatty acids (from fish) and monounsaturated fatty acids (from olive oil), whose beneficial effects on health have been recurrently established28 Recently, some studies suggested the protective role of olive oil in mental disorders29 and physical benefits.30 The consumption of fish has also been related to better HRQoL because of its content in beneficial nutrients for health such as omega-3 fatty acids, vitamins and antioxidants.25 Moreover, the consumption of fruits and vegetables has a positive association with physical and mental health status.31 We found a significant association between PF score and HRQoL, after adjustments for all confounders, which is consistent with other studies.5,6 For example, Gu et al.6 examined the association between PF and HRQoL and found that all components of PF were significantly related to physical and mental functioning of HRQoL, except flexibility. Another study, with Portuguese adolescents from the HBSC study, showed that self-reported fitness levels (overall fitness) were positively and significantly associated with HRQoL.5 PF is considered one of the most important health status markers that predicts cardiovascular disease and mortality.32 Evidence suggests that the development of all components of PF early in life is of serious importance to maintaining PF and health outcomes later on in life.33 However, a major determinant of PF is the level of physical activity.34 The pathways by which physical activity and fitness are associated with physical and psychological well-being are still not fully perceived in adolescents; however, some mechanisms have been postulated for children.35 For example, regular physical activity increases fitness and thus improves vascular and metabolic function36 and leads to favourable structural and functional neuronal adaptations,37 and improves attention, emotions, inhibitory control and academic performance.38 Our results suggest that maintaining and enhancing PF in adolescents has the potential of yielding physical and mental health benefits. Our data also pointed-out that girls had significantly lower HRQoL scores than boys, which is in line with previous findings.39,40 These, sex differences in HRQoL could be explained by advanced pubertal development and social factors that may predict lower psychological well-being and negative body image in girls. Some limitations of this study should be recognized. First, this is a cross-sectional study that does not allow us to establish causality. Second, we used a sum score from the Kidscreen-10 questionnaire, which does not allow analyses for each of the dimensions of HRQoL and is verified in extended versions of this scale (27- and 53-items). Third, we cannot rule out some reporting bias because we used self-reported dietary intake data. Important strengths of this study include the evaluation of both independent and combined associations of lifestyle variables (PF and Mediterranean diet) that have been shown to be associated with HRQoL; the study was conducted on a relative large sample of adolescents. We controlled for a wide range of covariates, including socioeconomic status and sleep duration that are related with HRQoL. In conclusion, we have shown that the combination of high PF levels and optimal adherence to Mediterranean diet is positively associated with better HRQoL scores in Portuguese adolescents. The self-perceived health of adolescents is increasingly recognized as a relevant outcome in public health research. As a result, more studies investigating the effect of Mediterranean diet and PF on HRQoL in youth are needed. Acknowledgements The authors gratefully acknowledge the participation of all adolescents and their parents, teachers and schools of the LabMed Physical Activity Study. They also acknowledge the cooperation of volunteer’s subjects and the Research Centre in Physical Activity, Health and Leisure (University of Porto) for the sponsoring the LabMed Physical Activity Study. Funding This study was supported by the Portuguese Foundation for Science and Technology (FCT) grants: SFRH/BD/88984/2012 and UID/DTP/00617/2013; Research Centre in Physical Activity, Health and Leisure (CIAFEL), Faculty of Sport—University of Porto—Portugal. R.S. has a Discovery Early Career Research Award from the Australian Research Council (DE150101921). C.A.-S. is supported by a Doctoral Scholarship from Brazilian government by CAPES (Coordination of Improvement of Higher Education Personnel) (Proc: 9588-13-2). Conflicts of interest: None declared. Key points Aside from the effects on biological parameters, the consideration of associations between physical fitness with psychosocial aspects of health should be taken into account. Both physical fitness and adherence to a healthy dietary pattern should be considered in intervention programmes to improve psychosocial aspects of health and well-being. Measuring health-related quality of life is important as a way of monitoring the health of the population. References 1 Ravens-Sieberer U, Erhart M, Wille D-PN, et al.   Health-related quality of life in children and adolescents in Germany: results of the BELLA study. Eur Child Adolesc Psychiatry  2008; 17: 148– 56. Google Scholar CrossRef Search ADS PubMed  2 Patton G, Viner R. Pubertal transitions in health. Lancet  2007; 369: 1130– 9. Google Scholar CrossRef Search ADS PubMed  3 Ruiz J, Castro-Piñero J, España-Romero V, et al.   Field-based fitness assessment in young people: the ALPHA health-related fitness test battery for children and adolescents. Br J Sports Med  2011; 45: 518– 24. 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Google Scholar CrossRef Search ADS   16 Costarelli V, Koretsi E, Georgitsogianni E. Health-related quality of life of Greek adolescents: the role of the Mediterranean diet. Qual Life Res  2013; 22: 951– 6. Google Scholar CrossRef Search ADS PubMed  17 Agostinis-Sobrinho C, Santos R, Moreira C, et al.   Association between serum adiponectin levels and muscular fitness in Portuguese adolescents: LabMed Physical Activity Study. Nutr Metab Cardiovasc Dis  2016; 26: 517– 24. Google Scholar CrossRef Search ADS PubMed  18 Matos M, Gaspar T, Simões C. Health-related quality of life in Portuguese children and adolescents. Psicol Reflex Crit  2012; 25: 230– 7. Google Scholar CrossRef Search ADS   19 Ruiz J, España-Romero V, Ortega F, et al.   Hand span influences optimal grip span in male and female teenagers. J Hand Surg  2006; 31: 1367– 72. 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Google Scholar CrossRef Search ADS PubMed  24 Currie C, Molcho M, Boyce W, et al.   Researching health inequalities in adolescents: the development of the Health Behaviour in School-Aged Children (HBSC) family affluence scale. Soc Sci Med  2008; 66: 1429– 36. Google Scholar CrossRef Search ADS PubMed  25 Sánchez P, Ruano C, De Irala J, et al.   Adherence to the Mediterranean diet and quality of life in the SUN Project. Eur J Clin Nutr  2012; 66: 360– 8. Google Scholar CrossRef Search ADS PubMed  26 Estruch R, Ros E, Salas-Salvadó J, et al.   Primary prevention of cardiovascular disease with a Mediterranean diet. N Engl J Med  2013; 368: 1279– 90. Google Scholar CrossRef Search ADS PubMed  27 Sánchez-Villegas A, Delgado-Rodríguez M, Alonso A, et al.   Association of the Mediterranean dietary pattern with the incidence of depression: the Seguimiento Universidad de Navarra/University of Navarra follow-up (SUN) cohort. Arch Gen Psychiatry  2009; 66: 1090– 8. 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Google Scholar CrossRef Search ADS PubMed  32 Ortega FB, Ruiz JR, Castillo MJ, Sjöström M. Physical fitness in childhood and adolescence: a powerful marker of health. Int J Obes  2008; 32: 1– 11. Google Scholar CrossRef Search ADS   33 Ried-Larsen M, Grøntved A, Kristensen P, et al.   Moderate-and-vigorous physical activity from adolescence to adulthood and subclinical atherosclerosis in adulthood: prospective observations from the European Youth Heart Study. Br J Sports Med  2015; 49: 107– 12. Google Scholar CrossRef Search ADS PubMed  34 Bürgi F, Meyer U, Granacher U, et al.   Relationship of physical activity with motor skills, aerobic fitness and body fat in preschool children: a cross-sectional and longitudinal study (Ballabeina). Int J Obes  2011; 35: 937. Google Scholar CrossRef Search ADS   35 Gerber M, Endes K, Brand S, et al.   In 6-to 8-year-old children, cardiorespiratory fitness moderates the relationship between severity of life events and health-related quality of life. 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Google Scholar CrossRef Search ADS PubMed  40 Bolton K, Kremer P, Rossthorn N, et al.   The effect of gender and age on the association between weight status and health-related quality of life in Australian adolescents. BMC Public Health  2014; 14: 1– 8. Google Scholar CrossRef Search ADS PubMed  © The Author(s) 2018. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The European Journal of Public Health Oxford University Press

Associations between physical fitness and adherence to the Mediterranean diet with health-related quality of life in adolescents: results from the LabMed Physical Activity Study

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved.
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1101-1262
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1464-360X
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10.1093/eurpub/cky043
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Abstract

Abstract Background Physical fitness (PF) and adherence to the Mediterranean diet are important indicators of healthy lifestyles. The purpose of this study is to analyze the independent and combined associations between PF and adherence to Mediterranean diet with health-related quality of life (HRQoL) in adolescents. Methods This is a cross-sectional analysis with 956 Portuguese adolescents aged 12–18 years. HRQoL was measured with the Kidscreen-10 questionnaire. PF was assessed with the ALPHA health-related fitness battery. The 20-m shuttle run test was used for the estimation of cardiorespiratory fitness; handgrip strength and standing long jump tests were applied for the assessment of muscular fitness and the 4 × 10 m shuttle run test for the assessment of motor fitness (speed and agility). The results of the PF tests (cardiorespiratory fitness, muscular fitness and motor fitness) were transformed into standardized values (Z-scores) by age and sex. Adherence to the Mediterranean diet was assessed with the KIDMED index. Regression analysis and analysis of covariance were performed. Results PF (B = 0.228; P < 0.05) and adherence to the Mediterranean diet (B = 0.259; P < 0.05) were positively associated with HRQoL, after controlling for several variables. Participants classified as high PF and high adherence to Mediterranean diet had on average the highest HRQoL score compared with those with low PF and low adherence to Mediterranean diet (F(3, 939) = 4.270; P = 0.005), after adjustments for potential confounders. Conclusions The combination of high PF levels and optimal adherence to Mediterranean diet is positively associated with HRQoL. Introduction Health-related quality of life (HRQoL) is a multidimensional construct that relates to a person’s self-perceived health and consists of ratings of well-being and functionality, including physical well-being/functioning, emotional well-being, self-esteem, social functioning and family relations.1 During adolescence, several biological, physical, cognitive, psychological, social and emotional factors can affect one’s HRQoL and well-being.2 Physical fitness (PF) has been associated with health benefits in young people3 and is considered a marker of a healthy lifestyle, as well as a predictor of morbidity and mortality from cardiovascular disease and other causes.4 Previous data from Portuguese adolescents from the Health Behaviour in School-Aged Children (HBSC) study showed that self-reported fitness levels were positively associated with HRQoL.5 Likewise, three other studies indicated that both cardiorespiratory fitness and muscular fitness were positively associated with HRQoL in schoolchildren aged 8–11 years.6–8 The Mediterranean diet is considered one of the healthiest dietary patterns.9 Indeed, several studies have shown that greater adherence to a Mediterranean-like dietary pattern is associated with an improved health status10 with beneficial effects on arterial stiffness11; academic performance12 and the intensity of physical activity behaviour.13 However, recent data indicates that adherence to this dietary pattern is decreasing in Mediterranean regions, particularly among children and adolescents.14 Some recent studies have investigated the associations between Mediterranean diet and HRQoL in adolescents15,16 and reported positive associations between HRQoL and adherence to Mediterranean diet in youth. However, few studies have addressed the relationship between overall PF and Mediterranean diet with HRQoL in adolescents. Therefore, the aim of this study was to examine the independent combined associations between PF and adherence to the Mediterranean diet with HRQoL in adolescents. Methods Study design and sample The current report is part of the ‘Longitudinal Analysis of Biomarkers and Environmental Determinants of Physical Activity (LabMed Physical Activity Study)’, a school-based prospective cohort study carried out in five Portuguese cities from the Northern Region. The full description of the study protocol and measures can be seen in detail elsewhere.17 Briefly, baseline data was collected in the fall of 2011, for all students that agreed to participate in the study (n = 1229; aged 12–18 years). From this initial total sample, 956 adolescents (446 girls and 510 boys) had provided complete data on the variables of interest of the present report and therefore were included in this study. The study was conducted in accordance with the Portuguese Data Protection Authority (#1112434/2011), and the Portuguese Ministry of Science and Education (0246200001/2011) and the Faculty of Sports of University of Porto approved the study. All participants were informed of the study’s goals, and written informed consent was obtained from participating adolescents as well as from their parents or tutors. Measurements Health-related quality of life HRQoL was assessed by Kidscreen-10 questionnaire. It contains 10 items regarding family life, peers and school life. Kidscreen-10 is a one-dimensional measure that represents a global score adequate for use in large epidemiological surveys.18 Physical fitness PF was assessed following the protocols of the ALPHA health-related fitness battery.3 Participants performed the following tests: 20-m shuttle run test to estimate cardiorespiratory fitness; handgrip strength and standing long jump tests for the assessment of muscular fitness and, the 4 × 10 m shuttle run test to assess motor fitness (speed and agility). For the 20-m shuttle run test the participants were required to run in a straight line, between two lines distanced 20-m apart, while keeping pace with a pre-recorded audio CD. The initial speed was 8.5 km.h−1, which was increased by 0.5 km.h−1 each minute (1 min = one stage). The test was finished when the adolescent failed to reach the end lines before the audio signal on two occasions. The number of shuttles was recorded. Upper body isometric strength was assessed using a handgrip dynamometer, (T.K.K. 5001, Grip-A produced by Takei, Japan), adjusted by sex and hand size of each adolescent using the equations specifically developed for adolescents.19 Participants were instructed to stand with their arms by their side, fully extended, squeezing the handgrip continuously for at least 2 s, performing the test with the right and left hands in turn. A rest period of 90-s was given between trials. The test was performed twice and the best score recorded for each hand was used for analysis. The handgrip score (in kg) was calculated as the average of the left and right best scores and then was expressed in kilograms of body mass.20 In the standing long jump test (lower body explosive strength), the adolescents were instructed to jump, from the starting line and to push off vigorously and jump as far forward as possible landing on both feet and staying upright. The test was performed twice and the best distance was recorded in centimeters for analysis. The distance between the first heel-mark and the take-off line determined the standing jump score.3 For motor fitness, the participants were asked to run 4 × 10 m (back and forth), as fast as possible. Two parallel lines were drawn on the floor 10-m apart. In the start line, there was one sponge (B) and in the opposite line there were two sponges (A, C). When the start was given, the participant (without sponge) ran as fast as possible to the other line and returned to the starting line with the sponge (A), crossing both lines with both feet, then sponge (A) was changed by the sponge B in the starting line. Afterwards, the participant went back running as fast as possible to the opposite line and changed the sponge B by the C, and then ran back to the starting line. The test was performed twice and the best score was recorded in seconds for analysis. Lower scores indicate better performance. The results of the PF tests (cardiorespiratory fitness, muscular fitness and motor fitness) were transformed into standardized values (Z-scores) by age and sex. The Z-score of motor fitness was multiplied by −1, because a lower score indicates better performance. Then, the sum of the Z-Scores of tests was used to create the PF score. High PF score was considered when the participant had ≥1 SD of this Z-score. Adherence to Mediterranean diet Participants self-reported their dietary intake with the KIDMED index (Mediterranean Diet Quality Index for children and adolescents) developed by Serra-Majem et al.21 The final scores of the KIDMED index vary between 0 and 12 points, with higher scores indicating higher adherence to the Mediterranean diet. Participants were classified into three categories: (i) ≥8, optimal Mediterranean diet; (ii) 4–7, improvement is needed to adjust intake to Mediterranean patterns and (iii) ≤3, very low diet quality as proposed by Kontogianni.22 Body mass and height Anthropometric measurements were performed according to standard procedures. Body mass and height were measured using a portable electronic weight scale (Tanita Inner Scan BC 532, Tokyo, Japan) and a portable stadiometer (Seca 213, Hamburg, Germany), respectively, with the participant barefoot, wearing light clothing. Body mass index (BMI) was calculated as body mass divided by stature squared (kg/m2). Pubertal stage Adolescents self-reported their pubertal stage (from 1 to 5) relatively the secondary sex characteristics, according to the criteria of Tanner and Whitehouse.23 Girls were assessed by the stage of breast development (Tanner A) and public hair distribution (Tanner B), and boys by the stage of genitalia development (penis size and testicular volume—Tanner A) and pubic hair distribution (Tanner B). Socioeconomic status Adolescents’ socioeconomic status was assessed using the Family Affluence Scale,24 a four-item questionnaire where the participants report whether their family owns a car, whether they have his/her own bedroom, the number of family vacations during the last 12 months and the number of computers that the family owns. The items are summed to give a final socioeconomic index ranging from 0 to 9 points, with higher scores indicating higher socioeconomic status. Sleep duration Habitual sleep duration was self-reported, using the HBSC questionnaire. Adolescents were asked what time they usually woke up in the morning and what time they usually went to bed at night on a typical school day and on a typical weekend day. Average sleep duration per night was calculated as follows: 5 × sleep duration on weekdays plus 2 × sleep duration on weekend days. Statistical analysis Descriptive data are presented as means and standard deviations for continuous variables and in the case of the categorical variables as frequencies and percentages. To assess differences between sexes, the independent student’s t-test was used for the continuous variables and chi-square test for the categorical variables. Linear regression models were performed to determine the associations between PF and Mediterranean diet score (as predictors—independent and combined) and HRQoL (as dependent variable), adjusted for age, sex, pubertal stage, socioeconomic status, sleep duration and BMI. Unstandardized regression coefficients were used to express the B coefficients of the regression analyses. Analysis of covariance (ANCOVA) with Bonferroni post hoc multiple comparison tests were used to assess the differences between mean values of HRQoL across groups of PF (low and high) and adherence to Mediterranean diet: low (the first two categories collapsed ‘improvement is needed’ and ‘very low quality diet’) and high (‘optimal Mediterranean diet’). Covariates included were age, sex, pubertal stage, socioeconomic status, sleep duration and BMI. Data analyses were performed with the statistical software Statistical Package for Social Sciences (Windows version 24.0; SPSS Inc., Chicago, IL, USA). A P values < 0.05 was considered to indicate statistical significance. Results Table 1 shows the descriptive characteristics of the participants. Boys outperformed girls in all PF tests (P < 0.001 for all), while girls reported a significantly higher optimal adherence to the Mediterranean diet (P = 0.020) than boys. Table 1 Descriptive characteristics of the participants by sex   Total (n = 956)a  Girls (n = 446)a  Boys (n = 510)a  P*  Age (year)  14.5 (1.8)  14.3 (1.7)  14.6 (1.9)  0.003  Body mass (kg)  55.9 (12.8)  53.6 (10.9)  57.9 (13.9)  <0.001  Height (cm)  1.61 (0.10)  1.58 (0.07)  1.64 (0.1)  <0.001  BMI (kg/m2)  21.1 (3.8)  21.1 (3.7)  21.1 (3.9)  0.882  Pubertal stage A (I/II–V) (%)  7.4/30.5/48.1/14  4/30.2/51.5/14.3  10.4/30.7/45.2/13.7  0.004  Pubertal stage B (I/II–V) (%)  5.9/21.3/52.2/20.5  2.7/23.3/51/23  8.7/19.7/53.3/18.3  0.001  Long jump (cm)  161 (33)  141.4 (24.1)  177.6 (30.3)  <0.001  Handgrip (kg)  27.8 (8.6)  23.3 (4.8)  31.7 (9.2)  <0.001  Handgrip/body mass (kg)  0.50 (0.1)  0.44 (0.09)  0.55 (0.12)  <0.001  Cardiorespiratory fitness (number of shuttles)  45.9 (25.9)  30.7 (14.9)  58.9 (26.2)  <0.001  Motor fitness (s)  11.7 (1.3)  12.4 (1.2)  11.1 (1.1)  <0.001  PF score  −0.0088 (2.9)  −0.52 (2.9)  0.44 (1.8)  <0.001  Mediterranean diet (KIDMED index)  7.1 (2.1)  7.3 (1.8)  7.0 (3.1)  0.086      Very low diet quality (≤3) (%)  6.4  4  8.4        Improvement is needed (4–7) (%)  52.8  53.2  52.4  0.020      Optimal Mediterranean diet (≥8) (%)  40.8  42.8  39.2    Socioeconomic status  6.4 (1.6)  6.4 (1.6)  6.3 (1.6)  0.011  Sleep duration average (h)  8.6 (0.9)  8.5 (0.9)  8.6 (0.9)  0.071  Sleep duration on weekends (h)  9.6 (1.6)  10.0 (1.4)  9.3 (1.6)  <0.001  HRQoL (Kidscreeen-10)  39.1 (5.6)  38.6 (5.7)  39.5 (5.4)  0.009    Total (n = 956)a  Girls (n = 446)a  Boys (n = 510)a  P*  Age (year)  14.5 (1.8)  14.3 (1.7)  14.6 (1.9)  0.003  Body mass (kg)  55.9 (12.8)  53.6 (10.9)  57.9 (13.9)  <0.001  Height (cm)  1.61 (0.10)  1.58 (0.07)  1.64 (0.1)  <0.001  BMI (kg/m2)  21.1 (3.8)  21.1 (3.7)  21.1 (3.9)  0.882  Pubertal stage A (I/II–V) (%)  7.4/30.5/48.1/14  4/30.2/51.5/14.3  10.4/30.7/45.2/13.7  0.004  Pubertal stage B (I/II–V) (%)  5.9/21.3/52.2/20.5  2.7/23.3/51/23  8.7/19.7/53.3/18.3  0.001  Long jump (cm)  161 (33)  141.4 (24.1)  177.6 (30.3)  <0.001  Handgrip (kg)  27.8 (8.6)  23.3 (4.8)  31.7 (9.2)  <0.001  Handgrip/body mass (kg)  0.50 (0.1)  0.44 (0.09)  0.55 (0.12)  <0.001  Cardiorespiratory fitness (number of shuttles)  45.9 (25.9)  30.7 (14.9)  58.9 (26.2)  <0.001  Motor fitness (s)  11.7 (1.3)  12.4 (1.2)  11.1 (1.1)  <0.001  PF score  −0.0088 (2.9)  −0.52 (2.9)  0.44 (1.8)  <0.001  Mediterranean diet (KIDMED index)  7.1 (2.1)  7.3 (1.8)  7.0 (3.1)  0.086      Very low diet quality (≤3) (%)  6.4  4  8.4        Improvement is needed (4–7) (%)  52.8  53.2  52.4  0.020      Optimal Mediterranean diet (≥8) (%)  40.8  42.8  39.2    Socioeconomic status  6.4 (1.6)  6.4 (1.6)  6.3 (1.6)  0.011  Sleep duration average (h)  8.6 (0.9)  8.5 (0.9)  8.6 (0.9)  0.071  Sleep duration on weekends (h)  9.6 (1.6)  10.0 (1.4)  9.3 (1.6)  <0.001  HRQoL (Kidscreeen-10)  39.1 (5.6)  38.6 (5.7)  39.5 (5.4)  0.009  Pubertal stage-A, breast development in girls; genital development in boys. Pubertal stage-B, pubic hair development. a The data shown in percentage for categorical variables and mean for continuous variables. * P value was calculated based on Qui-squared test for categorical variables and t-test for continuous variables. Table 1 Descriptive characteristics of the participants by sex   Total (n = 956)a  Girls (n = 446)a  Boys (n = 510)a  P*  Age (year)  14.5 (1.8)  14.3 (1.7)  14.6 (1.9)  0.003  Body mass (kg)  55.9 (12.8)  53.6 (10.9)  57.9 (13.9)  <0.001  Height (cm)  1.61 (0.10)  1.58 (0.07)  1.64 (0.1)  <0.001  BMI (kg/m2)  21.1 (3.8)  21.1 (3.7)  21.1 (3.9)  0.882  Pubertal stage A (I/II–V) (%)  7.4/30.5/48.1/14  4/30.2/51.5/14.3  10.4/30.7/45.2/13.7  0.004  Pubertal stage B (I/II–V) (%)  5.9/21.3/52.2/20.5  2.7/23.3/51/23  8.7/19.7/53.3/18.3  0.001  Long jump (cm)  161 (33)  141.4 (24.1)  177.6 (30.3)  <0.001  Handgrip (kg)  27.8 (8.6)  23.3 (4.8)  31.7 (9.2)  <0.001  Handgrip/body mass (kg)  0.50 (0.1)  0.44 (0.09)  0.55 (0.12)  <0.001  Cardiorespiratory fitness (number of shuttles)  45.9 (25.9)  30.7 (14.9)  58.9 (26.2)  <0.001  Motor fitness (s)  11.7 (1.3)  12.4 (1.2)  11.1 (1.1)  <0.001  PF score  −0.0088 (2.9)  −0.52 (2.9)  0.44 (1.8)  <0.001  Mediterranean diet (KIDMED index)  7.1 (2.1)  7.3 (1.8)  7.0 (3.1)  0.086      Very low diet quality (≤3) (%)  6.4  4  8.4        Improvement is needed (4–7) (%)  52.8  53.2  52.4  0.020      Optimal Mediterranean diet (≥8) (%)  40.8  42.8  39.2    Socioeconomic status  6.4 (1.6)  6.4 (1.6)  6.3 (1.6)  0.011  Sleep duration average (h)  8.6 (0.9)  8.5 (0.9)  8.6 (0.9)  0.071  Sleep duration on weekends (h)  9.6 (1.6)  10.0 (1.4)  9.3 (1.6)  <0.001  HRQoL (Kidscreeen-10)  39.1 (5.6)  38.6 (5.7)  39.5 (5.4)  0.009    Total (n = 956)a  Girls (n = 446)a  Boys (n = 510)a  P*  Age (year)  14.5 (1.8)  14.3 (1.7)  14.6 (1.9)  0.003  Body mass (kg)  55.9 (12.8)  53.6 (10.9)  57.9 (13.9)  <0.001  Height (cm)  1.61 (0.10)  1.58 (0.07)  1.64 (0.1)  <0.001  BMI (kg/m2)  21.1 (3.8)  21.1 (3.7)  21.1 (3.9)  0.882  Pubertal stage A (I/II–V) (%)  7.4/30.5/48.1/14  4/30.2/51.5/14.3  10.4/30.7/45.2/13.7  0.004  Pubertal stage B (I/II–V) (%)  5.9/21.3/52.2/20.5  2.7/23.3/51/23  8.7/19.7/53.3/18.3  0.001  Long jump (cm)  161 (33)  141.4 (24.1)  177.6 (30.3)  <0.001  Handgrip (kg)  27.8 (8.6)  23.3 (4.8)  31.7 (9.2)  <0.001  Handgrip/body mass (kg)  0.50 (0.1)  0.44 (0.09)  0.55 (0.12)  <0.001  Cardiorespiratory fitness (number of shuttles)  45.9 (25.9)  30.7 (14.9)  58.9 (26.2)  <0.001  Motor fitness (s)  11.7 (1.3)  12.4 (1.2)  11.1 (1.1)  <0.001  PF score  −0.0088 (2.9)  −0.52 (2.9)  0.44 (1.8)  <0.001  Mediterranean diet (KIDMED index)  7.1 (2.1)  7.3 (1.8)  7.0 (3.1)  0.086      Very low diet quality (≤3) (%)  6.4  4  8.4        Improvement is needed (4–7) (%)  52.8  53.2  52.4  0.020      Optimal Mediterranean diet (≥8) (%)  40.8  42.8  39.2    Socioeconomic status  6.4 (1.6)  6.4 (1.6)  6.3 (1.6)  0.011  Sleep duration average (h)  8.6 (0.9)  8.5 (0.9)  8.6 (0.9)  0.071  Sleep duration on weekends (h)  9.6 (1.6)  10.0 (1.4)  9.3 (1.6)  <0.001  HRQoL (Kidscreeen-10)  39.1 (5.6)  38.6 (5.7)  39.5 (5.4)  0.009  Pubertal stage-A, breast development in girls; genital development in boys. Pubertal stage-B, pubic hair development. a The data shown in percentage for categorical variables and mean for continuous variables. * P value was calculated based on Qui-squared test for categorical variables and t-test for continuous variables. As shown in table 2, a significant association between PF score (B = 0.228; P < 0.05) and adherence to Mediterranean diet (B = 0.259; P < 0.05) and HRQoL was found, after adjustments for age, sex, pubertal stage, socioeconomic status, sleep duration and BMI (model 6). Table 2 Unstandardized regression coefficients examining the associations between PF and adherence to Mediterranean Diet and HRQoL   HRQoL   B (95% CI)  P-value  Model 1 (Crude)      Mediterranean diet  0.325 (0.159–0.490)  <0.001  Model 2 (Crude)      PF score  0.278 (0.161–0.394)  <0.001  Model 3 (Crude)      Mediterranean diet  0.314 (0.150–0.478)  <0.001      PF score  0.274 (0.158–0.390)  <0.001  Model 4 (adjusted for all confounders)      Mediterranean diet  0.275 (0.112–0.438)  0.001  Model 5 (adjusted for all confounders)      PF score  0.241 (0.107–0.374)  <0.001  Model 6 (adjusted for all confounders)      Mediterranean diet  0.259 (0.096–0.421)  0.002      PF score  0.228 (0.095–0.361)  0.001    HRQoL   B (95% CI)  P-value  Model 1 (Crude)      Mediterranean diet  0.325 (0.159–0.490)  <0.001  Model 2 (Crude)      PF score  0.278 (0.161–0.394)  <0.001  Model 3 (Crude)      Mediterranean diet  0.314 (0.150–0.478)  <0.001      PF score  0.274 (0.158–0.390)  <0.001  Model 4 (adjusted for all confounders)      Mediterranean diet  0.275 (0.112–0.438)  0.001  Model 5 (adjusted for all confounders)      PF score  0.241 (0.107–0.374)  <0.001  Model 6 (adjusted for all confounders)      Mediterranean diet  0.259 (0.096–0.421)  0.002      PF score  0.228 (0.095–0.361)  0.001  B, Unstandardized coefficients; CI, confidence interval. Models 1–3: unadjusted model. Models 4–6: adjusted for age, sex, pubertal stage (Tanners A and B), socioeconomic status, sleep duration and BMI. Table 2 Unstandardized regression coefficients examining the associations between PF and adherence to Mediterranean Diet and HRQoL   HRQoL   B (95% CI)  P-value  Model 1 (Crude)      Mediterranean diet  0.325 (0.159–0.490)  <0.001  Model 2 (Crude)      PF score  0.278 (0.161–0.394)  <0.001  Model 3 (Crude)      Mediterranean diet  0.314 (0.150–0.478)  <0.001      PF score  0.274 (0.158–0.390)  <0.001  Model 4 (adjusted for all confounders)      Mediterranean diet  0.275 (0.112–0.438)  0.001  Model 5 (adjusted for all confounders)      PF score  0.241 (0.107–0.374)  <0.001  Model 6 (adjusted for all confounders)      Mediterranean diet  0.259 (0.096–0.421)  0.002      PF score  0.228 (0.095–0.361)  0.001    HRQoL   B (95% CI)  P-value  Model 1 (Crude)      Mediterranean diet  0.325 (0.159–0.490)  <0.001  Model 2 (Crude)      PF score  0.278 (0.161–0.394)  <0.001  Model 3 (Crude)      Mediterranean diet  0.314 (0.150–0.478)  <0.001      PF score  0.274 (0.158–0.390)  <0.001  Model 4 (adjusted for all confounders)      Mediterranean diet  0.275 (0.112–0.438)  0.001  Model 5 (adjusted for all confounders)      PF score  0.241 (0.107–0.374)  <0.001  Model 6 (adjusted for all confounders)      Mediterranean diet  0.259 (0.096–0.421)  0.002      PF score  0.228 (0.095–0.361)  0.001  B, Unstandardized coefficients; CI, confidence interval. Models 1–3: unadjusted model. Models 4–6: adjusted for age, sex, pubertal stage (Tanners A and B), socioeconomic status, sleep duration and BMI. ANCOVA (figure 1) showed that adolescents with high PF and high adherence to Mediterranean diet had on average the highest HRQoL score (F(3, 939) = 4.270 P = 0.005). Significant differences were found for HRQoL score between low PF and low adherence to Mediterranean diet after adjustments for potential confounders. Figure 1 View largeDownload slide Mean value of HRQoL stratified in groups of PF (low or high) and adherence to Mediterranean diet (low or high). *Significantly different from the high PF/high adherence to Mediterranean diet (P < 0.05) Figure 1 View largeDownload slide Mean value of HRQoL stratified in groups of PF (low or high) and adherence to Mediterranean diet (low or high). *Significantly different from the high PF/high adherence to Mediterranean diet (P < 0.05) Discussion To the best of our knowledge this is one of the first studies to analyze the associations between all components of PF (cardiorespiratory, muscular and motor fitness) and adherence to Mediterranean diet with HRQoL among adolescents. Our data showed that adolescents with high overall PF and high adherence to Mediterranean diet had the highest HRQoL score. These results suggest that the combination of these two components of healthy lifestyle seem to be beneficial to adolescents’ HRQoL. In other words, the cross-sectional design of this study, PF and Mediterranean diet, seem to have a powerful combined and cumulative association on HRQoL in adolescents. This study also showed that adherence to the Mediterranean diet was significantly and positively associated with higher HRQoL scores, which is in line with a recent study with Spanish adolescents, suggesting that higher adherence to the Mediterranean diet predicted higher HRQoL scores.15 Likewise, another study with Greek adolescents revealed a significant positive association between adherence to the Mediterranean diet and HRQoL.16 Several biological and physiological mechanisms could explain the beneficial effect of the Mediterranean diet on physical health.25 Estruch et al.26 reported that greater adherence to the Mediterranean diet is associated with a significant improvement in general physical and psychological health, in longevity and lower levels of obesity, as well as lower incidence of atherosclerosis, metabolic syndrome and inflammation, and reduced risk of major chronic diseases. Some studies attribute the Mediterranean diet with some degree of protection with respect to cognitive impairment, dementia or depression incidence.27 Indeed, the Mediterranean diet is rich in nutrients such as antioxidants, fibre, minerals, vitamins, omega-3 fatty acids (from fish) and monounsaturated fatty acids (from olive oil), whose beneficial effects on health have been recurrently established28 Recently, some studies suggested the protective role of olive oil in mental disorders29 and physical benefits.30 The consumption of fish has also been related to better HRQoL because of its content in beneficial nutrients for health such as omega-3 fatty acids, vitamins and antioxidants.25 Moreover, the consumption of fruits and vegetables has a positive association with physical and mental health status.31 We found a significant association between PF score and HRQoL, after adjustments for all confounders, which is consistent with other studies.5,6 For example, Gu et al.6 examined the association between PF and HRQoL and found that all components of PF were significantly related to physical and mental functioning of HRQoL, except flexibility. Another study, with Portuguese adolescents from the HBSC study, showed that self-reported fitness levels (overall fitness) were positively and significantly associated with HRQoL.5 PF is considered one of the most important health status markers that predicts cardiovascular disease and mortality.32 Evidence suggests that the development of all components of PF early in life is of serious importance to maintaining PF and health outcomes later on in life.33 However, a major determinant of PF is the level of physical activity.34 The pathways by which physical activity and fitness are associated with physical and psychological well-being are still not fully perceived in adolescents; however, some mechanisms have been postulated for children.35 For example, regular physical activity increases fitness and thus improves vascular and metabolic function36 and leads to favourable structural and functional neuronal adaptations,37 and improves attention, emotions, inhibitory control and academic performance.38 Our results suggest that maintaining and enhancing PF in adolescents has the potential of yielding physical and mental health benefits. Our data also pointed-out that girls had significantly lower HRQoL scores than boys, which is in line with previous findings.39,40 These, sex differences in HRQoL could be explained by advanced pubertal development and social factors that may predict lower psychological well-being and negative body image in girls. Some limitations of this study should be recognized. First, this is a cross-sectional study that does not allow us to establish causality. Second, we used a sum score from the Kidscreen-10 questionnaire, which does not allow analyses for each of the dimensions of HRQoL and is verified in extended versions of this scale (27- and 53-items). Third, we cannot rule out some reporting bias because we used self-reported dietary intake data. Important strengths of this study include the evaluation of both independent and combined associations of lifestyle variables (PF and Mediterranean diet) that have been shown to be associated with HRQoL; the study was conducted on a relative large sample of adolescents. We controlled for a wide range of covariates, including socioeconomic status and sleep duration that are related with HRQoL. In conclusion, we have shown that the combination of high PF levels and optimal adherence to Mediterranean diet is positively associated with better HRQoL scores in Portuguese adolescents. The self-perceived health of adolescents is increasingly recognized as a relevant outcome in public health research. As a result, more studies investigating the effect of Mediterranean diet and PF on HRQoL in youth are needed. Acknowledgements The authors gratefully acknowledge the participation of all adolescents and their parents, teachers and schools of the LabMed Physical Activity Study. They also acknowledge the cooperation of volunteer’s subjects and the Research Centre in Physical Activity, Health and Leisure (University of Porto) for the sponsoring the LabMed Physical Activity Study. Funding This study was supported by the Portuguese Foundation for Science and Technology (FCT) grants: SFRH/BD/88984/2012 and UID/DTP/00617/2013; Research Centre in Physical Activity, Health and Leisure (CIAFEL), Faculty of Sport—University of Porto—Portugal. R.S. has a Discovery Early Career Research Award from the Australian Research Council (DE150101921). C.A.-S. is supported by a Doctoral Scholarship from Brazilian government by CAPES (Coordination of Improvement of Higher Education Personnel) (Proc: 9588-13-2). Conflicts of interest: None declared. Key points Aside from the effects on biological parameters, the consideration of associations between physical fitness with psychosocial aspects of health should be taken into account. 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Journal

The European Journal of Public HealthOxford University Press

Published: Mar 26, 2018

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