Vitamin D status of female UAE college students and associated risk factors

Vitamin D status of female UAE college students and associated risk factors Abstract Objective Vitamin D deficiency is now recognized as a pandemic with implications for bone health and chronic diseases. The study investigated the vitamin D status and risk factors of subnormal serum vitamin D levels in female college students. Design Cross-sectional study. Setting American University of Sharjah, United Arab Emirate. Serum 25-hydroxyvitamin D (25(OH)D) levels were measured for the participating female undergraduate college students using a radioimmunoassay kit. All participants answered a questionnaire that included 30 questions, which covered among others the demographic information, dietary intake, sun exposure and autoimmune diseases. Subjects Undergraduate college female students (n, 480), aged 18–26 years. Results Overall, 47.92% had suboptimal serum vitamin D levels. Results indicated that vitamin D deficiency and other health problems are prevalent among female university students. Risk factors included: wearing hijab by 37.5% of the students that might have interfered with the penetration of UVB radiation into the skin, short time sun exposure, use of sunscreens and limited intake of foods rich in vitamin D. Conclusions Vitamin D deficiency is a problem in female college students due to lifestyle, and avoidance of sun exposure. Poor vitamin D status has been associated with increased risk for development of several autoimmune diseases, and other health conditions. This problem needs to be addressed, where prevention of future health consequences in this young group is still possible. autoimmune diseases, female college students, health consequences, risk factors, vitamin D deficiency Introduction Vitamin D deficiency has emerged as a significant public health problem worldwide. Vitamin D is known as an essential factor involved in different immune functions besides skeletal and muscle development.1,2 The liver and the kidney have been established as the major sources of 25OHD production from vitamin D, and the circulating levels of 1,25(OH)2D, respectively.3 This vitamin is fat soluble consists of two bioequivalent forms that are biologically inert and must be activated in the body by undergoing two hydroxylations. The first hydroxylation occurs in the liver, which converts vitamin D to calcidiol (25-hydroxy-vitamin D), the biologically active form; that circulates in the blood and is the commonly assessed form in serum.4 The second hydroxylation produces calcitriol (1,25-dihydroxyvitamin D), the physiologically active form and occurs primarily in the kidney.5,6 Vitamin D facilitates the intestinal absorption of calcium by mediating active calcium transport across the intestinal mucosa. Vitamin D deficiency is most often associated with inadequate calcium intakes and causes bone degeneration or osteoporosis.7 Although, the United Arab Emirates is one of the sunniest regions in the world, vitamin D deficiency in the UAE residents (50–90%) is one of the highest in the world.8,9 The causes of vitamin D deficiency and the factors that may increase the risk for low vitamin D among the Middle Eastern population remain uncertain. Vitamin D deficiency is on the increase because of lower intakes of vitamin D fortified foods, reduced intakes of calcium rich foods, increased use of sun block along with decreased exposure to sunlight, decreased ultraviolet light exposure4 and obesity.10 Moreover, female sex, darker skin pigmentation and dietary habits are the main factors that are significantly associated with lower 25(OH)D levels.8 Numerous studies reported on the association between vitamin D and different health outcomes, however, fewer studies have addressed young adults.11,12 Many young adults drink carbonated beverages instead of milk, thereby decreasing the intake of both calcium and vitamin D and potentially increasing the risk of fracture.13 University students have more freedom and control over their lifestyles than prior to attending school, which makes the university years an appropriate time to develop healthy lifestyle patterns and behaviors.14 Most university students are interested in learning about nutrition15 to enhance their dietary habits16 and are at an ideal age to start a long-term positive change regarding vitamin D. Therefore, this age group should be a primary target for vitamin D deficiency prevention and intervention programs that promote their long-term health and protect them from disease development later in life.17 Recent studies have shown that vitamin D receptor, was present in almost all immune cells and some of its polymorphisms were found to be associated with increased incidence of autoimmune diseases. These findings led to a proposed link between vitamin D deficiency and autoimmune diseases.18 The purpose of the study was to evaluate the prevalence of vitamin D deficiency and possible risk factors influencing the vitamin D serum levels in college-aged students prior to the end of peak bone formation years (between the ages of 16 and 3019,20). Information about the status of this vitamin may help to inform politicians and health service managers regarding possible preventative health measures for this population. Methodology Participants and procedures Ethical approval for the study was obtained from the University Institutional Review Board. The purpose of the study was explained to participants and no identifying information was requested from the participants. This study was conducted in the American University of Sharjah, UAE. Serum vitamin D 25(OH)D status and vitamin D intake were examined for 480 female students’ aged 18–26 years. Students were recruited to participate in the study by sending an e-mail invitation or by classes. Students who responded to the e-mail between January and May and the students who fulfilled the inclusion criteria were enrolled in the study. Inclusion criteria was college female undergraduate English-speaking students aged 18–26 and willingness to complete the questionnaire and provide serum 25(OH)D test results. The students were informed that participation is voluntary, all responses will be anonymous and would remain confidential, and that participation in the survey implied consent. Data collection and study variables The main method of data collection was a questionnaire that consisted of three parts (total of 30 questions) as follows: first part was demographic information, e.g. age, gender, weight, height and race. Second part was sun exposure questions such as participant’s time exposure to the sun, and use of sunscreen. Since vitamin D is fat soluble, the third part was dietary questions to assess the dairy intake (milk and cheese) and other foods such as oils, eggs and fish (fresh, frozen, canned tuna or sardines). Questions regarding autoimmune diseases of the participants and/or their families were also included. The following definitions were included in the questionnaire for the students to understand before they answer: Autoimmunity: The body’s immune system attacks and destroys healthy body tissue. Chronic fatigue: Extreme fatigue or tiredness that does not go away with rest, and cannot be explained by an underlying medical condition. Body mass index (BMI): The weight in kilograms divided by height in meters squared (kg/m2). Following the World Health Organization21 classification, BMI ≤ 18.5 is considered underweight, a BMI ≥ 25 was considered overweight, while above 30 was considered obese. Serum 25(OH)D levels were measured using a radioimmunoassay kit (BioSource, Brussels, Belgium). A normal serum level of vitamin D was defined as a 25(OH)D concentration >20 ng/mL, and vitamin D insufficiency as serum 25(OH)D < 20 ng/ml (50 nmol/L),21 while <10 ng/mL was considered as severe deficiency.22 Data analyses All questionnaires were entered in an excel data spread sheet using Minitab 17, Tally individual variables. Descriptive statistics were computed for demographic data (age; sex). Data for continuous variables were summarized as means and standard deviation (SD) and as percentages for categorical variables (BMI, sun exposure, SPF use, food intake and the presence of other related health conditions). The symptoms reported by students with vitamin D deficiency were compared to those reported by students who had normal serum levels using unpaired t-test. Reported P values were two-sided, and P value < 0.05 was considered statistically significant. Results Vitamin D and risk factors A total of 230 (47.92%) students had vitamin D deficiency. Only (22.9%) of the affected students were taking vitamin D supplements. Baseline characteristics of the participating students were: age (years): 20.19 ± 1.82, BMI (kg/m2): 22.33 ± 3.47 and serum 25 (OH)D (ng/mL): 21.67 ± 9.5. Based on the WHO BMI, 14.6% of the students were considered overweight (BMI of 25–30), while 4.2% were considered obese (BMI over 30). Out of the 480 students, 180 (37.5%) were wearing hijab for religious or cultural reasons. The 180 students had subnormal serum 25 (OH)D levels (<20 ng/ml) and they complained of: tiredness (55), low mood (35), chronic fatigue (34), muscle weakness (26), bone pain (26), backaches (22), head sweating (10) and joint stiffness (9). The mean serum 25(OH)D values of students with western dress style differed significantly from that of students wearing Hijab (P ≤ 0.0001) by t-test (Table 1). The latest group also had less outdoor activity. The students’ outdoor daily sun exposure was as follows: 39.58% had 15–30 min exposure, while wearing a T shirt and trousers with few exceptions during the sun exposure. The sun exposure in 47.92% of the students was mainly between 10 am and 1 pm, 35.42% were exposed more than 30 min, while 25% avoided sun exposure with daily exposure for <15 min, and 35.42% of the students used sunscreen with variable sun protection factor (SPF of 25–100). Table 1 Prevalence of low vitamin D 25(OH)D (<20 ng/ml) by female dress style Dress style (n)  Total  Subnormal vitamin D (n)  Mean ± SD  P value*  Prevalence of low vitamin D (%)  Hijab (180)  180  180  18 ± 8  0.0001  37.5  Western dress style (300)  300  50  21.67 ± 9.5    16.7  Dress style (n)  Total  Subnormal vitamin D (n)  Mean ± SD  P value*  Prevalence of low vitamin D (%)  Hijab (180)  180  180  18 ± 8  0.0001  37.5  Western dress style (300)  300  50  21.67 ± 9.5    16.7  *The mean serum 25(OH)D values for students wearing western dress style differed significantly from that of students wearing Hijab (P = 0.0001). View Large Table 1 Prevalence of low vitamin D 25(OH)D (<20 ng/ml) by female dress style Dress style (n)  Total  Subnormal vitamin D (n)  Mean ± SD  P value*  Prevalence of low vitamin D (%)  Hijab (180)  180  180  18 ± 8  0.0001  37.5  Western dress style (300)  300  50  21.67 ± 9.5    16.7  Dress style (n)  Total  Subnormal vitamin D (n)  Mean ± SD  P value*  Prevalence of low vitamin D (%)  Hijab (180)  180  180  18 ± 8  0.0001  37.5  Western dress style (300)  300  50  21.67 ± 9.5    16.7  *The mean serum 25(OH)D values for students wearing western dress style differed significantly from that of students wearing Hijab (P = 0.0001). View Large Reported symptoms The most common symptoms reported by the students with vitamin D deficiency were given in Table 2 and Fig. 1. Table 2 Symptoms reported by students with serum 25(OH)D deficiency (n = 230) compared to students with normal levels (n = 250) Reported symptoms  Students with deficiency, n (%)*  Students with normal levels, n (%)  Tiredness  84 (36.52)  7 (2.8)  Low mood  51 (22.17)  2 (0.8)  Chronic fatigue  48 (20. 87)  2 (0.8)  Bone pain  39 (17.0)  1 (0.4)  Backaches  36 (15.65)  1 (0.4)  Sun sensitivity  34 (14.78)  2 (0.8)  Muscle weakness  33 (14.35)  1 (0.4)  Joint stiffness  28 (12.17)  1 (0.4)  Head sweating  21 (9.13)  0 (0.0)  Skin that easily bruises  15 (6. 52)  0 (0.0)  Vertigo  10 (4.35)  0 (0.0)  Unexplained rib and/or spinal column fractures  8 (3.48)  0 (0.0)  Loss of hair in eyebrow  8 (3.48)  0 (0.0)  Reported symptoms  Students with deficiency, n (%)*  Students with normal levels, n (%)  Tiredness  84 (36.52)  7 (2.8)  Low mood  51 (22.17)  2 (0.8)  Chronic fatigue  48 (20. 87)  2 (0.8)  Bone pain  39 (17.0)  1 (0.4)  Backaches  36 (15.65)  1 (0.4)  Sun sensitivity  34 (14.78)  2 (0.8)  Muscle weakness  33 (14.35)  1 (0.4)  Joint stiffness  28 (12.17)  1 (0.4)  Head sweating  21 (9.13)  0 (0.0)  Skin that easily bruises  15 (6. 52)  0 (0.0)  Vertigo  10 (4.35)  0 (0.0)  Unexplained rib and/or spinal column fractures  8 (3.48)  0 (0.0)  Loss of hair in eyebrow  8 (3.48)  0 (0.0)  *P value = 0.0001, the mean values of the above variables in the students with subnormal vitamin D differed significantly from that of students with normal levels. Table 2 Symptoms reported by students with serum 25(OH)D deficiency (n = 230) compared to students with normal levels (n = 250) Reported symptoms  Students with deficiency, n (%)*  Students with normal levels, n (%)  Tiredness  84 (36.52)  7 (2.8)  Low mood  51 (22.17)  2 (0.8)  Chronic fatigue  48 (20. 87)  2 (0.8)  Bone pain  39 (17.0)  1 (0.4)  Backaches  36 (15.65)  1 (0.4)  Sun sensitivity  34 (14.78)  2 (0.8)  Muscle weakness  33 (14.35)  1 (0.4)  Joint stiffness  28 (12.17)  1 (0.4)  Head sweating  21 (9.13)  0 (0.0)  Skin that easily bruises  15 (6. 52)  0 (0.0)  Vertigo  10 (4.35)  0 (0.0)  Unexplained rib and/or spinal column fractures  8 (3.48)  0 (0.0)  Loss of hair in eyebrow  8 (3.48)  0 (0.0)  Reported symptoms  Students with deficiency, n (%)*  Students with normal levels, n (%)  Tiredness  84 (36.52)  7 (2.8)  Low mood  51 (22.17)  2 (0.8)  Chronic fatigue  48 (20. 87)  2 (0.8)  Bone pain  39 (17.0)  1 (0.4)  Backaches  36 (15.65)  1 (0.4)  Sun sensitivity  34 (14.78)  2 (0.8)  Muscle weakness  33 (14.35)  1 (0.4)  Joint stiffness  28 (12.17)  1 (0.4)  Head sweating  21 (9.13)  0 (0.0)  Skin that easily bruises  15 (6. 52)  0 (0.0)  Vertigo  10 (4.35)  0 (0.0)  Unexplained rib and/or spinal column fractures  8 (3.48)  0 (0.0)  Loss of hair in eyebrow  8 (3.48)  0 (0.0)  *P value = 0.0001, the mean values of the above variables in the students with subnormal vitamin D differed significantly from that of students with normal levels. Fig. 1 View largeDownload slide Symptoms reported by students with serum 25(OH)D deficiency compared to students with normal levels. Fig. 1 View largeDownload slide Symptoms reported by students with serum 25(OH)D deficiency compared to students with normal levels. Tiredness (36.52%), low mode (22.17%) chronic fatigue (20. 87%), bone pain (17%) and backaches (15.65) compared to 0.4–2.8% of the students with normal serum 25(OH)D values. Autoimmune diseases Regarding a family member with autoimmune disease, 80% of the students answered ‘don’t know’. However, 10.42% reported a mother with rheumatoid arthritis, and one student reported a brother with diabetes type 1. Other health conditions reported only by students with vitamin D deficiency are shown in Table 3. Table 3 Health conditions reported only in students with vitamin D deficiency (n = 230)   n (%)  Autoimmune diseases   Psoriasis  9 (3.9)   Diabetes type 1  5 (2.2)  Other health conditions     Lactose intolerance  9 (3.9)   Anemia  9 (3.9)   Eating disorder  7 (4.04)   Thyroid disorders  5 (2.2)   Scoliosis  3 (1.3)   Cystic fibrosis  1 (0.4)    n (%)  Autoimmune diseases   Psoriasis  9 (3.9)   Diabetes type 1  5 (2.2)  Other health conditions     Lactose intolerance  9 (3.9)   Anemia  9 (3.9)   Eating disorder  7 (4.04)   Thyroid disorders  5 (2.2)   Scoliosis  3 (1.3)   Cystic fibrosis  1 (0.4)  View Large Table 3 Health conditions reported only in students with vitamin D deficiency (n = 230)   n (%)  Autoimmune diseases   Psoriasis  9 (3.9)   Diabetes type 1  5 (2.2)  Other health conditions     Lactose intolerance  9 (3.9)   Anemia  9 (3.9)   Eating disorder  7 (4.04)   Thyroid disorders  5 (2.2)   Scoliosis  3 (1.3)   Cystic fibrosis  1 (0.4)    n (%)  Autoimmune diseases   Psoriasis  9 (3.9)   Diabetes type 1  5 (2.2)  Other health conditions     Lactose intolerance  9 (3.9)   Anemia  9 (3.9)   Eating disorder  7 (4.04)   Thyroid disorders  5 (2.2)   Scoliosis  3 (1.3)   Cystic fibrosis  1 (0.4)  View Large Dietary intake The 87% of participants often consumed more than one of vitamin D food sources and were knowledgeable about health importance of vitamin D. The intake of foods rich in vitamin D of students with deficiency was as follows: 21% did not drink milk, 22.92% did not eat eggs, 45.3% did not eat fishes, while 8.3% did not eat dairy products, eggs or fishes. While intake of foods rich in vitamin D of students with normal levels were: 10% did not drink milk, 12% did not eat eggs, 18% did not eat fishes, while 2% did not eat dairy products, eggs or fishes. The mean serum 25(OH)D values of students who consumed foods rich in vitamin D differed significantly from that of students who did not (P ≤ 0.000). Discussion Main finding of this study This is the first study to report on vitamin D status, and risk factors in female college students in Sharjah, UAE. Serum 25(OH)D deficiencies were recorded for 47.92% of the students. The study suggested that subnormal vitamin D status is considerably more common in this population than previously thought, especially in students wearing hijab (modern headscarf) (37.5%), which might have interfered with the penetration of UVB radiation into the skin. It highlighted the risk factors and symptoms that are related to subnormal vitamin D levels. Overweight was recorded in 14.6% of the students, while 4.2% were obese. Vitamin D deficiency was common in overweight and obese individuals explained by the increase in the metabolic clearance of vitamin D in obesity, possibly due to enhanced uptake by adipose tissue.23 A higher BMI value of ≥30 and subcutaneous adipose tissue was associated with lower 1,25(OH)D,24 suggesting a more complex relationship than vitamin D bioavailability by uptake. Obese people may need larger than usual intakes of vitamin D to achieve 25(OH)D levels comparable to those of normal weight,4 because subcutaneous fat sequester more of the vitamin and alter its release into the circulation. The muscle weakness reported by 14. The 14.35% of the students with vitamin D deficiency (Table 1) might be due to the fact that vitamin D receptors are located on the fast-twitch muscle fibers, which are the first to respond in a fall.24 However, the deficiency is reversible with supplementation.25 Psoriasis and autoimmune diseases were reported by 3.9 and 2.2%, respectively, of the students with deficiency. Cumulative data have implicated vitamin D deficiency in the pathophysiology of psoriasis,26 and autoimmune thyroid disease.27 Human vitamin D supplementation studies have shown beneficial effects of this vitamin on immune function, in particular in the context of autoimmunity and the inbuilt tolerance mechanisms of dendritic cells.28 An association of vitamin D deficiency and a risk of anemia as reported by 3.9% students with deficiency (Table 2) had been previously established.29 Scoliosis, a sideways curvature of the spine that occurs most often during the growth spurt just before puberty was reported by three (1.3%) vitamin D-deficient students. Some studies have suggested that a decrease in bone mineral density associated with vitamin D suboptimal levels may be responsible for the appearance and progression of this disease.30 The study would generate interest of the public, health educators and health practitioners to consider vitamin D deficiency regarding possible preventative measures in this age group. What is already known Studies of university students at Abu Dhabi, UAE31 and in Sheraz, Iran, indicated that more than half of female students were vitamin D insufficient and 44% were vitamin D deficient.32 In the UAE, few vitamin D fortified foods are available in the market because there is no law that mandates the fortification of essential foods with vitamin D;33 which might contribute to hypovitaminosis D among the residents. A dietary intake assessment of students in the UAE confirmed that more than 70% of the female students did not consume vitamin D-rich or fortified foods, which contributed to the high incidence of hypovitaminosis D.34 Although, some studies identified a wide range of risk factors for vitamin D deficiency, however, few studies on vitamin D deficiencies in female college students were conducted in the UAE. What this study adds The study demonstrates that vitamin D deficiency is prevalent among female university students. This problem is due to avoidance (37.5%) and/or limited exposure to the sunlight due to the high temperatures during the summer that sometimes exceed 40°C. These are among other factors considered important determinant of vitamin D status in the study subjects. The limited sun exposure of students wearing extensive clothing appears to play an important role in the subnormal vitamin D status in these students. Hypovitaminosis D was attributed mainly to reduced outdoor activities and reduced exposure to sunlight in Middle Eastern population.35 The time of sun exposure required for the production of ultraviolet B-induced vitamin D in the skin affects the cutaneous synthesis, depending on the ability of UVB rays to stimulate vitamin D production.36 The best time for sun exposure for optimal vitamin D synthesis at a minimal risk of cutaneous malignant melanoma (CMM), is between 10 am and 1 pm37 because the action spectrum for CMM is likely to be centered at longer wavelengths (UVA, 320–400 nm) than that of vitamin D generation (UVB, 280–320 nm). The use of sunscreens with variable sun protection factor (SPF 25–100) by 35.42% of the students might have been one of the risk factors. Studies indicated that using a sunscreen with SPF 8 on skin blocks the body’s ability to synthesize vitamin D by 92.5%, and SPF 15 blocks nearly 99% of body’s ability to make this vitamin.38–40 Subnormal serum 25 (OH)D levels were found in the students wearing covering and long clothing that might have interfered with the penetration of UVB radiation into the skin even when exposed to sun and affects the cutaneous synthesis of vitamin D3.38 Earlier studies have linked increased rates of vitamin D deficiency in girls wearing conservative clothes with a cover (‘hijab’).1,22,41,42 The vitamin D status in female students at Istanbul Medipol University, reported a higher prevalence of vitamin D deficiencies (55%) for covered students compared to 20% for uncovered students.43 Vitamin D deficiency were also common among veiled Turkish immigrant women living in Germany.44 Ultra-Orthodox Jewish women, who wear head cover, for religious reasons are at high risk of vitamin D deficiency and osteoporosis.45 Moreover, studies in sunny countries, where people may be covered up for religious or cultural reasons, found that 30–50% of adults and children were vitamin D-deficient.46,47 Studies in the UK have shown low vitamin D levels in Asian women particularly among those who cover most of their skin for ‘cultural reasons’. The problem first came to light in Bradford, which has one of the Muslim populations in Britain, where nearly one quarter of the population (24.7%) are Muslims.48 The National Health Service in UK started launching a campaign aimed at Muslim women, to encourage them to increase their vitamin D intake. Regarding intake of foods rich in vitamin D by students with deficiency, 21–45.3% of the students did not eat fishes, eggs or drink milk, and 8.3% did not eat any of the vitamin D-rich foods. A previous study reported that up to 47% of vitamin D intake may come from dietary supplements.49 The prevalence of vitamin D deficiency is likely to be more common in populations with a higher proportion of at-risk groups, and/or that have low consumption of foods rich in vitamin D and low use of vitamin D supplements.50 Some countries such as the United States and Canada, fortify dairy products with vitamin D. Therefore, the individual vitamin D dietary intake is highly dependent on nutritional habits, and the country’s fortification strategy. However, without supplementation, vitamin D status depends strongly on endogenous vitamin D production, which is influenced by factors such as genetic determinants51 and lifestyle. In the current study, 14.6% of the students were overweight (BMI of 25–30), while 4.2% were obese (BMI over 30). Vitamin D deficiency common in overweight and obese individuals is probably explained by the increase in the metabolic clearance of vitamin D in obesity, possibly due to enhanced uptake by adipose tissue.23 A BMI value of ≥30 and subcutaneous adipose tissue were associated with lower 1,25(OH)D,24 suggesting a more complex relationship than vitamin D bioavailability by uptake. Obese people may need larger than usual intakes of vitamin D to achieve 25(OH)D levels comparable to those of normal weight,4 because subcutaneous fat sequesters more of the vitamin and alters its release into the circulation. The muscle weakness reported by 14. The 14.35% of the students with vitamin D deficiency (Table 1) might be explained by the fact that vitamin D receptors are located on the fast-twitch muscle fibers, which are the first to respond in a fall.24 However, this deficiency is reversible with vitamin D supplementation .25 Psoriasis and an autoimmune disease reported by 3.9 and 2.2%, respectively, of the students with deficiencies. Cumulative data have implicated vitamin D deficiency in the pathophysiology of psoriasis,26 and in autoimmune thyroid disease.27 Human vitamin D supplementation studies have shown beneficial effects of this vitamin on immune function, in particular in the context of autoimmunity.28 An association of vitamin D deficiency and a greater risk of anemia reported by 3.9% students with deficiency (Table 2) had been previously established.29 Scoliosis, a sideways curvature of the spine that occurs most often during the growth spurt just before puberty was reported by 3 (1.3%) vitamin D-deficient students. Some studies have suggested that a decrease in bone mineral density associated with vitamin D suboptimal levels may be responsible for the appearance and progression of this disease.30 A main strength of this study is the uniformity of the studied age group (18–26 years) and uniform measurement of serum 25(OH)D by a single assay. Unlike previous studies, it determined several risk factors and symptoms related to subnormal vitamin D levels. In addition, the information was collected using a structured questionnaire that was self-completed so students had the time and freedom to individually answer the questions. Unlike the personal interviews, this method lowers the recall bias. Recording symptoms of vitamin D deficiency, the time of day when exposed to the sun would allow better identification of subjects at high risk since both season24 and time of day influence cutaneous vitamin D synthesis.37 The university population has become increasingly diverse as young people have become more mobile in UAE. However, these students are representative of the wider population in terms of their major socioeconomic status. Limitations of this study A potential weakness of the study is that although a variety of confounding factors have been included in the questionnaire, others may have been missing. Although, the current study identified a wide range of risk factors for vitamin D deficiency, the true increased risk for an individual exposed to numerous risk factors is unclear. Ideally, a larger study performed in one season would be advantageous to investigate the relationship between vitamin D deficiency and autoimmune diseases. Risks are assumed to be additive and factors combine randomly; therefore, more research into the prevalence of the main risk factors in this age group is needed to address these limitations, and to better understand how factors combine to increase risk. Conclusion Educational programs addressing vitamin D status, factors affecting vitamin D intake and health consequences of suboptimal vitamin D status, should target college-aged individuals to increase their awareness of the problem. 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Google Scholar PubMed  26 Orgaz-Molina J, Buendía-Eisman A, Arrabal-Polo MA et al.  . Deficiency of serum concentration of 25-hydroxyvitamin D in psoriatic patients: a case-control study. J Am Acad Dermatol  2012; 67: 931– 8. Google Scholar CrossRef Search ADS PubMed  27 Christine G. Vitamin D supplementation: an update. US Pharm  2010; 35: 58– 76. 28 Prietl B, Treiber G, Pieber TR et al.  . Vitamin D and immune function. Nutrients  2013; 5: 2502– 21. Google Scholar CrossRef Search ADS PubMed  29 Sim JJ, Lac PT, Liu IL et al.  . Vitamin D deficiency and anemia: a cross-sectional study. Ann Hematol  2010; 89: 447– 52. Google Scholar CrossRef Search ADS PubMed  30 Batista R, Martins DE, Hayashi LF et al.  . Association between vitamin D serum levels and adolescent idiopathic scoliosis. Scoliosis  2014; 9( Suppl 1): O45. Google Scholar CrossRef Search ADS   31 Al Anouti F, Thomas J, Abdel-Wareth L et al.  . Vitamin D deficiency and sun avoidance among university students at Abu Dhabi, United Arab Emirates. Dermatoendocrinol  2011; 3: 235– 9. Google Scholar CrossRef Search ADS PubMed  32 Faghih S, Abdolahzadeh M, Mohammadi M et al.  . Prevalence of vitamin D deficiency and its related factors among University students in Shiraz, Iran. Int J Prev Med  2014; 5: 796– 9. Google Scholar PubMed  33 Hwalla N, Al Dhaheri AS, Radwan H et al.  . The prevalence of micronutrient deficiencies and inadequacies in the Middle East and approaches to interventions. Nutrients  2017; 9: 229. Google Scholar CrossRef Search ADS   34 Muhairi SJ, Mehairi AE, Khouri AA et al.  . Vitamin D deficiency among healthy adolescents in Al Ain, United Arab Emirates. BMC Public Health  2013; 13: 33. Google Scholar CrossRef Search ADS PubMed  35 Christie FT, Mason L. Knowledge, attitude and practice regarding vitamin D deficiency among female students in Saudi Arabia: a qualitative exploration. Int J Rheum Dis  2011; 14( 3): e22– 9. Google Scholar CrossRef Search ADS PubMed  36 Kull M Jr, Kallikorm R, Tamm A et al.  . Seasonal variance of 25-(OH) vitamin D in the general population of Estonia, a Northern European country. BMC Public Health  2009; 9: 22. Google Scholar CrossRef Search ADS PubMed  37 Moan J, Grigalavicius M, Dahlback A et al.  . Ultraviolet-radiation and health: optimal time for sun exposure. Adv Exp Med Biol  2014; 810: 423– 8. Google Scholar PubMed  38 Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences. Am J Clin Nutr  2008; 87: 1080S– 6S. Google Scholar PubMed  39 Matsuoka LY, Ide L, Wortsmen J et al.  . Sunscreen suppress cutaneous vitamin D3 synthesis. J Clin Endocrinol Metab  1987; 64: 1165– 8. Google Scholar CrossRef Search ADS PubMed  40 Robinson JK. Sun exposure, sun protection, and vitamin D. J Am Med Assoc  2005; 294: 1541– 5. Google Scholar CrossRef Search ADS   41 Alshahrani AA. Vitamin D deficiency and possible risk factors among Middle Eastern university students in London, Ontario, Canada. Electronic Thesis and Dissertation Repository. 2014. 42 Lips P. Worldwide status of vitamin D nutrition. J Steroid Biochem Mol Biol  2010; 12: 297– 300. Google Scholar CrossRef Search ADS   43 Buyukuslu N, Esin K, Hizli H et al.  . Clothing preference affects vitamin D status of women. Nutr Res  2014; 34: 688– 93. Google Scholar CrossRef Search ADS PubMed  44 Erkal MZ, Wilde J, Bilgin Y et al.  . High prevalence of vitamin D deficiency, secondary hyperparathyroidism and generalized bone pain in Turkish immigrants in Germany: identification of risk factors. Osteoporos Int  2006; 17: 1133– 40. Google Scholar CrossRef Search ADS PubMed  45 Siegel-Itzkovich J. Ultra-Orthodox Jewish women at risk of vitamin D deficiency. Br Med J  2001; 323: 10. Google Scholar CrossRef Search ADS   46 Holick MF. Vitamin D deficiency. N Engl J Med  2007; 357: 266– 81. Google Scholar CrossRef Search ADS PubMed  47 Batieha A, Khader Y, Jaddou H et al.  . Vitamin D status in Jordan: dress style and gender discrepancies. Ann Nutr Metab  2011; 58: 10– 8. Google Scholar CrossRef Search ADS PubMed  48 https://www.bradford.gov.uk/open-data/our-datasets/population (5 November, date last accessed). 49 Tripkovic L, Lambert H, Hart K et al.  . Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr  2012; 95: 1357– 64. Google Scholar CrossRef Search ADS PubMed  50 Spiro A, Buttriss JL. Vitamin D: An overview of vitamin D status and intake in Europe. Nutr Bull  2014; 39: 322– 50. Google Scholar CrossRef Search ADS PubMed  51 Wang TJ, Zhang F, Richards JB et al.  . Common genetic determinants of vitamin D insufficiency: a genome-wide association study. Lancet  2010; 376: 180– 8. Google Scholar CrossRef Search ADS PubMed  © The Author(s) 2018. Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Public Health Oxford University Press

Vitamin D status of female UAE college students and associated risk factors

Journal of Public Health , Volume Advance Article – Jan 27, 2018

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Oxford University Press
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© The Author(s) 2018. Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com
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1741-3842
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10.1093/pubmed/fdy009
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Abstract

Abstract Objective Vitamin D deficiency is now recognized as a pandemic with implications for bone health and chronic diseases. The study investigated the vitamin D status and risk factors of subnormal serum vitamin D levels in female college students. Design Cross-sectional study. Setting American University of Sharjah, United Arab Emirate. Serum 25-hydroxyvitamin D (25(OH)D) levels were measured for the participating female undergraduate college students using a radioimmunoassay kit. All participants answered a questionnaire that included 30 questions, which covered among others the demographic information, dietary intake, sun exposure and autoimmune diseases. Subjects Undergraduate college female students (n, 480), aged 18–26 years. Results Overall, 47.92% had suboptimal serum vitamin D levels. Results indicated that vitamin D deficiency and other health problems are prevalent among female university students. Risk factors included: wearing hijab by 37.5% of the students that might have interfered with the penetration of UVB radiation into the skin, short time sun exposure, use of sunscreens and limited intake of foods rich in vitamin D. Conclusions Vitamin D deficiency is a problem in female college students due to lifestyle, and avoidance of sun exposure. Poor vitamin D status has been associated with increased risk for development of several autoimmune diseases, and other health conditions. This problem needs to be addressed, where prevention of future health consequences in this young group is still possible. autoimmune diseases, female college students, health consequences, risk factors, vitamin D deficiency Introduction Vitamin D deficiency has emerged as a significant public health problem worldwide. Vitamin D is known as an essential factor involved in different immune functions besides skeletal and muscle development.1,2 The liver and the kidney have been established as the major sources of 25OHD production from vitamin D, and the circulating levels of 1,25(OH)2D, respectively.3 This vitamin is fat soluble consists of two bioequivalent forms that are biologically inert and must be activated in the body by undergoing two hydroxylations. The first hydroxylation occurs in the liver, which converts vitamin D to calcidiol (25-hydroxy-vitamin D), the biologically active form; that circulates in the blood and is the commonly assessed form in serum.4 The second hydroxylation produces calcitriol (1,25-dihydroxyvitamin D), the physiologically active form and occurs primarily in the kidney.5,6 Vitamin D facilitates the intestinal absorption of calcium by mediating active calcium transport across the intestinal mucosa. Vitamin D deficiency is most often associated with inadequate calcium intakes and causes bone degeneration or osteoporosis.7 Although, the United Arab Emirates is one of the sunniest regions in the world, vitamin D deficiency in the UAE residents (50–90%) is one of the highest in the world.8,9 The causes of vitamin D deficiency and the factors that may increase the risk for low vitamin D among the Middle Eastern population remain uncertain. Vitamin D deficiency is on the increase because of lower intakes of vitamin D fortified foods, reduced intakes of calcium rich foods, increased use of sun block along with decreased exposure to sunlight, decreased ultraviolet light exposure4 and obesity.10 Moreover, female sex, darker skin pigmentation and dietary habits are the main factors that are significantly associated with lower 25(OH)D levels.8 Numerous studies reported on the association between vitamin D and different health outcomes, however, fewer studies have addressed young adults.11,12 Many young adults drink carbonated beverages instead of milk, thereby decreasing the intake of both calcium and vitamin D and potentially increasing the risk of fracture.13 University students have more freedom and control over their lifestyles than prior to attending school, which makes the university years an appropriate time to develop healthy lifestyle patterns and behaviors.14 Most university students are interested in learning about nutrition15 to enhance their dietary habits16 and are at an ideal age to start a long-term positive change regarding vitamin D. Therefore, this age group should be a primary target for vitamin D deficiency prevention and intervention programs that promote their long-term health and protect them from disease development later in life.17 Recent studies have shown that vitamin D receptor, was present in almost all immune cells and some of its polymorphisms were found to be associated with increased incidence of autoimmune diseases. These findings led to a proposed link between vitamin D deficiency and autoimmune diseases.18 The purpose of the study was to evaluate the prevalence of vitamin D deficiency and possible risk factors influencing the vitamin D serum levels in college-aged students prior to the end of peak bone formation years (between the ages of 16 and 3019,20). Information about the status of this vitamin may help to inform politicians and health service managers regarding possible preventative health measures for this population. Methodology Participants and procedures Ethical approval for the study was obtained from the University Institutional Review Board. The purpose of the study was explained to participants and no identifying information was requested from the participants. This study was conducted in the American University of Sharjah, UAE. Serum vitamin D 25(OH)D status and vitamin D intake were examined for 480 female students’ aged 18–26 years. Students were recruited to participate in the study by sending an e-mail invitation or by classes. Students who responded to the e-mail between January and May and the students who fulfilled the inclusion criteria were enrolled in the study. Inclusion criteria was college female undergraduate English-speaking students aged 18–26 and willingness to complete the questionnaire and provide serum 25(OH)D test results. The students were informed that participation is voluntary, all responses will be anonymous and would remain confidential, and that participation in the survey implied consent. Data collection and study variables The main method of data collection was a questionnaire that consisted of three parts (total of 30 questions) as follows: first part was demographic information, e.g. age, gender, weight, height and race. Second part was sun exposure questions such as participant’s time exposure to the sun, and use of sunscreen. Since vitamin D is fat soluble, the third part was dietary questions to assess the dairy intake (milk and cheese) and other foods such as oils, eggs and fish (fresh, frozen, canned tuna or sardines). Questions regarding autoimmune diseases of the participants and/or their families were also included. The following definitions were included in the questionnaire for the students to understand before they answer: Autoimmunity: The body’s immune system attacks and destroys healthy body tissue. Chronic fatigue: Extreme fatigue or tiredness that does not go away with rest, and cannot be explained by an underlying medical condition. Body mass index (BMI): The weight in kilograms divided by height in meters squared (kg/m2). Following the World Health Organization21 classification, BMI ≤ 18.5 is considered underweight, a BMI ≥ 25 was considered overweight, while above 30 was considered obese. Serum 25(OH)D levels were measured using a radioimmunoassay kit (BioSource, Brussels, Belgium). A normal serum level of vitamin D was defined as a 25(OH)D concentration >20 ng/mL, and vitamin D insufficiency as serum 25(OH)D < 20 ng/ml (50 nmol/L),21 while <10 ng/mL was considered as severe deficiency.22 Data analyses All questionnaires were entered in an excel data spread sheet using Minitab 17, Tally individual variables. Descriptive statistics were computed for demographic data (age; sex). Data for continuous variables were summarized as means and standard deviation (SD) and as percentages for categorical variables (BMI, sun exposure, SPF use, food intake and the presence of other related health conditions). The symptoms reported by students with vitamin D deficiency were compared to those reported by students who had normal serum levels using unpaired t-test. Reported P values were two-sided, and P value < 0.05 was considered statistically significant. Results Vitamin D and risk factors A total of 230 (47.92%) students had vitamin D deficiency. Only (22.9%) of the affected students were taking vitamin D supplements. Baseline characteristics of the participating students were: age (years): 20.19 ± 1.82, BMI (kg/m2): 22.33 ± 3.47 and serum 25 (OH)D (ng/mL): 21.67 ± 9.5. Based on the WHO BMI, 14.6% of the students were considered overweight (BMI of 25–30), while 4.2% were considered obese (BMI over 30). Out of the 480 students, 180 (37.5%) were wearing hijab for religious or cultural reasons. The 180 students had subnormal serum 25 (OH)D levels (<20 ng/ml) and they complained of: tiredness (55), low mood (35), chronic fatigue (34), muscle weakness (26), bone pain (26), backaches (22), head sweating (10) and joint stiffness (9). The mean serum 25(OH)D values of students with western dress style differed significantly from that of students wearing Hijab (P ≤ 0.0001) by t-test (Table 1). The latest group also had less outdoor activity. The students’ outdoor daily sun exposure was as follows: 39.58% had 15–30 min exposure, while wearing a T shirt and trousers with few exceptions during the sun exposure. The sun exposure in 47.92% of the students was mainly between 10 am and 1 pm, 35.42% were exposed more than 30 min, while 25% avoided sun exposure with daily exposure for <15 min, and 35.42% of the students used sunscreen with variable sun protection factor (SPF of 25–100). Table 1 Prevalence of low vitamin D 25(OH)D (<20 ng/ml) by female dress style Dress style (n)  Total  Subnormal vitamin D (n)  Mean ± SD  P value*  Prevalence of low vitamin D (%)  Hijab (180)  180  180  18 ± 8  0.0001  37.5  Western dress style (300)  300  50  21.67 ± 9.5    16.7  Dress style (n)  Total  Subnormal vitamin D (n)  Mean ± SD  P value*  Prevalence of low vitamin D (%)  Hijab (180)  180  180  18 ± 8  0.0001  37.5  Western dress style (300)  300  50  21.67 ± 9.5    16.7  *The mean serum 25(OH)D values for students wearing western dress style differed significantly from that of students wearing Hijab (P = 0.0001). View Large Table 1 Prevalence of low vitamin D 25(OH)D (<20 ng/ml) by female dress style Dress style (n)  Total  Subnormal vitamin D (n)  Mean ± SD  P value*  Prevalence of low vitamin D (%)  Hijab (180)  180  180  18 ± 8  0.0001  37.5  Western dress style (300)  300  50  21.67 ± 9.5    16.7  Dress style (n)  Total  Subnormal vitamin D (n)  Mean ± SD  P value*  Prevalence of low vitamin D (%)  Hijab (180)  180  180  18 ± 8  0.0001  37.5  Western dress style (300)  300  50  21.67 ± 9.5    16.7  *The mean serum 25(OH)D values for students wearing western dress style differed significantly from that of students wearing Hijab (P = 0.0001). View Large Reported symptoms The most common symptoms reported by the students with vitamin D deficiency were given in Table 2 and Fig. 1. Table 2 Symptoms reported by students with serum 25(OH)D deficiency (n = 230) compared to students with normal levels (n = 250) Reported symptoms  Students with deficiency, n (%)*  Students with normal levels, n (%)  Tiredness  84 (36.52)  7 (2.8)  Low mood  51 (22.17)  2 (0.8)  Chronic fatigue  48 (20. 87)  2 (0.8)  Bone pain  39 (17.0)  1 (0.4)  Backaches  36 (15.65)  1 (0.4)  Sun sensitivity  34 (14.78)  2 (0.8)  Muscle weakness  33 (14.35)  1 (0.4)  Joint stiffness  28 (12.17)  1 (0.4)  Head sweating  21 (9.13)  0 (0.0)  Skin that easily bruises  15 (6. 52)  0 (0.0)  Vertigo  10 (4.35)  0 (0.0)  Unexplained rib and/or spinal column fractures  8 (3.48)  0 (0.0)  Loss of hair in eyebrow  8 (3.48)  0 (0.0)  Reported symptoms  Students with deficiency, n (%)*  Students with normal levels, n (%)  Tiredness  84 (36.52)  7 (2.8)  Low mood  51 (22.17)  2 (0.8)  Chronic fatigue  48 (20. 87)  2 (0.8)  Bone pain  39 (17.0)  1 (0.4)  Backaches  36 (15.65)  1 (0.4)  Sun sensitivity  34 (14.78)  2 (0.8)  Muscle weakness  33 (14.35)  1 (0.4)  Joint stiffness  28 (12.17)  1 (0.4)  Head sweating  21 (9.13)  0 (0.0)  Skin that easily bruises  15 (6. 52)  0 (0.0)  Vertigo  10 (4.35)  0 (0.0)  Unexplained rib and/or spinal column fractures  8 (3.48)  0 (0.0)  Loss of hair in eyebrow  8 (3.48)  0 (0.0)  *P value = 0.0001, the mean values of the above variables in the students with subnormal vitamin D differed significantly from that of students with normal levels. Table 2 Symptoms reported by students with serum 25(OH)D deficiency (n = 230) compared to students with normal levels (n = 250) Reported symptoms  Students with deficiency, n (%)*  Students with normal levels, n (%)  Tiredness  84 (36.52)  7 (2.8)  Low mood  51 (22.17)  2 (0.8)  Chronic fatigue  48 (20. 87)  2 (0.8)  Bone pain  39 (17.0)  1 (0.4)  Backaches  36 (15.65)  1 (0.4)  Sun sensitivity  34 (14.78)  2 (0.8)  Muscle weakness  33 (14.35)  1 (0.4)  Joint stiffness  28 (12.17)  1 (0.4)  Head sweating  21 (9.13)  0 (0.0)  Skin that easily bruises  15 (6. 52)  0 (0.0)  Vertigo  10 (4.35)  0 (0.0)  Unexplained rib and/or spinal column fractures  8 (3.48)  0 (0.0)  Loss of hair in eyebrow  8 (3.48)  0 (0.0)  Reported symptoms  Students with deficiency, n (%)*  Students with normal levels, n (%)  Tiredness  84 (36.52)  7 (2.8)  Low mood  51 (22.17)  2 (0.8)  Chronic fatigue  48 (20. 87)  2 (0.8)  Bone pain  39 (17.0)  1 (0.4)  Backaches  36 (15.65)  1 (0.4)  Sun sensitivity  34 (14.78)  2 (0.8)  Muscle weakness  33 (14.35)  1 (0.4)  Joint stiffness  28 (12.17)  1 (0.4)  Head sweating  21 (9.13)  0 (0.0)  Skin that easily bruises  15 (6. 52)  0 (0.0)  Vertigo  10 (4.35)  0 (0.0)  Unexplained rib and/or spinal column fractures  8 (3.48)  0 (0.0)  Loss of hair in eyebrow  8 (3.48)  0 (0.0)  *P value = 0.0001, the mean values of the above variables in the students with subnormal vitamin D differed significantly from that of students with normal levels. Fig. 1 View largeDownload slide Symptoms reported by students with serum 25(OH)D deficiency compared to students with normal levels. Fig. 1 View largeDownload slide Symptoms reported by students with serum 25(OH)D deficiency compared to students with normal levels. Tiredness (36.52%), low mode (22.17%) chronic fatigue (20. 87%), bone pain (17%) and backaches (15.65) compared to 0.4–2.8% of the students with normal serum 25(OH)D values. Autoimmune diseases Regarding a family member with autoimmune disease, 80% of the students answered ‘don’t know’. However, 10.42% reported a mother with rheumatoid arthritis, and one student reported a brother with diabetes type 1. Other health conditions reported only by students with vitamin D deficiency are shown in Table 3. Table 3 Health conditions reported only in students with vitamin D deficiency (n = 230)   n (%)  Autoimmune diseases   Psoriasis  9 (3.9)   Diabetes type 1  5 (2.2)  Other health conditions     Lactose intolerance  9 (3.9)   Anemia  9 (3.9)   Eating disorder  7 (4.04)   Thyroid disorders  5 (2.2)   Scoliosis  3 (1.3)   Cystic fibrosis  1 (0.4)    n (%)  Autoimmune diseases   Psoriasis  9 (3.9)   Diabetes type 1  5 (2.2)  Other health conditions     Lactose intolerance  9 (3.9)   Anemia  9 (3.9)   Eating disorder  7 (4.04)   Thyroid disorders  5 (2.2)   Scoliosis  3 (1.3)   Cystic fibrosis  1 (0.4)  View Large Table 3 Health conditions reported only in students with vitamin D deficiency (n = 230)   n (%)  Autoimmune diseases   Psoriasis  9 (3.9)   Diabetes type 1  5 (2.2)  Other health conditions     Lactose intolerance  9 (3.9)   Anemia  9 (3.9)   Eating disorder  7 (4.04)   Thyroid disorders  5 (2.2)   Scoliosis  3 (1.3)   Cystic fibrosis  1 (0.4)    n (%)  Autoimmune diseases   Psoriasis  9 (3.9)   Diabetes type 1  5 (2.2)  Other health conditions     Lactose intolerance  9 (3.9)   Anemia  9 (3.9)   Eating disorder  7 (4.04)   Thyroid disorders  5 (2.2)   Scoliosis  3 (1.3)   Cystic fibrosis  1 (0.4)  View Large Dietary intake The 87% of participants often consumed more than one of vitamin D food sources and were knowledgeable about health importance of vitamin D. The intake of foods rich in vitamin D of students with deficiency was as follows: 21% did not drink milk, 22.92% did not eat eggs, 45.3% did not eat fishes, while 8.3% did not eat dairy products, eggs or fishes. While intake of foods rich in vitamin D of students with normal levels were: 10% did not drink milk, 12% did not eat eggs, 18% did not eat fishes, while 2% did not eat dairy products, eggs or fishes. The mean serum 25(OH)D values of students who consumed foods rich in vitamin D differed significantly from that of students who did not (P ≤ 0.000). Discussion Main finding of this study This is the first study to report on vitamin D status, and risk factors in female college students in Sharjah, UAE. Serum 25(OH)D deficiencies were recorded for 47.92% of the students. The study suggested that subnormal vitamin D status is considerably more common in this population than previously thought, especially in students wearing hijab (modern headscarf) (37.5%), which might have interfered with the penetration of UVB radiation into the skin. It highlighted the risk factors and symptoms that are related to subnormal vitamin D levels. Overweight was recorded in 14.6% of the students, while 4.2% were obese. Vitamin D deficiency was common in overweight and obese individuals explained by the increase in the metabolic clearance of vitamin D in obesity, possibly due to enhanced uptake by adipose tissue.23 A higher BMI value of ≥30 and subcutaneous adipose tissue was associated with lower 1,25(OH)D,24 suggesting a more complex relationship than vitamin D bioavailability by uptake. Obese people may need larger than usual intakes of vitamin D to achieve 25(OH)D levels comparable to those of normal weight,4 because subcutaneous fat sequester more of the vitamin and alter its release into the circulation. The muscle weakness reported by 14. The 14.35% of the students with vitamin D deficiency (Table 1) might be due to the fact that vitamin D receptors are located on the fast-twitch muscle fibers, which are the first to respond in a fall.24 However, the deficiency is reversible with supplementation.25 Psoriasis and autoimmune diseases were reported by 3.9 and 2.2%, respectively, of the students with deficiency. Cumulative data have implicated vitamin D deficiency in the pathophysiology of psoriasis,26 and autoimmune thyroid disease.27 Human vitamin D supplementation studies have shown beneficial effects of this vitamin on immune function, in particular in the context of autoimmunity and the inbuilt tolerance mechanisms of dendritic cells.28 An association of vitamin D deficiency and a risk of anemia as reported by 3.9% students with deficiency (Table 2) had been previously established.29 Scoliosis, a sideways curvature of the spine that occurs most often during the growth spurt just before puberty was reported by three (1.3%) vitamin D-deficient students. Some studies have suggested that a decrease in bone mineral density associated with vitamin D suboptimal levels may be responsible for the appearance and progression of this disease.30 The study would generate interest of the public, health educators and health practitioners to consider vitamin D deficiency regarding possible preventative measures in this age group. What is already known Studies of university students at Abu Dhabi, UAE31 and in Sheraz, Iran, indicated that more than half of female students were vitamin D insufficient and 44% were vitamin D deficient.32 In the UAE, few vitamin D fortified foods are available in the market because there is no law that mandates the fortification of essential foods with vitamin D;33 which might contribute to hypovitaminosis D among the residents. A dietary intake assessment of students in the UAE confirmed that more than 70% of the female students did not consume vitamin D-rich or fortified foods, which contributed to the high incidence of hypovitaminosis D.34 Although, some studies identified a wide range of risk factors for vitamin D deficiency, however, few studies on vitamin D deficiencies in female college students were conducted in the UAE. What this study adds The study demonstrates that vitamin D deficiency is prevalent among female university students. This problem is due to avoidance (37.5%) and/or limited exposure to the sunlight due to the high temperatures during the summer that sometimes exceed 40°C. These are among other factors considered important determinant of vitamin D status in the study subjects. The limited sun exposure of students wearing extensive clothing appears to play an important role in the subnormal vitamin D status in these students. Hypovitaminosis D was attributed mainly to reduced outdoor activities and reduced exposure to sunlight in Middle Eastern population.35 The time of sun exposure required for the production of ultraviolet B-induced vitamin D in the skin affects the cutaneous synthesis, depending on the ability of UVB rays to stimulate vitamin D production.36 The best time for sun exposure for optimal vitamin D synthesis at a minimal risk of cutaneous malignant melanoma (CMM), is between 10 am and 1 pm37 because the action spectrum for CMM is likely to be centered at longer wavelengths (UVA, 320–400 nm) than that of vitamin D generation (UVB, 280–320 nm). The use of sunscreens with variable sun protection factor (SPF 25–100) by 35.42% of the students might have been one of the risk factors. Studies indicated that using a sunscreen with SPF 8 on skin blocks the body’s ability to synthesize vitamin D by 92.5%, and SPF 15 blocks nearly 99% of body’s ability to make this vitamin.38–40 Subnormal serum 25 (OH)D levels were found in the students wearing covering and long clothing that might have interfered with the penetration of UVB radiation into the skin even when exposed to sun and affects the cutaneous synthesis of vitamin D3.38 Earlier studies have linked increased rates of vitamin D deficiency in girls wearing conservative clothes with a cover (‘hijab’).1,22,41,42 The vitamin D status in female students at Istanbul Medipol University, reported a higher prevalence of vitamin D deficiencies (55%) for covered students compared to 20% for uncovered students.43 Vitamin D deficiency were also common among veiled Turkish immigrant women living in Germany.44 Ultra-Orthodox Jewish women, who wear head cover, for religious reasons are at high risk of vitamin D deficiency and osteoporosis.45 Moreover, studies in sunny countries, where people may be covered up for religious or cultural reasons, found that 30–50% of adults and children were vitamin D-deficient.46,47 Studies in the UK have shown low vitamin D levels in Asian women particularly among those who cover most of their skin for ‘cultural reasons’. The problem first came to light in Bradford, which has one of the Muslim populations in Britain, where nearly one quarter of the population (24.7%) are Muslims.48 The National Health Service in UK started launching a campaign aimed at Muslim women, to encourage them to increase their vitamin D intake. Regarding intake of foods rich in vitamin D by students with deficiency, 21–45.3% of the students did not eat fishes, eggs or drink milk, and 8.3% did not eat any of the vitamin D-rich foods. A previous study reported that up to 47% of vitamin D intake may come from dietary supplements.49 The prevalence of vitamin D deficiency is likely to be more common in populations with a higher proportion of at-risk groups, and/or that have low consumption of foods rich in vitamin D and low use of vitamin D supplements.50 Some countries such as the United States and Canada, fortify dairy products with vitamin D. Therefore, the individual vitamin D dietary intake is highly dependent on nutritional habits, and the country’s fortification strategy. However, without supplementation, vitamin D status depends strongly on endogenous vitamin D production, which is influenced by factors such as genetic determinants51 and lifestyle. In the current study, 14.6% of the students were overweight (BMI of 25–30), while 4.2% were obese (BMI over 30). Vitamin D deficiency common in overweight and obese individuals is probably explained by the increase in the metabolic clearance of vitamin D in obesity, possibly due to enhanced uptake by adipose tissue.23 A BMI value of ≥30 and subcutaneous adipose tissue were associated with lower 1,25(OH)D,24 suggesting a more complex relationship than vitamin D bioavailability by uptake. Obese people may need larger than usual intakes of vitamin D to achieve 25(OH)D levels comparable to those of normal weight,4 because subcutaneous fat sequesters more of the vitamin and alters its release into the circulation. The muscle weakness reported by 14. The 14.35% of the students with vitamin D deficiency (Table 1) might be explained by the fact that vitamin D receptors are located on the fast-twitch muscle fibers, which are the first to respond in a fall.24 However, this deficiency is reversible with vitamin D supplementation .25 Psoriasis and an autoimmune disease reported by 3.9 and 2.2%, respectively, of the students with deficiencies. Cumulative data have implicated vitamin D deficiency in the pathophysiology of psoriasis,26 and in autoimmune thyroid disease.27 Human vitamin D supplementation studies have shown beneficial effects of this vitamin on immune function, in particular in the context of autoimmunity.28 An association of vitamin D deficiency and a greater risk of anemia reported by 3.9% students with deficiency (Table 2) had been previously established.29 Scoliosis, a sideways curvature of the spine that occurs most often during the growth spurt just before puberty was reported by 3 (1.3%) vitamin D-deficient students. Some studies have suggested that a decrease in bone mineral density associated with vitamin D suboptimal levels may be responsible for the appearance and progression of this disease.30 A main strength of this study is the uniformity of the studied age group (18–26 years) and uniform measurement of serum 25(OH)D by a single assay. Unlike previous studies, it determined several risk factors and symptoms related to subnormal vitamin D levels. In addition, the information was collected using a structured questionnaire that was self-completed so students had the time and freedom to individually answer the questions. Unlike the personal interviews, this method lowers the recall bias. Recording symptoms of vitamin D deficiency, the time of day when exposed to the sun would allow better identification of subjects at high risk since both season24 and time of day influence cutaneous vitamin D synthesis.37 The university population has become increasingly diverse as young people have become more mobile in UAE. However, these students are representative of the wider population in terms of their major socioeconomic status. Limitations of this study A potential weakness of the study is that although a variety of confounding factors have been included in the questionnaire, others may have been missing. Although, the current study identified a wide range of risk factors for vitamin D deficiency, the true increased risk for an individual exposed to numerous risk factors is unclear. Ideally, a larger study performed in one season would be advantageous to investigate the relationship between vitamin D deficiency and autoimmune diseases. Risks are assumed to be additive and factors combine randomly; therefore, more research into the prevalence of the main risk factors in this age group is needed to address these limitations, and to better understand how factors combine to increase risk. Conclusion Educational programs addressing vitamin D status, factors affecting vitamin D intake and health consequences of suboptimal vitamin D status, should target college-aged individuals to increase their awareness of the problem. 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Published by Oxford University Press on behalf of Faculty of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com

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Journal of Public HealthOxford University Press

Published: Jan 27, 2018

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