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Is Sitting Harmful to Health? It Is Too Early to Say—Reply

Is Sitting Harmful to Health? It Is Too Early to Say—Reply In reply The responses to our recent article on sitting time and mortality1 highlight the interest in, and potential importance of, sedentary behaviors and health. Our original article found that prolonged sitting was associated with increased all-cause mortality risk, independent of physical activity.1 A study limitation was the relatively short follow-up time (mean, 2.8 years), potentially leading to confounding by occult disease. However, findings persisted after adjustments (for demographic variables, physical activity, body mass index, smoking, self-rated health, and disability), chronic disease stratification, and sensitivity analyses excluding deaths in the first year. Nevertheless, neither reverse causality due to occult disease nor residual confounding could be completely excluded.1 The correspondents suggest additional potential sources of confounding and reverse causality from occupational factors including “exposure to airborne particulates and incidence of stroke; occupational stress and cardiovascular disease; occupational cancer-related mortality”; and poor diet. Although these factors might hypothetically play a role in the relationship between sitting and mortality, our study considered total sitting time and not “occupational sitting time.” Moreover, only 49% of participants in the study were in paid work. Nonoccupational sedentary behaviors (especially television viewing) have been shown to be associated with all-cause mortality,1,2 making the proposed residual confounding less likely. Furthermore, a recent similar study with an 8.5-year follow-up showed that sitting for 9 hours per day or more was associated with an all-cause mortality hazard ratio of 1.19 (95% CI, 1.12-1.27) compared with people sitting less than 3 hours per day, after extensive adjustment for confounding, including diet quality; excluding deaths in the first 3 years of follow-up suggested no evidence of reverse causality.3 Importantly, other research has suggested plausible physiological mechanisms for the detrimental effects of prolonged sitting, and findings from intervention studies indicate metabolic benefits from reductions in time spent sitting.1,4 Finally, the substantial difference between the unadjusted population attributable fraction (20.9%) calculated by Peterson and colleagues in their letter, and our adjusted population attributable fraction (6.9%)1 illustrates the importance of adjustment for confounders and suggests caution in the interpretation of unadjusted attributable risks. Our study is one piece in the accumulating evidence that prolonged sitting may be detrimental to health. It is unclear if and when this evidence will become sufficient to warrant widespread changes in policy and behavior. We agree that achieving far-reaching change is likely to be challenging, but not impossible, especially when such important health outcomes are at stake. Back to top Article Information Correspondence: Dr van der Ploeg, Department of Public and Occupational Health, VU University Medical Center Amsterdam, van der Boechorststraat 7, 1081BT Amsterdam, the Netherlands (hp.vanderploeg@vumc.nl). Financial Disclosure: None reported. Additional Contributions: Tien Chey, MAS, and Rosemary Korda, PhD, assisted with the preparation of this letter to the editor. References 1. van der Ploeg HP, Chey T, Korda RJ, Banks E, Bauman A. Sitting time and all-cause mortality risk in 222 497 Australian adults. Arch Intern Med. 2012;172(6):494-50022450936PubMedGoogle ScholarCrossref 2. Grøntved A, Hu FB. Television viewing and risk of type 2 diabetes, cardiovascular disease, and all-cause mortality: a meta-analysis. JAMA. 2011;305(23):2448-245521673296PubMedGoogle Scholar 3. Matthews CE, George SM, Moore SC, et al. Amount of time spent in sedentary behaviors and cause-specific mortality in US adults. Am J Clin Nutr. 2012;95(2):437-44522218159PubMedGoogle Scholar 4. Dunstan DW, Kingwell BA, Larsen R, et al. Breaking up prolonged sitting reduces postprandial glucose and insulin responses. Diabetes Care. 2012;35(5):976-98322374636PubMedGoogle Scholar http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Archives of Internal Medicine American Medical Association

Is Sitting Harmful to Health? It Is Too Early to Say—Reply

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Publisher
American Medical Association
Copyright
Copyright © 2012 American Medical Association. All Rights Reserved.
ISSN
0003-9926
eISSN
1538-3679
DOI
10.1001/archinternmed.2012.2953
Publisher site
See Article on Publisher Site

Abstract

In reply The responses to our recent article on sitting time and mortality1 highlight the interest in, and potential importance of, sedentary behaviors and health. Our original article found that prolonged sitting was associated with increased all-cause mortality risk, independent of physical activity.1 A study limitation was the relatively short follow-up time (mean, 2.8 years), potentially leading to confounding by occult disease. However, findings persisted after adjustments (for demographic variables, physical activity, body mass index, smoking, self-rated health, and disability), chronic disease stratification, and sensitivity analyses excluding deaths in the first year. Nevertheless, neither reverse causality due to occult disease nor residual confounding could be completely excluded.1 The correspondents suggest additional potential sources of confounding and reverse causality from occupational factors including “exposure to airborne particulates and incidence of stroke; occupational stress and cardiovascular disease; occupational cancer-related mortality”; and poor diet. Although these factors might hypothetically play a role in the relationship between sitting and mortality, our study considered total sitting time and not “occupational sitting time.” Moreover, only 49% of participants in the study were in paid work. Nonoccupational sedentary behaviors (especially television viewing) have been shown to be associated with all-cause mortality,1,2 making the proposed residual confounding less likely. Furthermore, a recent similar study with an 8.5-year follow-up showed that sitting for 9 hours per day or more was associated with an all-cause mortality hazard ratio of 1.19 (95% CI, 1.12-1.27) compared with people sitting less than 3 hours per day, after extensive adjustment for confounding, including diet quality; excluding deaths in the first 3 years of follow-up suggested no evidence of reverse causality.3 Importantly, other research has suggested plausible physiological mechanisms for the detrimental effects of prolonged sitting, and findings from intervention studies indicate metabolic benefits from reductions in time spent sitting.1,4 Finally, the substantial difference between the unadjusted population attributable fraction (20.9%) calculated by Peterson and colleagues in their letter, and our adjusted population attributable fraction (6.9%)1 illustrates the importance of adjustment for confounders and suggests caution in the interpretation of unadjusted attributable risks. Our study is one piece in the accumulating evidence that prolonged sitting may be detrimental to health. It is unclear if and when this evidence will become sufficient to warrant widespread changes in policy and behavior. We agree that achieving far-reaching change is likely to be challenging, but not impossible, especially when such important health outcomes are at stake. Back to top Article Information Correspondence: Dr van der Ploeg, Department of Public and Occupational Health, VU University Medical Center Amsterdam, van der Boechorststraat 7, 1081BT Amsterdam, the Netherlands (hp.vanderploeg@vumc.nl). Financial Disclosure: None reported. Additional Contributions: Tien Chey, MAS, and Rosemary Korda, PhD, assisted with the preparation of this letter to the editor. References 1. van der Ploeg HP, Chey T, Korda RJ, Banks E, Bauman A. Sitting time and all-cause mortality risk in 222 497 Australian adults. Arch Intern Med. 2012;172(6):494-50022450936PubMedGoogle ScholarCrossref 2. Grøntved A, Hu FB. Television viewing and risk of type 2 diabetes, cardiovascular disease, and all-cause mortality: a meta-analysis. JAMA. 2011;305(23):2448-245521673296PubMedGoogle Scholar 3. Matthews CE, George SM, Moore SC, et al. Amount of time spent in sedentary behaviors and cause-specific mortality in US adults. Am J Clin Nutr. 2012;95(2):437-44522218159PubMedGoogle Scholar 4. Dunstan DW, Kingwell BA, Larsen R, et al. Breaking up prolonged sitting reduces postprandial glucose and insulin responses. Diabetes Care. 2012;35(5):976-98322374636PubMedGoogle Scholar

Journal

Archives of Internal MedicineAmerican Medical Association

Published: Sep 10, 2012

Keywords: sitting position

References