Invited Commentary: Physical Activity and Vitamin D

Abstract

Exercise and vitamin D are both important for musculoskeletal health. In this issue of the Journal, Scragg and Camargo (Am J Epidemiol 2008;168:577–86) provide a new analysis of relatively old data on physical activity and vitamin D from the Third National Health and Nutrition Examination Survey (1988–1994). This commentary considers the methodological strengths and weaknesses of the study and concludes that the findings are as robust as could reasonably be expected from a cross-sectional design. Consideration is given to whether outdoor exercise is the cause of higher vitamin D levels and, if so, whether mortality gains may accrue from more widespread participation. A note of caution is sounded, given the disappointing results on studies of the prevention of falls and fractures with vitamin D supplementation in community-dwelling populations. However, this is an important observation, and more epidemiologic studies are needed, preferably including care home residents. Applied researchers should consider further studies of vitamin D supplementation in older people, possibly combined with an exercise intervention. Public health professionals and practicing clinicians should recognize that there is a rationale for recommending outdoor exercise, and they should seek to improve universal accessibility.