Aydin suggests that the inverse association between higher levels of vigorous physical activity and risk of advanced prostate cancer in older men may be related to solar UV exposure.1 Exposure to sun while exercising outdoors is a source of vitamin D production, and in a sample of men in our cohort, those who reported higher levels of physical activity indeed had higher circulating 25-hydroxyvitamin D concentrations. However, both nonvigorous and vigorous activities were associated with higher 25-hydroxyvitamin D concentrations, but for advanced prostate cancer, only vigorous activity was associated with lower risk. Thus, sun exposure is unlikely to be the major factor, though the general point that solar UV-B exposure may contribute to some of health benefits observed with a higher physical activity level is noteworthy.
Giovannucci E. Sun Exposure May Confound Physical Activity–Prostate Cancer Association—Reply. Arch Intern Med. 2005;165(21):2539-2540. doi:10.1001/archinte.165.21.2539