Effects of physical activity on melatonin levels in previously sedentary men and women.

BACKGROUND: The inverse association between physical activity and cancer risk may be mediated by higher melatonin levels. However, few studies have examined the effect of increased physical activity on melatonin levels.
METHODS: The parent study was a randomized controlled trial that randomized 51 men and 49 women to a 12-month moderate-to-vigorous aerobic exercise intervention ("exercisers") and 51 men and 51 women to a stretching control ("controls"). Participants were of ages 40 to 75 years, and previously sedentary. Levels of the principal urinary metabolite of melatonin, 6-sulfatoxymelatonin (aMT6s), corrected for creatinine levels, were measured in spot morning urine samples by immunoassay at baseline and 12 months. Changes in levels between exercisers and controls were compared using generalized estimating equations for linear regression.
RESULTS: We observed no statistically significant difference in the change in aMT6s levels from baseline to 12 months in exercisers compared with controls (change in aMT6s levels: exercisers, +6.5%; controls, +13%; P = 0.66). There was no evidence of effect modification by age, sex, or body mass index.
CONCLUSIONS: A 12-month moderate-intensity exercise intervention did not affect levels of aMT6s. IMPACT: Further research needs to focus on other potential mechanisms through which physical activity may reduce the risk of cancer. Cancer Epidemiol Biomarkers Prev; 23(8); 1696-9. ©2014 AACR. ©2014 American Association for Cancer Research.

RCT Entities:   Population Interventions Outcomes