SPENDING more time outdoors may be associated with healthier testosterone levels in adult men, according to new cross-sectional research using data from the US National Health and Nutrition Examination Survey (NHANES). While physical activity and vitamin D have been studied extensively in relation to testosterone, time spent outdoors (TSO) itself has received comparatively little attention. Time Outdoors and Its Impact on Testosterone in Adult MenAfter adjustment for confounding factors, greater TSO was significantly associated with higher serum testosterone levels. Consistent with previous research, increasing age, higher BMI, and the presence of diabetes were all positively associated with low testosterone, while higher levels of physical activity were inversely associated. Cross-sectional association of time spent outdoors with serum testosterone: results from the national health and nutrition examination survey.