Associations between outdoor light exposure and low muscle mass: An NHANES 2011 to 2014 analysis

Despite the focus of most studies on the association between ultraviolet B radiation or vitamin D and sarcopenia, the controversy still exists. The aim of this study was to explore the association between time spent outdoors (TSO) and outdoor light intensity (OLI) and the odds of sarcopenia. This study employed the National Health and Nutrition Examination Survey data in 2011 to 2014 period that included ActiGraph GT3X+ accelerometer data. Multiple logistic regression and restricted cubic spline curve were used to explore the possible association between TSO and OLI with sarcopenia. Mixed mediation analysis was used to explore possible mechanisms. Subgroup analysis and sensitivity analysis were conducted. After adjusting for all covariates, TSO and OLI were negatively associated with sarcopenia (TSO: odds ratio = 0.80 [0.68-0.94]; OLI: odds ratio = 0.78 [0.66-0.94]). A considerable part of these relationships was explained by vitamin D (9.49% for TSO; 8.44% for OLI) and testosterone (6.82% for TSO; 5.14% for OLI). The chain mediation path of "vitamin D → testosterone" mediated 1% of the association between the 2 variables, TSO and OLI, with sarcopenia. TSO and OLI were negatively associated with sarcopenia. Vitamin D and testosterone, parallel and chain, mediated this negative association.