Joh HK, et al. - Because vitamin D inadequacy is associated with a wide range of diseases, researchers investigated the impact of sun exposure vs oral vitamin D supplementation on serum 25-hydroxyvitamin D levels in young adults in this 8-week randomized, placebo-controlled clinical trial. Specifically, they compared vitamin D-deficient adults in Seoul, Korea, with respect to changes in serum 25OHD concentrations. Participants were assigned to sun exposure (daily ≥ 20–30 minutes around noon; n=50), oral vitamin D₃ (500 IU/d; n=50), and control (placebo; n=50) groups. They found that sun exposure and oral vitamin D₃ increased serum 25OHD concentrations effectively. They observed that enhanced sun exposure and 500 IU/d of oral vitamin D₃ supplementation increased serum 25OHD concentrations significantly. However, the sun exposure protocol was not as effective as supplementation with oral vitamin D₃ at 500 IU/d. Changes in cardiometabolic markers in all groups were mostly insignificant.