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Older adults are frequently cited as an at-risk population for vitamin D deficiency that may in part be due to decreased cutaneous synthesis, a potentially important source of cholecalciferol (vitamin D 3 ). Previous studies found that cutaneous D 3 production declines with age; however, most studies have been conducted ex vivo or in the photobiology lab. The purpose of this study was to characterize the response of vitamin D metabolites following a 30-min bout of sun exposure (15-min each to the dorsal and ventral sides) at close to solar noon in younger and older adults., Methods: 30 healthy individuals with skin type II/III were recruited; a younger cohort, aged 20-37 ( n = 18) and an older cohort ( n = 12), age 51-69 years. Exposure was at outer limits of sensible sun exposure designed to enhance vitamin D synthesis without increasing risk of photo ageing and non-melanoma skin cancer. Serum D 3 concentration was measured at baseline, 24, 48 and 72 h post-exposure. Serum 25(OH)D was measured at baseline and 72 h post-exposure plus 168 h post-exposure in the older cohort., Results: D 3 increased in response to sun exposure (time effect; p = 0.002) with a trend for a difference in D 3 between cohorts (time*group; p = 0.09). By regression modeling of continuous data, age accounted for 20% of the variation in D 3 production. D 3 production decreased by 13% per decade. Despite changes in D 3 , however, serum 25(OH)D did not change from baseline to 72 or 168 h post exposure ( p > 0.10)., Conclusions: Serum D 3 concentration increased significantly in response to outdoor sun exposure in younger and older adults. While ageing may dampen cutaneous synthesis, sunlight exposure is still a significant source of vitamin D 3 .