Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes

Background: The relationship between oral vitamin D supplementation and cutaneous photosynthesis is not well understood. Objective: We sought to provide estimates of the equivalency of vitamin D production from natural sun exposure versus oral supplementation. Methods: Using the FastRT simulation tool, we determined sun exposure times needed to achieve serum vitamin D-3 concentrations equivalent to 400 or 1000 IU vitamin D for individuals of various Fitzpatrick skin types living in Miami, FL, and Boston, MA, during the months of January, April, July, and October. Results: Peak ultraviolet B irradiation for vitamin D synthesis occurs around 12 PM Eastern Standard Time (EST). In Boston, MA, from April to October at 12 pm EST an individual with type III skin, with 25.5% of the body surface area exposed, would need to spend 3 to 8 minutes in the sun to synthesize 400 IU of vitamin D. Ills difficult to synthesize vitamin D during the winter in Boston, MA. For all study months in Miami, FL, an individual with type III skin would need to spend 3 to 6 minutes at 12 PM EST to synthesize 400 IU. Vitamin D synthesis occurs faster in individuals with lighter Fitzpatrick skin types. The duration to attain 1000 IU of vitamin D is longer in all scenarios. Limitations: Results of the computer model are only approximations. In addition, calculations were made based on the assumption that (1)/(4) of 1 minimal erythema close directed at (1)/(4) body surface area is equal to 1000 IU of oral vitamin D. Conclusions: Although it may be tempting to recommend intentional sun exposure based on our findings, it is difficult, if not impossible to titrate one's exposure. There are well-known detrimental side effects of ultraviolet irradiation. Therefore, oral supplementation remains the safest way for increasing vitamin D status. (J Am Acad Dermatol 2010;62:929-34.)