Ultraviolet exposure scenarios: risks of erythema from recommendations on cutaneous vitamin D synthesis.

Exposure to sunlight is a major source of vitamin D for most people yet public health advice focuses overwhelmingly on avoiding exposure of unprotected skin because of the risks of erythema and skin cancer. We have calculated the exposure required to gain a number of proposed oral-equivalent doses of vitamin D, as functions of latitude, season, skin type and skin area exposed, together with the associated risk of erythema, expressed in minimum erythema doses. The model results show that the current recommended daily intake of 400 IU is readily achievable through casual sun exposure in the midday lunch hour, with no risk of erythema, for all latitudes some of the year and for all the year at some (low) latitudes. At the higher proposed vitamin D dose of 1000 IU lunchtime sun exposure is still a viable route to the vitamin, but requires the commitment to expose greater areas of skin, or is effective for a shorter period of the year. The highest vitamin D requirement considered was 4000 IU per day. For much of the globe and much of the year, this is not achievable in a lunchtime hour and where it is possible large areas of skin must be exposed to prevent erythema. When the only variable considered was skin type, latitudinal and seasonal limits on adequate vitamin D production were more restrictive for skin type 5 than skin type 2.