Exposure to sunlight is a major source of vitamin D for most people. Yet public health advice has focused overwhelmingly on avoiding exposure of unprotected skin because of the risks of erythema and skin cancer. Given that there are also health risks associated with low vitamin D status, we explore the possibilities of achieving a range of targets associated with vitamin D and the accompanying erythema risk. 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 a 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. We also show that such daily, sub-erythemal doses at lunchtime during the summer months is sufficient to avoid winter-time vitamin D deficiency for the UK all-weather climate, provided that lower arms and legs are exposed in the warmer months. 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 and 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.
Keywords: 25OHD; Erythema; Exposure time; Latitude; Season; Skin area; Skin type; Sunlight exposure; Ultraviolet radiation; Vitamin D.