Abstract
Abstract— An attempt has been made to calculate the rate of ultraviolet absorption by 7‐dehydrocholes‐terol. provitamin D3, in the epidermis as a function of latitude, season and skin type, in the hope that it will provide an upper‐limit estimate of the epidermal vitamin production. The results indicate that a significant fraction of the total epidermal production may occur in the stratum corneum with figures of 15 and 31% being found for non‐pigmented and pigmented epidermises, respectively. Total production in negroid epidermis is predicted to be about 40% of that in the Caucasian one and the latitudinal variation is greater than the seasonal variation, in agreement with the behaviour of the available solar ultraviolet. Overall production rates are sufficiently high for it to be unnecessary to invoke an enhanced absorption mechanism for the provitamin, although the results do indicate that there may be a risk of deficient production above about 40oN.
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