Environmental factors that influence the cutaneous production of vitamin D

Abstract

All vertebrates, including humans, obtain most of their daily vitamin D requirement from casual exposure to sunlight. During exposure to sunlight, the solar ultraviolet B photons (290-315 nm) penetrate into the skin where they cause the photolysis of 7-dehydrocholesterol to precholecalciferol. Once formed, precholecalciferol undergoes a thermally induced rearrangement of its double bonds to form cholecalciferol. An increase in skin pigmentation, aging, and the topical application of a sunscreen diminishes the cutaneous production of cholecalciferol. Latitude, season, and time of day as well as ozone pollution in the atmosphere influence the number of solar ultraviolet B photons that reach the earth's surface, and thereby, alter the cutaneous production of cholecalciferol. In Boston, exposure to sunlight during the months of November through February will not produce any significant amounts of cholecalciferol in the skin. Because windowpane glass absorbs ultraviolet B radiation, exposure of sunlight through glass windows will not result in any production of cholecalciferol. It is now recognized that vitamin D insufficiency and vitamin D deficiency are common in elderly people, especially in those who are infirm and not exposed to sunlight or who live at latitudes that do not provide them with sunlight-mediated cholecalciferol during the winter months. Vitamin D insufficiency and deficiency exacerbate osteoporosis, cause osteomalacia, and increase the risk of skeletal fractures. Vitamin D insufficiency and deficiency can be prevented by encouraging responsible exposure to sunlight and/or consumption of a multivitamin tablet that contains 10 micrograms (400 IU) vitamin D.

An estimate of premature cancer mortality in the U.S. due to inadequate doses of solar ultraviolet‐B radiation

“…The wavelength reported to be most effective in converting cholesterol to vitamin D is 295-300 nm, 50 but all the UV-B range (280 -320 nm) is reported to be effective. 51 Although there are a number of spectrally weighted UV exposure curves in the UV-B spectral region (UV-B, DNA, and erythemal [sunburning]), 52 none is exactly weighted for vitamin D production. The DNAweighted UV-B curve (centered at 300 nm with a 5-10-nm bandwidth) from the TOMS date appears to be a better approximation than the erythemally weighted curve (peaked at 300 nm but extending to 340 nm) because it is a better approximation of the vitamin D photoproduction-weighted UV-B spectrum.…”

Why the IOM recommendations for vitamin D are deficient

“…The privilege instead must be given to the intake that prevailed during the evolution of human physiology, the intake to which, presumably, that physiology is fine-tuned. So far as can be judged from numerous studies documenting the magnitude of the effect of sun exposure, (12,13) the primitive intake would have been at least 4000 IU/day and probably two to three times that level, with corresponding serum 25(OH)D levels ranging from 40 to 80 ng/mL. The fact that primitive levels would have been higher than current IOM recommendations does not, of course, prove their necessity today.…”

A phase 2 trial exploring the effects of high‐dose (10,000 IU/day) vitamin D3 in breast cancer patients with bone metastases

“…29,30 However, because exposure to sunlight can provide an adult with vitamin D in an amount equivalent to daily oral consumption of up to 10,000 IU/ day, [15][16][17][18] this dose would appear to be intuitively safe. A review of the toxicities of vitamin D has shown that except in patients with conditions causing hypersensitivity, there is no evidence of adverse effects with serum 25-hydroxyvitamin D concentrations equivalent to 10,000 IU/day.…”

“…[15][16][17][18] Furthermore, toxicities have been described at doses of 20,000 IU for 12 weeks 20 ; therefore, a 4-month duration at a dose of 10,000 IU was conservatively chosen as an optimal balance between likelihood of response and expected toxicity profile. Selfreported compliance was assessed at each follow-up visit by individual investigators.…”

“…[15][16][17][18] Furthermore, a review of data from vitamin D supplementation studies reveals a dose-response curve for vitamin D that is relatively linear up to 10,000 IU of vitamin D 3 per day, suggesting that this dose may be a physiologic upper limit. 19 The present study aimed to assess the effects of a high physiological dose of vitamin D (10,000 IU per day) on both palliation and bone turnover in women with bone metastases from breast cancer.…”