Vitamin DFactors that influence the cutaneous synthesis and dietary sources of vitamin D
Section snippets
Human study
Healthy adults with different skin types (II, III, IV and V) were recruited in the beginning of winter to participate in our study. They were asked to lie in a tanning bed (source of UV irradiation) to expose whole body to a light similar to sunlight. Based on the manufacturer recommendation each volunteer received a total of 0.75 of MED (minimal erythema dose) in each session. To achieve that goal, the skin type II, III, IV and V received an average of 6, 8, 11, and 12 min of UV irradiation
Results
To investigate the effect of skin pigmentation on previtamin D3 synthesis in humans, we exposed type II and type V skin along with ampoules containing 7-DHC solution to noon sunlight in June on a cloudless day in Boston, Massachusetts. We found that in June, 0.67 ± 0.11% of 7-DHC in epidermis was converted to previtamin D3 in type II skin, but no detectable amount was found in type V skin samples after 5 min of sunlight exposure (Fig. 1). A small amount (0.18 ± 0.06%) of epidermal 7-DHC was
Discussion
Vitamin D3 is unique among numerous vitamins and hormones in that it is derived from a precursor, previtamin D3, which is synthesized in the skin in response to solar irradiation [14]. The photoproduction of previtamin D3 is dependent on the concentration of 7-DHC in epidermis and melanin pigmentation [23], [24]. There is an inverse relation between the concentrations of provitamin D3 in the epidermis with age [23]. The percentage conversion of cutaneous 7-DHC is also influenced by the solar
Acknowledgments
This work was supported in part by Grants (RO1AR-36963-05, R37AG6079-07, and MO1RR00053) from the National Institutes of Health, and a grant from the UV Foundation.
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Present address: Nephrology Division, Department of Medicine, Harvard Medical School, Boston MA 02215, USA.