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Clinical Trial
. 2011 Nov;94(5):1219-24.
doi: 10.3945/ajcn.111.019976. Epub 2011 Sep 14.

Recommended Summer Sunlight Exposure Amounts Fail to Produce Sufficient Vitamin D Status in UK Adults of South Asian Origin

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Clinical Trial

Recommended Summer Sunlight Exposure Amounts Fail to Produce Sufficient Vitamin D Status in UK Adults of South Asian Origin

Mark D Farrar et al. Am J Clin Nutr. .

Abstract

Background: The cutaneous synthesis of vitamin D is dependent on UVB from sunlight, but melanin reduces the penetration of UVB and thus contributes to vitamin D insufficiency in individuals with darker skin. The national guidance provided on amounts of sunlight exposure in the United Kingdom is for the light-skinned population, and in the absence of dedicated information, darker-skinned people may attempt to follow this guidance.

Objectives: We determined the relative effect of a simulation of UK recommendations of summer sunlight exposure on the vitamin D status of individuals of South Asian ethnicity compared with that of whites.

Design: In a prospective cohort study, simulated summer sunlight exposures were provided under rigorous dosimetric conditions to 15 adults (aged 20-60 y) of South Asian ethnicity, and serum 25-hydroxyvitamin D [25(OH)D] was measured weekly. Dietary vitamin D intake was estimated. Outcomes were compared with those of 109 whites (aged 20-60 y) treated with the identical UV-radiation exposure protocol.

Results: At baseline (winter trough), all South Asians were vitamin D-insufficient [25(OH)D concentrations <20 ng/mL], and 27% of South Asians were vitamin D-deficient [25(OH)D concentrations <5 ng/mL]; although 25(OH)D concentrations increased postcourse (P < 0.0001), all South Asians remained vitamin D-insufficient. The mean increase in 25(OH)D was 4.3 compared with 10.5 ng/mL in the South Asian and white groups, respectively (P < 0.0001), and 90% of the white group reached vitamin D sufficiency postcourse. The median dietary vitamin D intake was very low in both groups.

Conclusions: Sunlight-exposure recommendations are inappropriate for individuals of South Asian ethnicity who live at the UK latitude. More guidance is required to meet the vitamin D requirements of this sector of the population. This study was registered at www.isrctn.org as ISRCTN 07565297.

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