Abstract
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. 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. 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. 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. 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.
Highlights
Sunlight exposure is required for cutaneous vitamin D synthesis, but excessive exposure is the principal risk factor for the majority of skin cancers, which continue to rise in incidence in white populations [1]
The circulating concentration of 25(OH)D4 is considered the best indicator of vitamin D status, with rickets in children and osteomalacia in adults shown at 25(OH)D concentrations,5–10 ng/mL (12.5–25 nmol/L). 25(OH)D concentrations,20 ng/mL (50 nmol/L) are accepted by many authorities, including the US Institute of Medicine, to indicate vitamin D insufficiency, which is associated with bone loss, hyperparathyroidism, and muscle weakness [9, 10]
Our data showed that regular, short, midday exposures to summer sunlight at a latitude off 53.5°N while exposing ;35% of the body’s skin surface did not produce sufficient vitamin D status in individuals of South Asian ethnicity
Summary
Sunlight exposure is required for cutaneous vitamin D synthesis, but excessive exposure is the principal risk factor for the majority of skin cancers, which continue to rise in incidence in white populations [1]. 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.
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