Recommended summer sunlight exposure amounts fail to produce sufficient vitamin D status in UK adults of South Asian origin

Recommended summer sunlight exposure amounts fail to produce sufficient vitamin D status in UK adults of South Asian origin1–3 Mark D Farrar, Richard Kift, Sarah J Felton, Jacqueline L Berry, Marie T Durkin, Donald Allan, Andy Vail, Ann R Webb, and Lesley E Rhodes 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. Am J Clin Nutr 2011;94:1219–24. INTRODUCTION 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). Hence, public health messages promoted by the UK Department of Health funded SunSmart campaign, and similar campaigns in other countries, recommended a limitation of summer sunlight exposure (2). National advice has also considered requirements for cutaneous vitamin D synthesis be- cause the exposure of unprotected skin to UVB in sunlight is the principal source of vitamin D, with generally small amounts obtained from the diet (3, 4). Sunlight-exposure recommendations are geared predominantly at fair-skinned individuals but in the absence of dedicated information, darker-skinned people may attempt to follow these recommendations despite having much lower risks of skin cancer. The active hormonal form of vitamin D is 1,25-dihydroxyvitamin D and is important for bone health because it is required for calcium absorption and bone mineralization (5). There is mounting evidence that vitamin D can convey other health benefits, including the potential prevention of colon cancer, diabetes, and multiple sclerosis (6–8). 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 now 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). On the basis of variables of bone health, a 25(OH)D concentration 32 ng/mL (80 nmol/L) was also proposed as optimal for health (11). 1 From Dermatological Sciences, Inflammation Sciences Research Group, School of Translational Medicine (MDF, SJF, MTD, DA, and LER) and Health Sciences Research Group, School of Community-Based Medicine (AV), University of Manchester, Manchester Academic Health Science Centre, Salford Royal National Health Service Foundation Hospital, Manchester, United Kingdom; the School of Earth, Atmospheric, and Environmental Sciences, University of Manchester, Manchester, United Kingdom (RK and ARW); and the Vitamin D Research Laboratory, Endocrine and Diabetes Research Group, School of Biomedicine, University of Manchester, Manchester Academic Health Science Centre, Manchester Royal Infirmary, Manchester, United Kingdom (JLB). 2 Supported by grants C20668/A6808 and C20668/A10007 from Cancer Research UK. 3 Address correspondence to LE Rhodes, Photobiology Unit, Dermatological Sciences, University of Manchester, Salford Royal National Health Service Foundation Hospital, Manchester, M6 8HD, United Kingdom. E-mail: . 4 Abbreviations used: MED, minimal erythemal dose; L*, lightness; PTH, parathyroid hormone; SED, standard erythemal dose; UVR, UV radiation; 25(OH)D, 25-hydroxyvitamin D. Received May 18, 2011. Accepted for publication July 29, 2011. First published online September 14, 2011; doi: 10.3945/ajcn.111.019976. Am J Clin Nutr 2011;94:1219–24. Printed in USA. Ó 2011 American Society for Nutrition 1219 1220 FARRAR ET AL There is growing evidence of vitamin D insufficiency and deficiency in the United Kingdom (12–14). Low vitamin D status is particularly prevalent in darker-skinned people, with many reports of low concentrations and related health problems in South Asians (15–20). Like many countries at a similar latitude (50–60°N), the United Kingdom has a significant and rising population of individuals of sun-reactive skin type V (ie, with brown skin) who are particularly of South Asian ethnicity (21, 22). Although South Asians reportedly have the same capacity to synthesize vitamin D as do whites (sun-reactive skin types I–IV), pigmented skin requires greater sunlight exposure to raise circulating 25(OH)D as melanin absorbs a proportion of the incident UVB (23–25). Differences in diet and lifestyle may also contribute to low vitamin D status, but the relative risks attributable to skin color are ill defined. The UK Health Protection Agency advised that vitamin D deficiency can be avoided through casual exposures to summer sunlight that contains the requisite UVB (26). On the basis of an interpretation of this advice, we showed that a course of UVR that simulated sunlight exposure over the 6-wk school summerholiday period produced 25(OH)D concentrations 20 ng/mL in 90% of the white adult population (27). To examine how skin pigmentation in South Asians influences vitamin D status outcomes, we examined the effect of the same course of UVR exposures under identical protocols in So (...truncated)