The role of sunlight exposure in determining the vitamin D status of the UK white Caucasian adult population.

Br J Dermatol. 2010 Aug 12.
Webb AR, Kift R, Durkin MT, O'Brien SJ, Vail A, Berry JL, Rhodes LE.
School of Earth Atmospheric and Environmental Sciences, University of Manchester, Manchester, UK.

ABSTRACT Background: Vitamin D is necessary for bone health and potentially protective against a range of malignancies. Opinions are divided on whether the proposed optimal circulating 25(OH)D level (>/= 32 ng/mL) is an appropriate and feasible target at population level. Objective: We examined whether personal sunlight exposure levels can provide vitamin D sufficient (>/= 20 ng/mL) and optimal status in the UK public.

Methods: This prospective cohort study measured circulating 25(OH)D monthly for 12 months in 125 white Caucasians aged 20-60 years in Greater Manchester. Dietary vitamin D and personal ultraviolet (UV) exposure were assessed over 1-2 weeks in each season. The primary analysis determined the post-summer peak 25(OH)D required to maintain sufficiency in winter-time.

Results: Dietary vitamin D remained low in all seasons (median 3.27 mug/day, range 2.76-4.15) while personal UV exposure levels were high in spring and summer, low in autumn and negligible in winter. Mean 25(OH)D levels were maximal in September (28.4 ng/mL; 28% optimal, zero deficient (< 5 ng/mL)), and minimal in February (18.3 ng/mL; 7% optimal, 5% deficient). A February 25(OH)D level of 20ng/mL was achieved following an average late summer level of 30.4 (25.6 to 35.2) and 34.9 (27.9 to 41.9) ng/mL in women and men, respectively, with 62% variance explained by gender and September levels.

Conclusions: Late summer 25(OH)D levels approximating the optimal range are required to retain sufficiency throughout the UK winter. Currently the majority of the population fails to reach this post-summer level and becomes vitamin D insufficient during the winter. PMID: 20716215
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