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. 2007 Jun;92(6):2130-5.
doi: 10.1210/jc.2006-2250. Epub 2007 Apr 10.

Low vitamin D status despite abundant sun exposure

N Binkley  1 , R Novotny, D Krueger, T Kawahara, Y G Daida, G Lensmeyer, B W Hollis, M K Drezner
Affiliations

Low vitamin D status despite abundant sun exposure

N Binkley et al. J Clin Endocrinol Metab. 2007 Jun.

Abstract

Context: Lack of sun exposure is widely accepted as the primary cause of epidemic low vitamin D status worldwide. However, some individuals with seemingly adequate UV exposure have been reported to have low serum 25-hydroxyvitamin D [25(OH)D] concentration, results that might have been confounded by imprecision of the assays used.

Objective: The aim was to document the 25(OH)D status of healthy individuals with habitually high sun exposure.

Setting: This study was conducted in a convenience sample of adults in Honolulu, Hawaii (latitude 21 degrees ).

Participants: The study population consisted of 93 adults (30 women and 63 men) with a mean (sem) age and body mass index of 24.0 yr (0.7) and 23.6 kg/m(2) (0.4), respectively. Their self-reported sun exposure was 28.9 (1.5) h/wk, yielding a calculated sun exposure index of 11.1 (0.7).

Main outcome measures: Serum 25(OH)D concentration was measured using a precise HPLC assay. Low vitamin D status was defined as a circulating 25(OH)D concentration less than 30 ng/ml.

Results: Mean serum 25(OH)D concentration was 31.6 ng/ml. Using a cutpoint of 30 ng/ml, 51% of this population had low vitamin D status. The highest 25(OH)D concentration was 62 ng/ml.

Conclusions: These data suggest that variable responsiveness to UVB radiation is evident among individuals, causing some to have low vitamin D status despite abundant sun exposure. In addition, because the maximal 25(OH)D concentration produced by natural UV exposure appears to be approximately 60 ng/ml, it seems prudent to use this value as an upper limit when prescribing vitamin D supplementation.

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