Low Vitamin D Status despite Abundant Sun Exposure

• Published in: The journal of clinical endocrinology and metabolism Vol. 92; no. 6; pp. 2130 - 2135
• Main Authors: Binkley, N, Novotny, R, Krueger, D, Kawahara, T, Daida, Y. G, Lensmeyer, G, Hollis, B. W, Drezner, M. K
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Endocrine Society 01.06.2007
• Subjects: Biological and medical sciences; Cohort Studies; Environmental Exposure; Feeding. Feeding behavior; Female; Fundamental and applied biological sciences. Psychology; Hawaii; Humans; Male; Middle Aged; Skin - metabolism; Skin - radiation effects; Sunlight; Ultraviolet Rays; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Vertebrates: endocrinology; Vitamin D - analogs & derivatives; Vitamin D - blood; Vitamin D Deficiency - diagnosis; Vitamin D Deficiency - metabolism; Metabolic diseases; Ultraviolet radiation; Nutrition; Vitamin D; Solar radiation; Endocrinology
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/jc.2006-2250

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°). 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/m2 (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.