The Contributions of Solar Ultraviolet Radiation Exposure and Other Determinants to Serum 25-Hydroxyvitamin D Concentrations in Australian Adults: The AusD Study

The Quantitative Assessment of Solar UV [ultraviolet] Exposure for Vitamin D Synthesis in Australian Adults (AusD) Study aimed to better define the relationship between sun exposure and serum 25-hydroxyvitamin D (25(OH)D) concentration. Cross-sectional data were collected between May 2009 and December 2010 from 1,002 participants aged 1875 years in 4 Australian sites spanning 24 of latitude. Participants completed the following: 1) questionnaires on sun exposure, dietary vitamin D intake, and vitamin D supplementation; 2) 10 days of personal ultraviolet radiation dosimetry; 3) a sun exposure and physical activity diary; and 4) clinical measurements and blood collection for 25(OH)D determination. Our multiple regression model described 40 of the variance in 25(OH)D concentration; modifiable behavioral factors contributed 52 of the explained variance, and environmental and demographic or constitutional variables contributed 38 and 10, respectively. The amount of skin exposed was the single strongest contributor to the explained variance (27), followed by location (20), season (17), personal ultraviolet radiation exposure (8), vitamin D supplementation (7), body mass index (weight (kg)/height (m)(2)) (4), and physical activity (4). Modifiable behavioral factors strongly influence serum 25(OH)D concentrations in Australian adults. In addition, latitude was a strong determinant of the relative contribution of different behavioral factors.