Sun exposure questionnaire predicts circulating 25-hydroxyvitamin D concentrations in Caucasian hospital workers in southern Italy

Recent sun exposure should correlate with circulating 25-hydroxyvitamin D [25(OH)D] due to ultraviolet B (UVB)-catalyzed cutaneous synthesis of vitamin D. A Sun Exposure Score was calculated for healthy adults using a recall questionnaire assessing daily Time in Sun (30 min) and Skin Exposure (face/hands; face/hands and arms; face/hands and legs; and “bathing suit”) for 1 week in each of the winter and summer ( n = 47 and 23, respectively; n = 18 participated in both). Concentrations of 25(OH)D were measured by DiaSorin RIA on end-of-week sera. Mean serum 25(OH)D was higher in summer than winter (58.6 ± 16.5 nmol/L vs. 38.8 ± 29.0 nmol/L, respectively, P = 0.003 unpaired). The calculated Sun Exposure Score correlated strongly with serum 25(OH)D during summer (Spearman's rho = 0.59, P = 0.003); based on the Pearson coefficient of determination, summer Sun Exposure Score explained 38% of the variability in summer serum 25(OH)D. The Sun Exposure Score did not correlate with 25(OH)D in the winter (rho = 0.19, P = 0.210). The summer correlation was largely explained by the Time in Sun (rho = 0.58, P = 0.004) rather than area of Skin Exposed (rho = 0.10, P = 0.660). Although there was a correlation between winter and summer Sun Exposure Scores (rho = 0.63, P = 0.005), there was no summer vs. winter correlation in serum 25(OH)D (rho = 0.08, P = 0.76). This simple 1-week sun exposure recall questionnaire predicted summer serum 25(OH)D concentrations, accounting for 38% of the variability in 25(OH)D among healthy Italian adults.