Validation of brief questionnaire measures of sun exposure and skin pigmentation against detailed and objective measures including vitamin D status

Self-reported sun exposure is commonly used in research, but how well this represents actual sun exposure is poorly understood. From February to July 2011, a volunteer sample (n = 47) of older adults (≥45 years) in Canberra, Australia, answered brief questions on time outdoors (weekdays and weekends) and natural skin color. They subsequently maintained a sun diary and wore an ultraviolet radiation (UVR) digital dosimeter for 7 days. Melanin density was estimated using reflectance spectrophotometry; lifetime sun damage was assessed using silicone casts of the back of the hand; and serum 25-hydroxyvitamin D (25(OH)D) concentration was assayed. Questionnaire-reported time outdoors correlated significantly with diary-recorded time outdoors (Spearman correlation r_s = 0.66; 95% CI 0.46, 0.80; P < 0.001) and UVR dosimeter dose (r_s= 0.46; 95% CI 0.18, 0.68; P = 0.003), but not 25(OH)D concentration (r_s = 0.24; 95% CI -0.05, 0.50; P = 0.10). Questionnaire-reported untanned skin color correlated significantly with measured melanin density at the inner upper arm (r_s = 0.49; 95% CI 0.24, 0.68; P < 0.001). In a multiple linear regression model, statistically significant predictors of 25(OH)D concentration were self-reported frequency of physical activity, skin color and recent osteoporosis treatment (R² = 0.54). In this study, brief questionnaire items provided valid rankings of sun exposure and skin color, and enabled the development of a predictive model for 25(OH)D concentration. We examined the validity of a brief questionnaire measure of usual "time outdoors" on weekdays and weekends. This measure was compared to both time outdoors recorded in a 7-day sun exposure diary, and objectively measured (electronic dosimeter) UVR exposure. This figure shows the association between questionnaire and diary measures of average weekly time outdoors; the two were significantly and moderately correlated. We further report a significant correlation between questionnaire "time outdoors" and objectively measured UVR exposure. Therefore, our results indicate that the brief questionnaire measure of usual time outdoors can be used to rank respondents according to current sun exposure.