Estimating personal solar ultraviolet radiation exposure through time spent outdoors, ambient levels and modelling approaches.

BACKGROUND  Evidence on validation of surrogates applied to evaluate the personal exposure levels of solar ultraviolet radiation (UVR) in epidemiological studies is scarce. OBJECTIVES  To determine and compare the validity of three approaches, including (i) ambient UVR levels, (ii) time spent outdoors, and (iii) a modelling approach integrating the aforementioned parameters, to estimate personal UVR exposure over a period of six months among indoor and outdoor workers and in different seasons (summer/winter). METHODS  This validation study was part of the EU ICEPURE project and was performed between July 2010 and January 2011 in a convenience sample of indoor and outdoor workers in Catalunya - Spain. We developed linear regression models to quantify the variation in the objectively measured personal UVR exposure that could be explained, separately, by the ambient UVR, time spent outdoors, and modelled UVR levels. RESULTS Our 39 participants - mostly male and with a median age of 35 years- presented a median daily objectively measured UVR of 0.37 standard erythemal doses (SEDs). The UVR dose was statistically significantly higher in summer and for outdoor workers. The modelled personal UVR exposure and self-reported time spent outdoors could reasonably predict the variation in the objectively measured personal UVR levels (R2 = (0.75, 0.79)), whereas ambient UVR was a poor predictor (R2 =0.21). No notable differences were found between seasons or occupation. CONCLUSIONS  Time outdoors and our modelling approach were reliable predictors and of value to be applied in epidemiological studies of the health effects of current exposure to UVR.