When measuring sun exposure at the individual level, many scientists have relied on latitude or ambient UVR of residence. But these measures are fraught with uncertainties. “While ambient UVR varies, . . . so too do a variety of other possible etiological factors, including diet, exposure to infectious agents, temperature, and possibly even physical activity levels,” says Robyn Lucas, an epidemiologist at Australia’s National Centre for Epidemiology and Population Health. “Additionally, under any level of ambient UVR, the personal UV dose may vary greatly. In short, there is no real specificity for ambient UVR.” Researchers also assess history of time in the sun at various ages, history of sunburns, dietary and supplemental vitamin D intake, and other proxy measures. Nonetheless, says Lucas, “there are drawbacks to inferring that a relationship with any proxy for the exposure of interest is a relationship with personal UV dose or vitamin D status.” On the bright side, she adds, our ability to accurately gauge an individual’s UV dose history has been enhanced with the use of silicone rubber casts of the back of subjects’ hands. The fine lines recorded by the cast provide an objective measure of cumulative sun damage. - www.ncbi.nlm.nih.gov