In Reply Drs Sofiyan and Nanan highlight an important issue within the vitamin D research field. The estimation of sunlight exposure is often imprecise due to recall bias and is particularly challenging among children with sporadic patterns of exposure. We chose to estimate UV exposure using the sun index. Although more objective measures of UV exposure are available, such as dosimeters, they do not incorporate capacity for cutaneous vitamin D synthesis on the basis of body surface area (BSA) exposed.
Gallo S, Rodd C, Weiler H. Vitamin D Supplementation During First 12 Months of Life—Reply. JAMA. 2013;310(8):853-854. doi:10.1001/jama.2013.124272