Vitamin D supplementation during first 12 months of life - Reply

摘要

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. The sun index measure is based on detailed sun exposure questions including season, time of day, duration, travel, and BSA exposed to direct sunlight, including clothing worn. The calculation of the sun index used in our study was the product of hours per week of sun exposure and percentage of BSA exposed ( x 100 as a whole number), which was adapted from child burn charts described by the World Health Organization. In adults, BSA is calculated slightly differently due to differences in the ratio of head and neck to limbs. Although calculations such as the sun index are frequently used in research studies, there is no standard, and none have been validated to quantify sun exposure in infants. Hence the discrepancy between our mean sun index values of infants at 9 months (71 [interquartile range, 42-101]; calculated as hours/week x percentage x 100 of BSA) vs those described by Barger-Lux et al3 (11.5 [interquartile range, 6.7-18.1]; calculated as hours/week x fraction of BSA) was due to differences in the units of BSA exposed (percentage of BSA as a whole number vs a fraction of BSA).