Regional differences in infant 25-Hydroxyvitamin D: Pilot study of the Japan Environment and Children's Study.

Abstract

In recent years, a resurgence in the number of infants with vitamin D deficiency has been noted. In addition to seasonal differences in exposure to ultraviolet (UV) rays, regional differences in dietary habits and lifestyles may affect susceptibility to vitamin D deficiency. No studies have been conducted, however, on infants in multiple regions of Japan to determine the extent of differences in vitamin D status. 25-Hydroxyvitamin D (25OHD) was measured on radioimmunoassay in 126 infants aged 2-4years, who participated in the Pilot Study of the Japan Environment and Children's Study (JECS) by the Ministry of Environment of Japan. A multiple regression model with 25OHD level as the outcome variable, and season and region as explanatory variables, was generated. Both region and season during which infants participated in this study significantly affected 25OHD level (P=0.0087 and <0.0001, respectively; Wald test). Reflecting decreased exposure to UV rays, infants who were examined in winter had lower 25OHD than those examined in summer. Infants from both Fukuoka Prefecture (33°N) and Kumamoto Prefecture (32°N), however, had lower 25OHD than those from Tochigi Prefecture (36°N), contrary to expectations given the extent of UV exposure. Regional differences in daily habits and/or environmental factors affect 25OHD level in Japanese infants. The JECS is expected to identify those factors to provide guidance on preventing infantile vitamin D deficiency.