Regional differences in infant 25‐Hydroxyvitamin D: Pilot study of the Japan Environment and Children’s Study

Background 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. Methods 25‐Hydroxyvitamin D (25OHD) was measured on radioimmunoassay in 126 infants aged 2–4 years, 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. Results Both region and season during which infants participated in this study significantly affected 25OHD level (P = 0.0087 and