Background: Adequate vitamin D status in mothers during pregnancy may influence the health status of the child later in life. We assessed whether maternal circulating 25-hydroxyvitamin D (25[OH]D) concentrations in pregnancy are associated with risk of lower respiratory tract infections, wheezing, and asthma in the offspring. Methods: Data were obtained from 1724 children of the INfancia y Medio Ambiente (INMA) Project, a population-based birth cohort study. Maternal circulating 25(OH)D concentrations were measured in pregnancy (mean gestational age = 12.6 [SD = 2.5] weeks). When the child was age 1 year, parents were asked if their child had a physician-confirmed history of lower respiratory tract infections or a history of wheezing. The questions about wheezing were repeated annually thereafter. Asthma was defined as parental report of doctor diagnosis of asthma or receiving treatment at the age of 4-6 years or wheezing since the age of 4 years. Results: The median maternal circulating 25(OH)D concentration in pregnancy was 29.5 ng/mL (interquartile range, 22.5-37.1 ng/mL). After multivariable adjustment, there was a trend for an independent association between higher levels of maternal circulating 25(OH)D levels in pregnancy and decreased odds of lower respiratory tract infections in offspring (for cohort-and season-specific quartile Q4 vs. Q1, odds ratio = 0.67 [95% confidence interval = 0.50-0.90]; test for trend, P = 0.016). We found no association between 25(OH)D levels in pregnancy and risk of wheezing at age 1 year or 4 years, or asthma at age 4-6 years. Conclusions: Higher maternal circulating 25(OH)D concentrations in pregnancy were independently associated with lower risk of lower respiratory tract infections in offspring in the first year of life but not with wheezing or asthma in childhood.
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