Prenatal vitamin D protects from asthma

High levels of vitamin D during pregnancy may lower the risk of wheezing and asthma in offspring during early childhood. While vitamin D has important effects on the immune system, its affect on asthma is not known. Researchers from the Harvard Medical School in Boston, USA, tracked 1,306 mother-child pairs for more than three years, and used a food frequency questionnaire to assess levels of maternal vitamin D during pregnancy. By age two, there was a clear association between increasing prenatal levels of vitamin D in the mother and decreasing risk of wheezing or doctor-diagnosed asthma in the child. The average total vitamin D intake during pregnancy was 550 international units (IU) per day. In a more thorough analysis, a 100-IU increase in maternal vitamin D intake was associated with an odds ratio of 0.90 for any wheeze in the child, defined as mother-reported wheeze, during the first two years of life. When the data were adjusted to account for dietary levels of fruit, vegetables, and fish, the results did not change. This inverse association was present for vitamin D from either diet or nutritional supplements. They also reported that a preliminary look at the three-year data show a similar strong association between higher maternal vitamin D levels and lower risk of wheezing and asthma at age three years. However, follow-up is needed to see if the lower risk of wheezing continues, as the children grow older.