A pregnant mouse’s diet can induce changes that increase the risk her offspring will contract allergic asthma, say researchers at National Jewish Health and Duke University Medical Center. Mouse mothers on diets high in supplements containing methyl-donors, such as folic acid, birthed offspring with more severe allergic airway disease, according to a study published in the October print issue of the Journal of Clinical Investigation.

“Our findings suggest that a mother’s diet that alters DNA methylation can affect the development of the fetus’s immune system, predisposing it to allergic airway disease,” said David Schwartz, senior author on the paper and professor of medicine at National Jewish Health. “It also suggests the dramatic increase in asthma during the past two decades may be related in part to recent changes in dietary supplementation among women of childbearing age.”

Asthma, which affects about 11 percent of the U.S. population, accounts for $9.4 billion in direct healthcare costs. Although both genetics and the environment are thought to play a role in the development of asthma, scientists have been unable to identify specific causes of the disease or explain why cases of asthma have doubled in the past 25 years.

The researchers explored the role of epigenetics, the study of gene regulation, in the development of allergic asthma. Many environmental factors, from diet to smoking to medications, can modify the methyl groups that bind to DNA, especially during vulnerable periods. Although no changes are registered in the actual genetic code, epigenetic effects can be passed to offspring and can affect the development of the immune system, making it more or less likely to resist allergies.

When the researchers examined baby mice using a model of allergic asthma, they found that the mice whose mothers ate a high methyl-donor diet showed greater severity of asthma; in contrast, mice exposed to high-methyl-donor diets during lactation or adulthood showed no increased likelihood to develop allergic sensitization.

“There seems to be a crucial stage, during development in utero, when a young mouse is susceptible to epigenetic changes that can alter its immune system,” said co-author John W. Hollingsworth, assistant professor of medicine at Duke University School of Medicine. “These epigenetic changes may partially explain why it has been so difficult to definitively identify genes that contribute to asthma risk; the effect of genetic variations can be masked or further complicated by epigenetic changes.”

The current research suggests that consuming too much folic acid (and other dietary supplements) during pregnancy may lead to an increased risk of allergies and asthma, and may even play a role in the recent dramatic increase in asthma prevalence. But given the important role that folic acid supplements have played in the prevention of birth defects, the researchers do not advise any changes; instead, they write that the issue is worthy of further investigation.