As if mothers-to-be don't have enough to worry about, new research suggests that eating certain foods during pregnancy or while breast-feeding may raise the baby's risk of allergies and asthma later in life.

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By Denise Mann

SUNDAY, Feb. 28, 2010 ( — As if mothers-to-be don't have enough to worry about, new research suggests that eating certain foods during pregnancy or while breast-feeding may raise the baby's risk of allergies and asthma later in life.

The good news is that if women—particularly those in allergy-prone families—avoid nuts, eggs, and milk during and after pregnancy, they may lower their child's risk of developing food allergies or asthma, according to a study presented at the annual meeting of the American Academy of Allergy, Asthma & Immunology in New Orleans.

Expectant women who consume little folic acid—a type of B vitamin recommended during pregnancy to prevent birth defects—may also be less likely than women who consume more to have children with asthma, according to a second study, also presented at the meeting.

The studies come at a time when food allergies are on the rise among kids in the United States. Between 1997 and 2007, the percentage of children under age 18 with food allergies increased by 18%, according to the U.S. Centers for Disease Control and Prevention. Children who have food allergies have been shown to be at higher risk for developing asthma and other allergic diseases (like eczema).

The first study looked at 274 pregnant women in Australia who already had a child with food allergies. Researchers told the moms that they should avoid nuts, eggs, and milk during the third trimester of their pregnancies, while breast-feeding, and at least until their baby's first birthday.

After the children were born, researchers tested them for food allergies and asthma at age 18 months and at 3 years. At the three-year mark, just 16% of the children whose mothers followed the dietary advice tested positive for peanut allergy, compared to 52% of the children whose mothers didn't follow the advice. The rates of egg allergy were also substantially lower in the women who avoided nuts, eggs, and milk.

What's more, 11% of the 3-year-olds whose mothers avoided the foods had developed symptoms of asthma. In the other group, the rate was 43%.

The children whose mothers followed the advice also had lower rates of dust-mite allergies and eczema at 18 months, although these differences were no longer measurable three years out.

Andrew Liu, MD, an associate professor of pediatrics at National Jewish Health, in Denver, calls the findings "intriguing."

"It's logical," says Dr. Liu. "This would not benefit every child, but if you already have a food-allergic child in the family, this could be helpful. This kind of avoidance may help kids who are already at high risk for food allergies and asthma, even before they're born."

However, the study's lead author, Velencia Soutter, MBBS, a pediatrician at the Royal Prince Alfred Hospital, in Sydney, says that the diet advice used in the study can be difficult to stick to. "While it's probably too hard for most people, parents who already have a child with an allergy have the choice to reduce the risk of particular food allergies in their next child," she says.

In the second study, researchers in Norway measured the folate levels of about 2,000 pregnant women during their second trimester. Compared to the children of the moms with the lowest levels, the children of the women with the highest folate levels were more likely to have symptoms of asthma at age 3.

Folate is the naturally occurring form of folic acid, a B vitamin. Because folic acid is believed to reduce the risk of brain- and spinal-related birth defects, most experts recommend that pregnant women take prenatal vitamins with 400 micrograms of folic acid every day before pregnancy and during early pregnancy.

In the United States, folate is also found in green, leafy vegetables and fortified foods such as breads, cereals, and other grain products. In Norway, however, the food supply is not fortified with folic acid.

"We may be overdoing folic acid," says Ivana Yang, PhD, an assistant professor of genetics at National Jewish Health. (Yang was not involved in the new study.)

"The dose that was picked for pregnant woman to avoid neural tube defects was arbitrary," she says. "If it has to be this high to prevent neural tube defects, then asthma is something we have to deal with. But all of our food is also fortified with folic acid, so we're taking crazy amounts if we add it all up."

Experts aren't exactly sure how too much folic acid during pregnancy could lead children to develop asthma. "It may be that it modifies your genetic material, which may decrease expression of certain genes and set the stage for the development of asthma," Yang explains.

More research is needed before the folic acid recommendations are changed, she adds.