NO SURE THING: Asthma and asthma symptoms did occur in some children whose… (Gary Friedman / Los Angeles…)
What's new: A pregnant woman who eats nuts or nut products every day during pregnancy may increase her child's risk of developing asthma.
The finding: A large study by the Dutch government has found that children born to women who ate nuts or peanuts, or items made from them, such as peanut butter, daily while pregnant were 50% more likely to wheeze, have difficulty breathing or have asthma diagnosed by a doctor compared with children whose mothers rarely or never ate nuts or nut products while pregnant. The study, published in the American Journal of Respiratory and Critical Care Medicine this month, is part of a larger, ongoing research initiative, the Prevention and Incidence of Asthma and Mite Allergy study, which is investigating how allergies develop in children and how they can be prevented.
Another finding: The odds of developing one particular asthma symptom -- wheezing --were reduced in children whose mothers ate fruit daily during pregnancy, but the design of the study made it difficult for the researchers to conclusively link the two in a cause-effect relationship.
How the study was done: Nearly 4,000 expectant mothers, recruited into the study more than a decade ago, completed a dietary questionnaire on how often they ate fish, eggs, milk and milk products, nuts and nut products, fresh fruit and vegetables. Researchers followed up on the women's offspring at 3 months old and then once a year until the children were 8, gathering information about the children's diets, allergies and asthma symptoms.
Aside from nuts, none of the other dietary components appeared to affect the children's likelihood of developing asthma or asthma-related symptoms. The food the children ate also appeared to have no bearing on their risk of asthma. Only the children whose mothers ate nuts or nut products every day while pregnant were more likely to experience wheezing, shortness of breath or other asthma symptoms.
Why it matters: A scientifically validated link between what a woman eats and her child's risk of a health problem would, of course, affect the advice doctors give to expectant mothers -- and, it is hoped, reduce the incidence of that problem.
Numerous studies have tried to clarify the relationship between a woman's diet during pregnancy and the development of asthma or allergies in her child. Researchers have found that some vitamins and minerals (such as vitamin D and iron), as well as some foods (such as fish and apples), may protect against asthma and allergies. Others have shown that exposure to peanuts while in utero may increase a child's risk of developing an allergy to them. But the current study, its authors say, is the first of its kind to follow up with its participants repeatedly over a long period, and thus is expected to be more reliable.
This study is also significant for what it didn't show. Unlike those earlier studies that found that eating more fish during pregnancy can reduce the risk of asthma or allergies in offspring, the Dutch researchers produced no evidence to support those findings. (They were unable to draw conclusions about apples or specific vitamins or minerals, however, because they didn't ask mothers for such dietary details.)
What we still don't know: How could fetal exposure to nuts trigger asthma? Scientists have proposed a number of ideas, but the precise mechanisms are still unknown. Though the study suggests a link between nut consumption and asthma, it doesn't show that a woman who avoids nuts during pregnancy has found a surefire way to prevent asthma in her offspring: Asthma and asthma symptoms did occur in some children whose mothers rarely or never ate nuts while pregnant. The study may be large and well designed, but its findings will need to be replicated before its results can join the legions of advice given to pregnant women across the globe.
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