A woman’s overall diet during pregnancy may not be related to her child’s risk of developing wheezing problems by preschool age, a new study suggests.

Wheezing refers to a high-pitched whistling sound, most obvious while exhaling, that is usually caused by blockages in the small breathing tubes in the chest.

Occasional wheezing is common in infancy and early childhood, and is often related to viral infections. But young children with recurrent wheezing episodes are more likely than other children to develop asthma, particularly if they have risk factors such as family history of allergies and asthma.

Several studies have found connections between a pregnant woman’s intake of specific foods or nutrients and her child’s risk of developing recurrent wheezing or asthma.

Women who eat more fish, apples, omega-3 fatty acids and vitamins D and E, for example, seem to have relatively lower risks of the breathing problems. However, those studies do not prove that the foods and nutrients themselves bring the benefit.

One of the questions has been whether women who consume more of those foods simply have a healthier diet overall, and it’s the overall diet pattern that matters.

So for the new study, reported in the Journal of Allergy and Clinical Immunology, researchers looked at the relationship between diet patterns during pregnancy and wheezing risk among 1,376 mother-child pairs. Mothers completed detailed dietary questionnaires during their first and second trimesters, and their children’s rates of recurrent wheezing were followed to the age of 3.

Overall, 18 percent of the children developed repeat bouts of wheezing, based on parents’ questionnaire responses.

In general, the researchers found no differences in the children’s risk of wheezing, whether their mothers’ diet during pregnancy fit a generally healthful pattern or less-than-optimal one.

Healthy patterns included a “Mediterranean”-style diet - typically high in fish, fruits and vegetables, olive oil, nuts and whole grains - and a “prudent” diet, rich in fruits and vegetables, whole grains, fish, poultry and eggs.

The less-than-healthful diet - called the “Western” pattern - included relatively high amounts of red and processed meats, high-fat dairy, sweets and refined grains like white bread.

The researchers stress, however, that the lack of a link between these eating patterns and wheezing risk does not diminish the importance of a healthy diet during pregnancy.

“For many reasons, both for the mother and child, it is important for mothers to eat a healthy diet,” said lead researcher Dr. Nancy M. Lange, of Brigham and Women’s Hospital and Harvard Medical School in Boston.

Nor do the current findings mean that nutrition during pregnancy has no role in the risk of childhood asthma, according to Lange.

Instead, she told Reuters Health in an email, they suggest that future studies should continue to investigate the links between specific nutrients during pregnancy and children’s wheezing and asthma risk.

For now, Lange said, no recommendations on specific foods or nutrients can be made.

She explained that the existing evidence linking benefits to certain vitamins and foods come from observational studies - where researchers asked women about their nutrition during pregnancy, then looked at the rates of wheezing or asthma among their children.

Such studies cannot prove cause-and-effect.

“It would be premature to recommend that women with a history of asthma, or without this history, take anything specific for the purposes of preventing asthma in their children,” Lange said.

Clinical trials to confirm any benefit of specific nutrients have yet to be done, she noted.

They are, however, in the works. One ongoing trial, for example, is testing whether giving pregnant women extra vitamin D has any effect on their children’s risk of recurrent wheezing by the age of 3.

SOURCE: Journal of Allergy and Clinical Immunology, online June 28, 2010.