Nov. 1, 2007 -- Prolonged breastfeeding appears to promote healthy lung development in most children, but it may increase the risk of asthma in babies born to mothers with the respiratory disease, new research suggests.
Being breastfed for four months or longer was associated with worse lung function among children with asthmatic mothers, compared to children breastfed for shorter periods whose mothers also had asthma.
The findings suggest that long-term breastfeeding may not be the best strategy for asthmatic mothers, but it is premature to suggest a change in breastfeeding recommendations, says researcher Theresa W. Guilbert, MD.
Guilbert tells WebMD that the study findings must first be confirmed.
"As a pediatrician and a mother of three who breastfed, I want to emphasize that breast is best," she says. "We know that breastfeeding is good for brain development and that breastfed babies have less ear infections. And there are many other benefits. But there may be an aspect to breastfeeding that isn't totally positive."
Asthma and Breastfeeding
Guilbert and colleagues analyzed data from the ongoing Children's Respiratory Study in Tucson, Ariz. -- one of the longest "follow" studies examining asthma and allergies in children ever conducted.
Their research involved 679 study participants followed from birth through their teens, whose lung function was tested at age 11 and again at age 16. Lung function testing is used to assess asthma.
The researchers found that children born to mothers without asthma or those who were predisposed to develop allergies had improved lung function when they had been breastfed for four months or longer.
But the opposite was true for children with mothers who had asthma.
Compared to children of asthmatic mothers breastfed for shorter periods, those breastfed for four months or longer had a 6% reduction in certain lung function testing at 16 years.
"That represents a pretty significant reduction," asthma expert Homer A. Boushey, Jr., MD, tells WebMD.
The study appears in the November issue of the American Journal of Respiratory and Critical Care Medicine.
The findings appear to be supported by a recent study in mice, which showed an increase in asthma among mouse pups born to non-asthmatic mothers but nursed by mothers with asthma.
Keep Breastfeeding, Expert Says
Boushey, who is a past president of the American Thoracic Society, agrees that it is too soon to tell mothers with asthma to limit breastfeeding based on this study.
"There is no question that breastfeeding is the way to go for the first three months of life," he says.
He adds that keeping asthma under control with adequate medication while breastfeeding is also critical. Many women limit or stop using inhaled corticosteroids during this time because they believe the treatment could harm their baby.
"A tiny amount [of the medicine] may be transmitted through milk, but it is not a risk to the baby," he says.
The study did not examine whether the breastfeeding women with asthma had their asthma under control, but Boushey says it makes sense that the risk to the baby might be greater if they did not.
Corticosteroids target inflammation, which is now thought to play a critical role in asthma. One theory is that breast milk transmits hormones that promote inflammation from mothers with asthma to their babies.
If the mother's asthma is well controlled, fewer pro-inflammatory hormones may be transmitted, Boushey speculates.