Breast Feeding May Be Significant Source Of Infants' Exposure To Tobacco Products

Infants of mothers who smoke may receive greater exposure to the products of tobacco smoke through breast milk than through environmental exposure, according to a study led by researchers at the Massachusetts General Hospital (MGH) and Brigham and Women's Hospital (BWH). According to the report appearing in the June issue of the American Journal of Public Health, urine levels of cotinine, a substance produced by the breakdown of nicotine in the body, were 10 times higher in breast-fed children of smoking mothers than in bottle-fed children of smoking mothers.

Maria A. Mascola, MD, MPH, first author of the study says, "While we don't know for sure whether the compounds present in breast milk are related to any of the harmful health effects seen in some children of smoking women--from reduced lung function to greater incidence of asthma and other illnesses--this does stress how important it is to help mothers refrain from smoking both during pregnancy and while they are nursing." Mascola is director of Perinatal Epidemiology in the Vincent Obstetrics and Gynecology Service at the MGH.

This investigation was part of the Maternal/Infant Lung Study, a long-term project conducted by the Channing Laboratories at BWH in collaboration with the East Boston Neighborhood Health Center. The researchers examined data from 330 mother/infant pairs who received prenatal, obstetric and pediatric care through the East Boston Center, analyzing information about maternal smoking and the presence of other smokers in the home along with results of urine tests taken from the infants in the first year of life. While cotinine, the substance tested for, is not known to have any harmful effects itself, it is generally used as a marker for the presence of nicotine and other tobacco products.

As expected, cotinine levels in bottle-fed infants of smoking mothers were about eight times higher than in bottle-fed infants of non-smoking mothers. But among children of smoking mothers, infants who were breast-fed had cotinine levels ten times higher than those of bottle-fed infants. Type of feeding had no effect on the cotinine levels of infants of non-smoking mothers.

The researchers also found significantly higher cotinine levels in infants of non-smoking mothers who were exposed to tobaccco through smoking by another household member, with no difference related to feeding. For infants of smoking mothers, the presence of another smoker in the household caused a small, statistically insignificant increase in cotinine. In addition, children of mothers who smoked in the same room as their infants also had a small, statistically insignificant increase in cotinine over children of mothers who always smoked in rooms away from their infants.

"Our 10-year study has looked at a lot of factors related to the ways kids can be exposed to tobacco smoke on a prenatal and postnatal level," says John P. Hanrahan, MD, MPH, of the respiratory epidemiology section at Channing Laboratories and BWH, the study's senior author. "A lot of people have assumed that the inhalation of passive smoke is totally responsible for the adverse health effects seen in children of smoking mothers. This study has widened our view of the ways smoking may be detrimental to the health of children."

The researchers note that, while the presence of cotinine in infants' urine strongly suggests the transmission of other tobacco products from mother to infant, it is still not known which compounds are actually responsible for the observed health problems and whether they are transmitted in breast milk. Further research is required to answer those questions.

Other co-authors of the study are Helen Van Vunakis, PhD, of Brandeis University; Ira B. Tager, MD, MPH, of the School of Public Health at the University of California at Berkeley; and Frank E. Speizer, MD, co-director of the Channing Laboratory at BWH. The study was supported by a grant from the National Heart, Lung and Blood Institute.