By age 9, children of smoking mothers perform at par with their classmates if they are breast-fed, according to the study by Dutch researchers at the University Hospital Groningen. However, babies of cigarette-smoking mothers tend to score poorly on standardized tests if they are bottle-fed.
"Babies are already being put in a compromised position when the mother smokes, and then to bottle-feed on top of that is like a double negative for the child," says Carol Huotari, manager of the Center for Breast-Feeding Information at La Leche League International.
Data for the study were culled from the experiences of 570 children born at one Dutch hospital between 1975 and 1978. Nine years after their birth, the children's scores on math, spelling and reading tests were collected by researchers and compared with information on the smoking and breast-feeding habits of their mothers.
To ensure that the mothers' self-reported feeding method was accurate, the team interviewed them at their time of discharge from the hospital, when their children were 9, and again when their children were 25.
The results support the new recommendations adopted by the American Academy of Pediatrics in 2001, which advise that smoking mothers should breast-feed because the benefit of nursing their child far outweighs the potential negative health effects of nicotine exposure through breast milk.
Nicotine is easily absorbed through lungs but is actually poorly transferred through the digestive system and mouth, causing babies to be only minimally exposed to the drug through breast milk, says Dr. Beth Lawrence, a professor of pediatrics and obstetrics at the University of Rochester School of Medicine.
The Dutch findings, published in the June issue of the Journal of Epidemiology and Community Health, do not provide any answers on how breast-feeding might protect infants from the cigarettes' impact.
One theory is that the long-chain polyunsaturated fatty acids found in breast milk promote brain development, say the authors.
"It's the fatty acids in human milk that enhance the brain development," agrees Huotari, which is why formula companies are now trying to harness the benefits of these unique fats by putting them in baby formula to make them more like mother's milk.
Another way that mother's milk might help an infant's cognitive development is through the nurturing act of breast-feeding itself, which may offer psychological benefits to the child, hypothesize the researchers.
But whatever the mechanism, one message is clear from the findings: Pregnant women who smoke should be encouraged to breast-feed their infants, says Lawrence.
"This suggests that for mothers who continue to smoke, it's better to breast-feed than not, and this study further confirms that," she says.