(CNN) Children's exposure to alcohol through breast milk may cause a comparable drop in their cognitive abilities, according to a study published Monday in the journal Pediatrics.
"This is the first study in which associations between alcohol exposure through breast milk and cognition in children are examined," the researchers from Macquarie University in Australia wrote in the report.
The authors obtained data from a longitudinal study, a continuous study of data over a period of time, of 5,107 Australian infants who were recruited in 2004 and evaluated every two years until age 11. Their mothers were asked about their alcohol consumption from a modified questionnaire used by the World Health Organization. They were also asked about daily cigarette smoking during pregnancy and breastfeeding. The children were quizzed on their vocabulary, nonverbal reasoning and cognitive processes.
The researchers also found that an increased maternal consumption of alcohol aligned with lower nonverbal reasoning scores in 6- and 7-year-olds who had breastfed. The same was not found in those who had never breastfed after adjusting for factors such as prenatal alcohol consumption, gender, child and maternal age, breastfeeding duration and birth weight. This lowered cognitive ability was not maintained when the children were assessed at 10 and 11 years old, the authors discovered.
"If you have a small effect to begin with and it lasts to, say, age 6 or 7, chances are by the time the child gets older, other environmental factors will start to play a bigger role," said Dr. Melissa Bartick, an assistant professor of medicine at Cambridge Health Alliance and Harvard Medical School, who was not involved in the study.
The researchers hypothesized that increased education was a possible mediator for the decreased effects of age and alcohol. The size of the relationship between alcohol exposure in breast milk and cognition was small, and they suspected that clinical implications could be limited unless mothers drank a great deal.
Smoking while breastfeeding did not appear to have any effect on cognition, the study found. Women who were breastfeeding tended to smoke fewer cigarettes daily than those who were not: 1.06 cigarettes per day, compared with 2.84.
"Just because the authors didn't find an issue with smoking doesn't mean mothers should think it's OK to smoke while breastfeeding," Bartick wrote in an email. "Remember, the authors only looked at one thing, cognition, and there are lots of toxins in tobacco smoke, and smoking around children can cause them lots of harm and just having smoke on your clothes can be harmful to the health of others, as well as to the mother. Smoking is not good in any circumstance, for baby or mother."
Additionally, 91.7% of the children in the study had at some point been breastfed, but just 8.2% had not.
About 82.5% of children have ever breastfed in the United States, according to the US Centers for Disease Control and Prevention.
"It's a very different culture than the United States," said Dr. Diane Spatz, a professor at the University of Pennsylvania School of Nursing who did a visiting professorship in Australia in 2007 but who was not involved in the new study. "The breastfeeding rates are much higher in Australia than they are in the United States. Also I think alcohol consumption is different too, is what I observed while I was there."
About one in 10 pregnant women in the United States drinks alcohol, reports the CDC. One study reported that 40% to 80% of women in the UK, Australia and New Zealand drank alcohol while pregnant.
"I think we really need to emphasize to that when you are pregnant, you shouldn't be consuming alcohol," said Spatz, who is also director of the lactation program at the Children's Hospital of Philadelphia. "When you are breastfeeding, you shouldn't be consuming alcohol. If you want to have an occasional adult beverage, that's OK, but it shouldn't be a regular intake of alcohol."
The CDC states that not drinking alcohol is the safest option for breastfeeding mothers, but moderate alcohol consumption -- defined as up to one drink a day -- is not known to be harmful to infants, particularly if the mother waits at least two hours before nursing. Breast milk has the highest alcohol content about a half-hour or hour after the woman consumes a drink, and the alcohol is usually still detected for two to three hours after per drink.
"We tell moms, 'you know, If you are feeling tipsy, drunk, woozy, any effects of alcohol, you shouldn't be caring for your infant, nor should you be breastfeeding your infant,' " Spatz said. "That's when a mom will pump and discard her milk. But that's for getting rid of the milk for comfort's sake."
"Pumping and dumping" does not lessen the amount of alcohol in breast milk any faster, the CDC says. The alcohol in a mother's milk is basically what is in her bloodstream.
The new study is interesting but leaves questions unanswered because it does not detail the effect of just alcohol consumption in lactation, Spatz said. A high level of alcohol exposure in pregnancy could also affect a child's cognition. And there is no distinction made in whether mothers breastfed exclusively or whether there was any kind of supplementation.
Another limitation of the study was that individual people weren't studied, just a large population, Bartick said.
She noted that the researchers "had to do what's called imputation of the missing data, which means that whenever you have to [replace] missing data, it means it's going to be less accurate than if you had all the data there."
"I think the study is helpful, but it doesn't definitely answer the question. The question is, how much, if any, alcohol is safe during lactation?" Bartick said. "I would advise mothers to avoid alcohol and not to use alcohol, not to use beer to try to increase their milk supply. I think that's safe to advise."
Dr. Lauren M. Jansson, director of pediatrics at the Center for Addiction and Pregnancy and an associate professor of pediatrics at the Johns Hopkins University School of Medicine, wrote in a commentary published with the study, "Previous recommendations that reveal limited alcohol consumption to be compatible with breastfeeding during critical periods of development, such as the first months of life, may need to be reconsidered in light of this combined evidence."
More research is needed to fully understand the effects of maternal consumption of alcohol and other substances like marijuana on breastfed children, Jansson said. A deeper dive into specific psychosocial risks for breastfeeding and non-breastfeeding mothers who use various substances is also suggested.
But the study serves as an "an important step in our understanding of the complex neurobiological and developmental vulnerability of the substance-exposed child," she added.