Caffeine passed from a nursing female mouse slows down pups’ brain development.
Doctors usually warn pregnant women against having more than 200 mg of caffeine per day—the equivalent of about 1.5 cups of brewed coffee. This level of the stimulant is considered safe because it doesn’t induce premature births or other pregnancy complications, according to the American College of Obstetricians & Gynecologists.
Researchers wondered, though, whether a mother’s caffeine intake of approximately 200 mg can have more subtle effects on human fetuses when the world’s most popular drug is absorbed in the womb or when transferred from mother to baby during breast-feeding.
Seeking answers, a team of researchers led by Christophe Bernard of the French Institute of Health & Medical Research studied pups born to female mice that drank caffeine each day from the time they mated until their babies were weaned. The female mice received a daily dose of caffeine equivalent to three or four cups of coffee per day for a human.
When the team examined the brains of the caffeine-exposed pups days after birth, they observed a delay in the migration of certain nerve cells compared with a control group of baby mice (Sci. Transl. Med. 2013, DOI: 10.1126/scitranslmed.3006258). During brain development, Bernard says, “some neurons are born in specific brain regions,” but they eventually have to move to other areas. The team thinks that “caffeine puts a brake on the migration of these neurons” in mice, he says.
The brains of caffeine-exposed pups were also more excitable: The animals convulsed more often than offspring not exposed to caffeine when the researchers gave them flurothyl, a seizure-inducing compound.
“Animal studies like this one provide provocative reminders that subtle changes in developmental trajectory can produce significant changes in brain structure and function,” says Gregg D. Stanwood, an assistant professor of pharmacology at Vanderbilt University School of Medicine.
Bernard and his team are quick to point out that mice are not people, and no direct conclusions about the human health effects of caffeine can be drawn from their work. But, Bernard says, these findings should prompt further surveys of children born to regular caffeine drinkers.