It's often one of the first questions a woman asks her physician when she learns she's pregnant: Can I keep drinking coffee? Soon-to-be moms are generally told by doctors not to drink more than a cup or two of coffee a day, a recommendation in line with a 2010 review concluding moderate caffeine consumption doesn't promote premature births or miscarriages or harm fetal growth. But a new study in mice offers the controversial suggestion that at larger doses, caffeine can impair memory and increase the risk of having seizures.
The study authors are quick to note that the findings may not hold in humans but the work may prompt a closer look at the world's most common psychoactive drug.
To date, no large-scale study in people has found any negative effect of caffeine exposure on fetal brain development, says Kimford Meador, a neurologist at Emory University in Atlanta. One reason for that could be that few high-quality studies exist because of the challenges of teasing apart the effects of caffeine from other variables affecting pregnant women, such as nutrition, stress and other drug use, he says. Considering that a 20-ounce coffee at Starbucks contains 410 mg of caffeine — more than twice the dose recommended for pregnant women — it's probably time to take a closer look, Meador says.
One of the ways that caffeine speeds up brain activity in adults is by blocking the activity of a neurotransmitter called adenosine, which acts as a brake on neuronal firing and makes us sleepy. Carla Silva, a neuroscientist at the University of Coimbra in Portugal, was studying the role of adenosine in fetal brain development when an experiment occurred to her: Why not use caffeine to study how adenosine alters brain development?
Silva decided to focus on a small subpopulation of a type of cells called GABA neurons, which regulate the flow of information in the brain by keeping the electrical impulses in check. Without enough GABA neurons to balance the brain's electrical activity, disorders such as epilepsy can result.
Over the course of early brain development in mammals, GABA neurons migrate from a transitory, heart-shaped embryonic structure called the ganglionic eminence to the hippocampus, a key to memory and learning.
Silva laced the drinking water of female mice 15 weeks prior to pregnancy with enough caffeine to mimic the blood concentration that a human would get from drinking about three cups of coffee a day.
After the mouse pups were born, Silva and her colleagues examined slices of brain tissue to see if being exposed to caffeine had altered the GABA neurons' maturation or migration. At six days after birth, the drug-exposed mouse pups had 41 percent fewer GABA neurons in the hippocampus, the authors reported in Science Translational Medicine. The numbers of GABA neurons in the hippocampus were similar in non-drug exposed and drug-exposed pups a few months later, however, suggesting that the cells had simply been slow to arrive. "It was quite surprising to find this delay in migration," because similar effects have been seen in animal models of cocaine and amphetamine exposure, Silva says.