Research out this week may one day complicate the standard advice given to pregnant people about drinking coffee. The study found that people with higher levels of caffeine consumption during their first trimester of pregnancy went on to have slightly shorter children on average than those with less caffeine in their system. This association was seen even with modest amounts of caffeine below the maximum daily dose recommended by experts. But it’s not clear yet whether the connection raises the risk of relevant health problems, such as obesity.
The study was led by researchers from the National Institutes of Health. They analyzed data from two previous long-running observational studies of pregnant people that also kept track of their children’s health through age 8. As part of these studies, the mothers had their levels of caffeine and paraxanthine (a byproduct of caffeine) measured through blood samples collected in the first trimester of pregnancy. They then compared the height and weight outcomes of children born to these parents.
Across both datasets, children born to mothers who had the lowest caffeine intake were a bit taller on average than children born to those who had the most caffeine. This height gap was apparent by age 4 and increased up through age 8. Depending on the dataset, this difference ranged from 1.5 to 2.2 centimeters by age 8, or about 0.59 to 0.86 inches. Importantly, this relationship between caffeine and height was even seen in the dataset where people’s median caffeine consumption was estimated to be less than 50 milligrams a day—below the limit of 200 milligrams of caffeine recommended for pregnant people by organizations such as the American College of Obstetricians and Gynecologists. The findings were published Monday in JAMA Network Open.
Other studies have found a link between caffeine consumption above 200 milligrams a day (about one to two cups of coffee) during pregnancy and negative health outcomes in children, including reduced birth weight. But the authors were inspired to conduct this research after their previous study last year suggested that the size of newborns might be affected by even smaller doses of caffeine, a hunch that’s been further strengthened by these new findings.
They also note that there is a biologically plausible explanation for this effect. Caffeine can cross over through the placenta and reach the fetus, and neither the placenta nor the fetus produce an enzyme that allows fully developed humans to break down caffeine, meaning that it could accumulate in fetal tissue. From there, the caffeine might be able to interfere with how fetuses respond to hormones that regulate their growth, the authors theorize.
At the same time, trying to figure out caffeine’s health effects has never been easy. This study does have an advantage over many others, since it was able to directly measure how much caffeine people were consuming, rather than relying on self-reports, which are notoriously inaccurate. But it’s still only finding a correlation between caffeine and children’s heights, not directly showing that a causal relationship exists. And there’s the larger question of whether this effect, assuming it’s real, would have any negative health implications down the line outside of making someone slightly shorter than they might have been.
Theoretically, a disruption in the growth development of fetuses could raise the risk of other health issues in later life. And shorter height has been tied to a higher future risk of conditions like heart disease and diabetes. But the authors didn’t find a clear link between caffeine consumption and other early markers of these issues in these children, like higher body weight. Other research, meanwhile, has not found a link between negative health outcomes in pregnancy and caffeine consumption below 200 milligrams a day, and some research has even suggested that low doses of caffeine might lower the risk of certain conditions such as gestational diabetes. And for non-pregnant people, most research continues to indicate that caffeine consumption is a net positive, at least in moderation.
The authors and outside experts acknowledge that more studies, perhaps including some that can similarly track the outcomes of older children, will be needed to find out if the current caffeine recommendations for pregnant people should be changed.
“Although the results of the study are interesting, further research is needed to support the findings and as the researchers conclude, the clinical implication of this height difference is unclear and warrants future investigation,” Helena Gibson-Moore, a scientist with the British Nutrition Foundation not affiliated with the research, said in a statement provided by the Science Media Center.