Pregnant women are typically advised not to consume more than 200 milligrams of caffeine – or two average cups of coffee – a day, yet a new study in the journal BMJ Evidence-Based Medicine indicates that even this may cause harm to a fetus. After conducting a review of all the available evidence on the subject, study author Jack James of Reykjavik University concludes that there is in fact no safe level of caffeine that can be consumed during pregnancy.
To conduct his research, James analyzed the findings from 37 previous observational studies and a further 17 meta-analyses, all of which examined the potential link between caffeine and negative pregnancy outcomes. These included miscarriage, stillbirth, low birth weight, preterm birth, childhood acute leukemia, and childhood overweight and obesity.
The 37 observational studies yielded a total of 42 different findings, 32 of which supported the notion that consuming caffeine during pregnancy significantly increases the risk of a negative outcome. Meanwhile, 14 of the 17 meta-analyses were “unanimous” in concluding that maternal caffeine consumption is associated with higher rates of miscarriage, stillbirth, low birth weight, and childhood acute leukemia.
Overall, an association was found between caffeine and all of the listed negative outcomes apart from preterm birth. Crucially, findings indicated no minimum threshold of consumption below which these associations were absent, meaning that no amount of caffeine is risk-free.
While further research is needed in order to fully determine how the caffeine harms fetuses, it is already known that caffeine readily crosses the placenta. Furthermore, fetuses and newborns generally lack the enzymes that are required to metabolize caffeine, which could partially explain why they are so heavily affected by it.
According to James, expectant mothers have for decades been misled about the dangers of caffeine during pregnancy, with much of the blame for this resting with the International Life Sciences Institute (ILSI).
In his write-up, he explains how the ILSI was established by soft drink manufacturers in the late 1970s after the FDA threatened to add a health warning to products containing caffeine. When concerns were later raised about the safety of caffeine during pregnancy, the ILSI supported the publication of a raft of scientific papers depicting caffeine as safe while portraying any evidence to the contrary as flawed and unreliable.
Regardless of how the current guidelines came to exist, this latest study is unambiguous in its conclusion that “the cumulative scientific evidence supports pregnant women and women contemplating pregnancy being advised to avoid caffeine.”