Study suggests there is 'no safe level' of caffeine consumption for pregnant women

EDMONTON — Women who are pregnant or trying to conceive may want to avoid their morning cup of joe according to new research that suggests safe levels of caffeine consumption during pregnancy is a myth.

An analysis of observational studies, published in the journal BMJ Evidence Based Medicine Monday, found evidence to suggest that maternal caffeine consumption may be associated with negative pregnancy outcomes, warning that there is “no safe level of consumption” for pregnant mothers.

Pregnant women are often told that consuming a small amount of caffeine daily will not harm their baby.

The Public Health Agency of Canada recommends that pregnant or breastfeeding women and women who are planning to become pregnant limit their caffeine intake to less than 300 milligrams per day, which works out to a little over two eight-ounce cups of coffee.

However, study author, Reykjavik University professor Jack James, says this relaxed position needs to change.

“It is important for the public to understand that caffeine is not the benign substance it is often portrayed to be. Unfortunately, the position to date of health authorities has been disappointing in this regard,” James told CTV News via email.

“The idea, promoted by many health authorities, that there is a safe level of maternal caffeine consumption is a myth. That relaxed position is not consistent with scientific evidence and it is a position that must change.”

Through database searches, James identified 1,261 English language peer-reviewed articles linking caffeine and caffeinated beverages to pregnancy outcomes. Those studies were then narrowed down to 48 original observational studies and meta-analyses published in the past two decades reporting one or more of six major negative pregnancy outcomes: miscarriage, stillbirth, low birth weight, preterm birth, childhood acute leukemia, and childhood obesity.

A total of 42 findings were reported in 37 observational studies. Of those, 32 found that caffeine significantly increased the risk of adverse pregnancy outcomes and 10 found no or inconclusive associations.

According to the analysis, James says there is substantial evidence of an association between maternal caffeine consumption and negative pregnancy outcomes, specifically miscarriage, stillbirth, low birth weight, childhood acute leukemia and childhood obesity, but not preterm birth.

“Chronic exposure to any chemical during pregnancy is cause for concern. There should be no exception simply because that chemical, caffeine, happens to be widely consumed," he said, noting that caffeine should be given special attention thanks to its widespread consumption.

James explains that when caffeine is consumed during pregnancy -- whether in coffee or other natural forms such as chocolate -- it crosses the placenta exposing the fetus to the substance.

Fetuses are largely incapable of metabolizing caffeine. Studies have shown that caffeine can interfere with fetal heart function and oxygenation.

“Considering what is known about the pharmacology of caffeine, the fact that the drug is widely consumed during pregnancy, and the many studies (over more than four decades) that have revealed associations between maternal caffeine exposure and negative pregnancy outcomes, it is not surprising that when all the findings are brought together the results point strongly to caffeine being a significant source of harm,” he said.

James notes that not all human studies have reported "significant" associations between caffeine exposure and negative pregnancy outcomes​, adding that the results of these studies could be impacted by other factors and does not point to the direct link between caffeine consumption and negative pregnancy outcomes.

However, he notes that there is no evidence to suggest that caffeine benefits mother or baby.

“Even if the evidence were merely suggestive, and in reality, it is much stronger than that, the case for recommending caffeine be avoided during pregnancy is thoroughly compelling,” James said.