Drinking two or more cups of coffee a day during pregnancy can damage the baby’s liver, according to research.
Too much caffeine can slow down the development of the organ and increase a child’s risk of developing fatty liver disease or diabetes in adulthood.
A study in rats, which showed 120 mg caffeine per day, was sufficient to lower the level of a hormone vital for liver growth.
And the same effect may also apply to humans, the scientists suggest, when women drink caffeinated beverages during pregnancy.
This is a “common” habit, the researchers said, with coffee, tea and soft drinks popular with expectant mothers.
One expert said, however, that research was too weak to prevent women from drinking tea and coffee during pregnancy, and there was no guarantee of any effect on humans.
Researchers at Wuhan University in China tested their theory by feeding caffeine to pregnant rats and testing their babies.
They found that those who fed them caffeine – starting with a dose of 120 mg per day (an average cup of coffee contains about 95 mg) – had fewer healthy offspring.
In the study, scientists gave rats amounts of caffeine up to the equivalent of nine cups of coffee.
The caffeine caused a decrease in a hormone called insulin-like growth factor (IGF-1), which promotes growth in the body and can lower blood sugar levels.
As a result, babies were found to have a “compensatory” growth boost in their liver after birth, which could lead to abnormal development, the team said.
NHS guidelines recommend pregnant women not to drink more than 200 mg of caffeine per day – about two cups of soluble coffee.
It says that too much caffeine can cause a low birth weight for a baby and can also increase the risk of the mother miscarrying.
Our results suggest that prenatal caffeine causes an excess of stress hormone activity in the mother,” said Dr. Yinxian Wen, an author of the study.
This could inhibit IGF-1 activity for liver development before birth.
However, postpartum compensation mechanisms occur to accelerate growth and restore normal liver function as IGF-1 activity increases and signalling of stress hormones decreases.
The increased risk of fatty liver disease due to prenatal caffeine exposure is most likely a consequence of this increased compensatory postnatal IGF-1 activity.
Non-alcoholic fatty liver disease is a disease caused by a fatty deposit in the liver – a healthy liver should contain almost no or no fat.
The disease is most common in people who are overweight.
It can affect liver function and increase the risk of type 2 diabetes, hypertension and kidney disease in adults.
Dr Wen said: “Our work suggests that prenatal caffeine is not good for babies, and although these results still need to be confirmed in humans, I would recommend women to avoid caffeine during pregnancy.
However, an expert who was not involved in the research said that Dr Wen’s conclusion went one step too far.
Dr Michelle Bellingham, a scientific lecturer at the University of Glasgow, said: “While this is an interesting and extensive study…and builds on the previous knowledge that high maternal caffeine consumption can have harmful effects on the fetus, we must remember that these results occur in rats.
Caffeine may not have exactly the same effects as humans due to inherent species differences (e.g. differences in metabolism, genetic and ecological influence).
We need more research on humans before we know whether these results are transferable to humans – some pregnant women can avoid caffeine that would not do harm, but that would be precautionary and not justified by this study alone”.
Another researcher, Dr. Sarah Stock of the University of Edinburgh, said she could not see the relevance.
Dr. Stock added, “This study shows that rats that receive large amounts of caffeine during pregnancy have puppies that are smaller and have some changes in liver development.
Although this is an interesting study in an animal model, the relevance to human pregnancy is not very clear. The Koffeindosen used in the study were much higher than the current pregnancy recommendations.
The British guideline states that