Babies exposed to moderate or high levels of caffeine in the womb have a higher chance of being overweight in early childhood, the research says.
The findings call into question NHS guidelines which say expectant mothers can safely consume up to two cups of coffee a day.
Researchers looked at the link between caffeine intake during pregnancy and the weights of children up to the age of 8.
Studying 51000 mother and infant pairs in Norway between 2002 and 2008, they measured the expectant mothers’ daily intake of caffeine - found in chocolate, tea and many soft drinks as well as coffee - at 22 weeks of pregnancy. More than four in 10 were classed as having an average caffeine intake, drinking the equivalent of up to two cups of coffee a day, while 7% were classed as high intake (up to three cups) and 3% were considered to have a “very high” intake (three or more cups).
Just under half of the mothers-to-be were classified as low caffeine intake, drinking the equivalent of half a cup of coffee.
Their children’s weight and height were measured at 6 weeks old, at 3, 6, 8, 12 and 18 months old, and then at 2 years and every year up to age 8. Those whose mothers had been classed as average caffeine consumers were 15% more likely to be heavier - but not taller - than those whose mothers avoided caffeine, the researchers found. This correlation grew to 30% among the children of high caffeine consumers, and 66% among the children of very high consumers, according to the study in medical journal BMJ Open.
Children of very high caffeine consumers weighed up to 8g more between 3 and 12 months, rising to 453g more at age 8.