Drinking just half a cup of coffee during pregnancy can knock nearly an inch off a child's height by the time they are eight, according to new research. The discovery is based on almost 2,500 boys and girls in the US. It adds to evidence mums-to-be should abstain.
Corresponding author Dr Katherine Grantz said: "Though the clinical implications of an approximately 2cm difference are unclear, our findings for height are similar in magnitude to those of children whose mothers smoked during pregnancy." Current NHS guidelines recommend pregnant women should have less than 200mg a day - about two cups of instant coffee.
Dr Grantz, of the Eunice Kennedy Shriver National Institute of Child Health and Human Development in Maryland, said the phenomenon was identified well below this level. She added: "We consistently observed shorter height - which has been associated with increased risk of multiple cardiometabolic diseases."
They include obesity and diabetes. Modest coffee consumption in pregnancy has been linked to lower birth weight. Dr Grantz said: "Higher maternal caffeine concentrations were associated with shorter stature.
"Our findings indicate maternal caffeine consumption is associated with long-term decreases in child height." In the first study of its kind Dr Grantz and colleagues analysed data from two separate cohorts - tracking participants into primary school.
She said: "Children of women with low measured caffeine during pregnancy were shorter than the children of women who consumed no caffeine during pregnancy - with increasing gaps in height through age eight years. "These findings suggest small amounts of daily maternal caffeine consumption are associated with shorter stature in their offspring that persist into childhood."
The potential mechanism is unclear. But caffeine is a neural stimulant not metabolised by the foetus that accumulates in its tissue. Coffee is the world's most popular beverage - regularly drank by up to eight in ten pregnant women.
Dr Grantz said: "It is important to determine whether caffeine exposure in the womb has long-term growth implications in offspring."
Previous studies looking at caffeine's effects on pregnancy relied on women to report how much they consumed daily. The study in JAMA Network Open used blood samples taken during pregnancy from to determine participants' exact levels of caffeine and its metabolite, paraxanthine.
