High caffeine levels in womb linked to overweight children

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Although this study can not prove that caffeine itself causes kids to gain excess weight, it begs the question whether women should avoid caffeine altogether during pregnancy, Papadopoulou pointed out.

"Caffeine in utero may change how the brain develops", Bodnar said by email.

Existing guidelines in Australia and New Zealand recommend limiting caffeine intake while pregnant, but the Norwegian researchers are telling mothers to go cold turkey.

Dr Papadopoulou said earlier studies had linked caffeine to childhood obesity but this was by far the biggest and most thorough of its kind.

Caffeine passes rapidly through the placenta and has been linked to an increased risk of miscarriage and restricted fetal development, previous research has found.

The researchers used data on nearly 51,000 mother and infant pairs from a Norwegian health study between 2002 and 2008 and identified a link between caffeine during pregnancy and excess weight gain in children.

Just 7 per cent of the women had high intake, at 200 to 299 milligrams, and only 3 per cent had "very high" caffeine intake of more than 300 milligrams daily, researchers report in BMJ Open.

This persisted for eight year olds whose mothers had a very high caffeine consumption in pregnancy - more than three cups. For most of the kids, researchers estimated growth through age 8 based on children's development over their first 12 months of life.

Average, high, and very high caffeine intake during pregnancy were associated with an increased risk - 15 per cent, 30 per cent, and 66 per cent respectively - of "excess growth" during their child's infancy compared to children born to mothers who had a low caffeine intake during pregnancy.

Dr Clovis Palmet, Senior Monash University Fellow and Burnet Institute head of immunometabolism and inflammation, said: "The researchers provided no evidence of a causal link between prenatal exposure to caffeine and early childhood obesity".

The researchers are confident in their results because of the large sample size, the consistency of the findings and a plausible biological explanation - foetal programming.

Most health authorities suggest that pregnant women limit their caffeine intake since, after ingestion, caffeine is readily absorbed into the bloodstream and distributed to the tissues.

At 22 weeks, the women surveyed were asked to record their food and drink intake. Coffee, black tea, caffeinated soft/energy drinks, chocolate, chocolate milk, sandwich spreads and desserts, cakes and candies were all considered sources of caffeine. Tea has 75mg, a can of cola 40mg and one 250ml can of energy drink up to 80mg. Researchers assessed infant weight gain by calculating the difference in sex-adjusted World Health Organization weight-for-age z scores between birth and age 1 year, using reported weights, and determined childhood overweight, including obesity, at two time points at ages 3 and 5 years and once at age 8 years.

Women who consume at least 200 mg of caffeine per day during pregnancy are more likely to have offspring with excess growth in infancy and overweight in childhood, and the risk rises with increasing caffeine intake, according to an analysis of a Norwegian pregnancy cohort.

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