Caffeine in womb linked to childhood weight gain

Children whose mothers ingested moderate to high caffeine levels while they were in the womb are more likely to have excess weight gain in early childhood, according to a large observational study.

The findings — which back general advice to limit caffeine intake while pregnant — prompted the researchers to query whether mums-to-be should stop consuming caffeine altogether.

Caffeine passes rapidly through tissues, including the placenta, and takes the body longer to get rid of during pregnancy. It has been linked to a heightened risk of miscarriage and restricted foetal growth.

To understand whether there was a ink between caffeine intake during pregnancy and excess weight gain in children, the researchers drew on almost 51,000 mother and infant pairs, all of whom were part of the Norwegian Mother and Child Cohort Study between 2002 and 2008.

At 22 weeks of pregnancy, the mums-to-be were asked to quantify their food and drink intake from among 255 items, including caffeine, using a specially adapted Food Frequency Questionnaire.

Sources of caffeine included coffee, black tea, caffeinated soft/energy drinks, chocolate, chocolate milk, sandwich spreads, desserts, cakes and sweets. Daily intake was grouped into: 0–49 mg (low); 50–199 mg (average); 200–299 mg (high); and 300 + mg (very high).

Their children’s weight, height and body length were subsequently measured at 11 time points: when they were 6 weeks old; at 3, 6, 8, and 12 months; and then at 1.5, 2, 3, 5, 7 and 8 years of age.

Excess weight gain was assessed using World Health Organization criteria, while overweight and obesity were assessed according to International Obesity Task Force criteria. Growth trajectories for weight and length/height were calculated from the age of 1 month to 8 years using a validated approach (Jenss-Bayley growth curve).

Just under half of the mums-to-be (46%) were classified as low caffeine intake; 44% as average intake; 7% as high; and 3% as very high.

The higher the intake, the greater was the likelihood that the mother was older than 30, had had more than one child, consumed more daily calories and smoked during her pregnancy. And women with a very high caffeine intake during their pregnancy were more likely to be poorly educated and to have been obese before they got pregnant.

Average, high and very high caffeine intake during pregnancy were associated with a heightened risk — 15, 30 and 66%, respectively — of faster excess growth during their child’s infancy than low intake, after taking account of potentially influential factors.

And exposure to any caffeine level while in the womb was associated with a heightened risk of overweight at the ages of 3 and 5 years, although this persisted only for those 8-year-olds whose mums had had a very high caffeine intake during their pregnancy.

Children exposed to very high levels of caffeine before birth weighed 67–83 g more in infancy (3–12 months); 110–136 g more as toddlers; 213–320 g more as pre-schoolers (3–5 years); and 480 g more at the age of 8 than children who had been exposed to low levels.

This is an observational study, so it can’t confirm causality, while questionnaires can only provide a snapshot in time of dietary behaviour.

Nevertheless, the researchers point to the large sample size, the consistency of their findings and a plausible biological explanation — foetal programming.

“Maternal caffeine intake may modify the overall weight growth trajectory of the child from birth to 8 years,” they wrote.

“The results add supporting evidence for the current advice to reduce caffeine intake during pregnancy and indicate that complete avoidance might actually be advisable,” they added.

The study has been published in the online journal BMJ Open.

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