A German study has found that pregnant women who use parabens – chemicals widely used as preservatives in cosmetics, foods and drugs – could increase the risk of their children being overweight.
The study, published in Nature Communications, suggests weight gain may be caused by epigenetic changes that limit the ability to feel full after eating.
The team, led by Irina Lehmann from the Berlin Institute of Health, analysed 629 mums and their babies who took part in the LINA study (Lifestyle and Environmental Factors and their Influence on Newborns Allergy) between 2006 and 2008.
LINA tested whether pollutants such as tobacco smoke could affect babies. Crucially, it also measured the mothers’ exposure to parabens.
Parabens are antibacterials used in cosmetics such as moisturisers, shampoos and shaving cream. The agents are also found in baked goods, jams and other foods.
In 1995 parabens were put on the US Food and Drug Administration’s “Generally Recognised as Safe” (GRAS) list but, more recently, questions have been raised about a link to breast cancer.
The chemicals are classed as endocrine disruptors and can mimic the action of the female hormone oestrogen, potentially relevant for hormone-sensitive cancers.
Lehmann’s team found women who used “leave on” (as opposed to “rinse off”) skin products containing parabens had urine levels up to three times higher than women who used paraben-free products.
Then they went on to look at how the children’s weight tracked.
Between the ages of two and eight, the team found, kids of mums exposed to higher levels of parabens in pregnancy had more than double the odds of being overweight at any point.
The findings came, however, with riders.
The effect was only seen with two out of the five parabens studied, known as iso-butyl paraben (iBuP) and n-butyl paraben (nBuP). And when the researchers did a further statistical breakdown the weight gains were most pronounced in girls.
Intrigued by the result, Lehmann’s group devised a mouse study to see what might be causing it.
They injected nBuP under the skin of pregnant mice, which gave them urine levels of the paraben comparable to the high exposure human mums. Then they waited to see what happened to the mouse bubs.
Quite a bit, it turned out.
Pups of paraben-treated mothers were fatter at all points during the observation period of 12 weeks. But, again, the effect was only seen in females.
Wondering if paraben might be working directly on fat cells, the team added nBuP to human and mouse fat cells in culture plates in the lab. But there was no effect on the growth of the fat cells.
Which left the live prospect that paraben could be affecting appetite itself.
The team homed in on a structure in the mouse brain called the hypothalamus. It’s an area rich in receptors for leptin, a hormone that goes up after eating to tell the brain you’re full.
It seemed they had found their smoking gun.
For leptin to deliver the “I’m full” message it has to turn on production of a peptide called pro-opiomelanocortin (POMC) in the hypothalamus. If POMC isn’t there you don’t feel full and you get fat. The paraben babies, it turned out, had less POMC, ate more and were heavier.
When the team did a deep dive into the genetics, they found an epigenetic “gene switch” called methylation was the likely culprit. How did they know for sure? When the team blocked methylation in the baby mice whose mums got paraben, it put a lid on the weight gain.
“With our mouse experiment, we demonstrated that… foetal development seems to be a sensitive time window for nBuP exposure with respect to body weight regulation,” they conclude.
There are, however, reasons to take the findings cautiously.
“In previous studies, it was found that mouse physiology may not be identical to humans when it comes to paraben metabolism,” says Alex Polyakov, Consultant Obstetrician and Gynaecologist at the Royal Women’s Hospital in Melbourne, who was not involved in the study.
“Therefore the mechanism of paraben effect on the risk of obesity in humans may be different,” he says.
And questions remain unanswered: for example, why females are affected disproportionately. The authors speculate it may be linked to the female hormone oestrogen.
Nonetheless, Polyakov sees reason to tread carefully.
“At this time, it would be advisable for pregnant women to avoid cosmetic compounds that contain paraben. Complete avoidance of paraben is not possible as its use is so widespread, but avoiding non-essential exposure seems like a prudent and easily achievable goal,” he says.