Boys grow at slower rate if they were given antibiotics as newborns | Boys grow at slower rate if they were given antibiotics as newborns

young boy

Newborn boys given antibiotics are more likely to see slower growth

Kamil Macniak/Alamy

If boys get antibiotics in the first two weeks of life their weight and height gain is more likely to be below average – but the effect isn’t seen in girls.

Some babies are given antibiotics to treat suspected bacterial infections and to prevent sepsis. Samuli Rautava at the University of Helsinki in Finland and his colleagues explored the long-term effects of giving antibiotics to newborns within two weeks of birth.

They recorded the growth of 12,422 children from birth to six years of age. All were born between 2008 and 2010 at the Turku University Hospital in Finland. Of these, 1151 babies were given antibiotics within the first 14 days of life because doctors suspected bacterial infection.


Babies given antibiotics were more likely to have a significantly lower height and weight throughout their first six years of life than those who weren’t given antibiotics – but this was only observed in boys, not girls. “We showed for the first time that antibiotic exposure during the first days of life has long-term effects,” says Rautava.

The researchers suspect that the antibiotics cause long-term changes in the babies’ gut microbiome, resulting in reduced growth.

Bacteria in the gut are “a forgotten organ”, says co-author Omry Koren at the Bar-Ilan University in Israel. They help digest our food, train our immune system and protect us from harmful, foreign bacteria.

“When we use antibiotics to kill bacteria that may cause disease, we inadvertently kill other good bacteria as well,” says Rautava. This change in gut microbiome seems to be the driver of the impaired growth in young boys following antibiotic use.

To test this idea, the team implanted microbes from babies’ faeces that were and weren’t given antibiotics into mice. They observed the same results – male mice, but not female mice, that were given microbiota from antibiotic-treated babies were much smaller.

Exactly why the effect is seen only in males is still being investigated. Martin Blaser at Rutgers University, New Jersey, suggests it may be connected to sex-related differences in intestinal gene expression – males and females experience genetic differences in the intestine as early as two days after birth.

The long-term effects of a course of antibiotics need to be investigated, but Rautava says we shouldn’t forget that the drugs are necessary to prevent severe bacterial infection in babies. “Antibiotics save lives,” he says.

Journal reference: Nature Communications, DOI: 10.1038/s41467-020-20495-4

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