Giving antibiotics to treat infections in newborn baby boys – but not girls – during the first two weeks of their lives can cause them to have lower weight and be shorter up to the age of six, according to a joint Israeli-Finnish study just published in the prestigious journal Nature Communications under the title: “Neonatal antibiotic exposure impairs child growth during the first six years of life by perturbing intestinal microbial colonization.” Why newborn boys and girls differ in their reaction is not known. 

By contrast, the study showed significantly higher body mass index (BMI) in both boys and girls following antibiotic use after the neonatal period and within the first six years of life. The research team at Bar-Ilan University (BIU) in Ramat Gan near Tel Aviv and in Turku University Hospital in Finland may be the result of changes in the development of the gut microbiome. Later in infancy and childhood, antibiotic use has been linked to increased risk of overweight and obesity.

Exposure to antibiotics in the first days of life is believed to affect various physiological aspects of development in the newborn. “Antibiotics are vitally important and life-saving medications in newborn infants. Our results suggest that their use may also have unwanted long-term consequences that need to be considered,” said Prof. Omry Koren of BIU’s Azrieli Faculty of Medicine, who led the study together with Prof. Samuli Rautava of the University of Turku and Turku University Hospital. The study was additionally conducted by researchers at BIU’s Louzoun Lab, the Max Rubner Institute in Germany, the University of Trento (Italy) and Migal Israel.

Newborn infants are highly susceptible to invasive bacterial infections, and suspected infection is one of the most common reasons for admission in a neonatal unit. The incidence of blood culture confirmed early-onset neonatal sepsis – a type of bloodstream infection in a newborn baby such as meningitis, pneumonia, pyelonephritis (bacterial infection of the kidneys) or gastroenteritis, they wrote. “According to current recommendations, all newborns with clinical signs suggesting bacterial infection, in addition to selected high-risk infants, receive antimicrobial therapy. Thus, a considerable number of newborn babies are treated with antibiotics during the first days of life.

The team investigated the effects of antibiotic exposure in newborns on 12,422 children born between 2008 and 2010 at the hospital in Finland.  The babies had no genetic abnormalities or significant chronic disorders affecting growth and did not need long-term antibiotic treatment. Antibiotics had been administered within the first 14 days of life to 1,151 (9.3%) of the neonates in the study.

The authors found that boys exposed to antibiotic treatment exhibited significantly lower weight as compared to non-exposed children throughout the first six years. They also exhibited significantly lower height and BMI between the ages of two and six. This observation was replicated in a group of German babies with similar characteristics.

Antibiotic exposure during the first days of life was found to be connected with disturbances in the gut microbiome up until the age of two. Infants exposed to antibiotics during the first 14 days of life showed significantly lower amounts of beneficial bacteria in their intestinal system compared to non-exposed infants at the age of one month. Interestingly, at the age of six months, the infants treated with antibiotics reached the bacterial richness level of a control group of infants, and at the ages of 12 and 24 months, the antibiotic-treated subjects gained significantly higher levels of bacterial richness as compared to the control subjects.

In additional experiments led by PhD student Atara Uzan, the researchers showed that germ-free male mice who were given the gut microbiome of antibiotic-exposed infants also displayed growth failure. These findings suggest a potential link between neonatal antibiotic exposure and impaired childhood growth, which may be a result of alterations caused by antibiotics in the composition of the gut microbiome. The study will be followed up to investigate other potential adverse outcomes related to antibiotic exposure in newborns.