Infants who receive antibiotics before 6 months of age may be at increased risk for obesity during childhood, according to data from a cohort of 10,000 children in the United Kingdom.
A study based on analysis of those data was published online August 21 in the International Journal of Obesity.
Lead author Leonardo Trasande, MD, MPP, associate professor of pediatrics and environmental medicine at New York University School of Medicine in New York City, and colleagues note that in recent years, researchers have gained new understanding about the human microbiome -- the myriad bacterial flora that reside in the body and aid in metabolism, cell differentiation, and immune response.
"Knowledge of the importance of the microbiome in human development raises new issues about antibiotic use in children, since such exposures may disrupt the microbial ecology," the authors write.
They say that even though populations of bacterial flora in adults are relatively stable, that might not be the case with young children, whose bacterial flora may be more variable and susceptible to negative effects from antibiotics and other factors.
To look further into how antibiotic exposure in early life might affect body weight later on, the researchers evaluated longitudinal birth cohort data from 11,532 children who were included in the Avon Longitudinal Study of Parents and Children (ALSPAC). ALSPAC is a population-based study of children born in Avon, United Kingdom, during 1991 and 1992. All of the children included in this analysis weighed at least 2500 g at birth.
Over time, data on the children were collected via hospital records, surveys, clinical visits, and laboratory tests. The researchers especially focused on exposure to antibiotics during 3 periods: before 6 months of age, at 6 to 14 months of age, and at 15 to 23 months of age. They also checked data on the children's weight up through their seventh year of life.
The researchers found that on average, children exposed to antibiotics early on weighed more. "This longitudinal study found that early life antibiotic exposure was associated with subsequent increases in body mass," the authors write.
However, they say that of the 3 periods studied, only exposure during the first 6 months of life was consistently linked to increased body mass.
"At 38 months, children who had been exposed to antibiotics during this earliest period had significantly higher standardized [body mass index (BMI)] scores, and were 22% more likely to be overweight than children who had not been exposed," they write.
However, exposure to antibiotics after 6 months of age was not consistently associated with an increased BMI, the researchers say. Children exposed to antibiotics during their first 6 to 14 months of life showed no association, whereas children exposed at age 15 to 23 months showed significant associations, with higher BMIs at 7 years of age but not when they were assessed in the years leading up to that time.
All the assessments were based on statistical models that took a variety of potential factors into account, including diet, physical activity, and the weight of the children's parents.
The authors emphasize that their findings, although showing an association between early antibiotic exposure and childhood obesity, do not prove a causal link. Other limitations include potential recall bias, possible confounding factors not accounted for in multivariable analysis, and limited generalizability.
In addition, the ALSPAC sample is from the early 1990s; antibiotic exposure was significantly less frequent at that time than it is today, explain the authors. Average use, the researchers say, has increased 4.3% annually since 2000 in the United Kingdom.
"While effects of early exposures are modest at the individual level, they could have substantial consequences for population health," the authors note. "Given the prevalence of antibiotic exposures in infants, and in light of growing concerns about childhood obesity, further studies are needed to isolate effects and define life-course implications for body mass and cardiovascular health," they conclude.
Source: Int J Obes. Published online August 21, 2012.