A Better Start National Science Challenge’s research into the association between antibiotic exposure and childhood obesity is one of the largest studies of its kind ever conducted. It used a sample size of nearly 290,000 children and their mother’s (151,359 children and 132,852 mothers).

51% of the children were boys. Antibiotics exposure was common, with at least once course dispensed to 35.7% of mothers during pregnancy and to 82.3% of children in the first two years of life.

The objective of the study was to assess whether antibiotic exposure during pregnancy and/or in early childhood was associated with the development of childhood obesity.

Obesity is a significant problem in New Zealand and affects 1 in 3 adults and 1 in 9 children. Antibiotics have historically been used as growth-promoting agents in farm animals and research in animals has shown that use of antibiotics led to obesity. However, evidence in humans is inconsistent.

Numerous studies have reported a positive association between antibiotic exposure and development of childhood obesity. However, there are several studies which showed that antibiotics are not associated with the development of childhood obesity. In these studies, the majority looked at the association between childhood exposure and very few examined exposure in mothers during pregnancy on obesity.

There is some concern that previous positive studies have not adequately accounted for potential confounding factors including genetic and environmental factors. In particular, very few studies have studied siblings or twins and the small studies that did include these analyses reported no associations between antibiotic exposure and the risk of childhood obesity.

This study, which has been published in the JAMA Network Open, used national data from New Zealand to assess whether antibiotic exposure in women during pregnancy and/or in their children early in life was associated with the likelihood of childhood obesity at 4 years of age. In addition, to address the influence of environmental and genetic factors, the study examined these associations among siblings and twins.

Antibiotics lead to negative changes in the gut microbiome[i], which has been proposed to lead to the development of obesity. The mechanisms for this are still unclear but could be attributed to the ability of gut bacteria to increase energy protection and alter our metabolism and immune function.

However, results from this study indicate there is no association between antibiotic exposure in mothers during pregnancy and in early childhood on the development of childhood obesity at age 4 years, once the influence of environmental and genetic factors have been controlled.

“We wanted to better understand the role that antibiotics play in the development of obesity and to investigate for possible confounding factors that may have influenced these previous results,” says lead researcher, Dr Karen Leong, PhD candidate and Clinical Research Fellow at the Liggins Institute at the University of Auckland.

There were no associations between prenatal and early childhood antibiotics exposure and the odds of developing childhood obesity. “While judicious prescription and use of antibiotics is vital, we concluded that antibiotics are unlikely to be a major contributor to childhood obesity,” says Dr Leong.

“Although antibiotics are not associated with childhood obesity, antibiotics usage in New Zealand is extremely high, especially during early childhood and it is important to ensure proper antibiotic stewardship among healthcare professionals and the community at large,” says Professor Wayne Cutfield, Director of A Better Start National Science Challenge.

A Better Start has supported intervention strategies to combat obesity; specifically the potential role of the gut microbiome in treating obesity and metabolic diseases, which will soon be published.

Background Information:
Data from children born between July 2008 and June 2011 was obtained from the B4 School Check, a national health screening programme that records height and weight of 4-year-old children in New Zealand. This data was linked to antibiotics (from pharmaceutical records) dispensed to women pre-conception and in all three trimesters of pregnancy, and to their children from birth until age 2 years. The data was analysed on the whole population (n=150,699), siblings (n=30,696), and twins (n=4,188).

[i] Microbiomes are microorganisms that reside in the gut consisting of bacteria, viruses, and fungi.

Listen to Professor Wayne Cutfield being interviewed by RNZ’s First Up’s Lydia Batham about the Associations of Prenatal and Childhood Antibiotic Exposure with Obesity at Age 4 Years study on Thursday 23 January 2020.