Exposure to air pollution before pregnancy linked to higher childhood obesity risk, study finds

A recent study involving over 5,000 mothers and their children has revealed a significant link between exposure to air pollution during the three months before pregnancy and an increase in children’s body mass index (BMI) and associated obesity risk factors up to the age of two. The findings, supported by the National Institute of Environmental Health Sciences, were published in the journal Environmental Research.

While previous research has established connections between air pollution exposure during pregnancy and various health challenges in children, such as respiratory conditions and a heightened risk of chronic diseases, limited attention has been given to the preconception period. This timeframe, which typically refers to the three months before pregnancy begins, is critical as environmental exposures during this stage can influence the health of sperm and eggs during their final developmental phases.

In one of the largest studies of its kind, researchers from the Keck School of Medicine of USC, Duke University, and Fudan University in Shanghai examined data from 5,834 mother-child pairs recruited from maternity clinics across Shanghai. The study found that higher exposure to PM2.5, PM10, and NO2—key pollutants—prior to pregnancy was associated with an increase in children’s BMI or BMIZ, a standardised score comparing a child’s BMI to peers of the same age and sex.

“These findings imply that the three months before conception are important, and that people who plan to bear children should consider taking measures to lower their air pollution exposure to reduce their children’s risk for obesity,” said Dr Jiawen Liao, a postdoctoral research associate in population and public health sciences at the Keck School of Medicine and the study’s lead author.

Subtle but Significant Increases

The research team, led by Dr Weili Yan and Dr Guoying Huang from the Children’s Hospital of Fudan University, took advantage of a unique opportunity to begin collecting data even before pregnancy started. This allowed for the examination of preconception environmental exposures in an unprecedented way.

Using advanced machine learning models developed by Dr Jim Zhang of Duke University, the researchers estimated daily pollution exposure levels at participants’ home addresses. The models incorporated satellite data, pollutant simulations, and meteorological variables to calculate exposure to PM2.5 (fine particulate matter), PM10 (larger particulate matter), and NO2 (a gas largely emitted by motor vehicles).

Following the births, the researchers tracked the children’s weight and height at three-month intervals until the age of two using electronic medical records. This data was then used to measure growth rates of weight, BMI, and BMIZ. By comparing individuals with relatively low exposure (25th percentile) to those with higher exposure (75th percentile), the team quantified the impact of air pollution on children’s outcomes.

A higher level of preconception exposure to PM2.5 was linked to a 0.078 increase in child BMIZ at age two. Similarly, PM10 exposure correlated with a 0.093 kg/m² increase in BMI. From six months onward, children exposed to elevated levels of all three pollutants demonstrated higher growth rates in weight, BMI, and BMIZ.

“The magnitude is small, but because air pollution is widespread and everybody is exposed, the risk of air pollution exposure on children’s obesity risk may be substantial and may start before their mothers’ pregnancy,” explained Dr Zhanghua Chen, an assistant professor of population and public health sciences at the Keck School of Medicine and the study’s senior author.

Public Health Implications

Although this study is observational, meaning it does not prove causation, its findings underscore the potential risks of air pollution exposure during the preconception period. The researchers emphasised that individuals can take proactive steps to mitigate potential harm.

Suggested measures include wearing a mask or staying indoors during periods of poor outdoor air quality and using air purifiers to improve indoor air conditions. While the study primarily focused on mothers, researchers noted that men planning to conceive could also benefit from adopting these precautions.

Looking ahead, the team at the Keck School of Medicine, including Dr Liao and Dr Chen, is embarking on a new study to monitor preconception air pollution exposure in Southern California. Additionally, they are testing the effectiveness of indoor air purifiers in reducing the risk of heart and metabolic problems in the general population.

This comprehensive study highlights the critical importance of the preconception period for long-term child health, offering new insights into how air pollution may contribute to obesity risk.