Air pollution before conception may increase child BMI

In a study of more than 5,000 mothers and their children, exposure to air pollution during the three months before pregnancy predicted higher child body mass index (BMI) and related obesity risk factors up to two years of age. Findings from the study, which was supported by the National Institute of Environmental Health Sciences, were published in the journal Environmental Research.

Past research has linked air pollution exposure during pregnancy to a broad range of health problems in children, including respiratory issues and a higher risk for chronic diseases such as obesity and heart problems. But few studies have focused on the preconception period, typically defined as the three months before a pregnancy begins. Environmental exposures during this timeframe can affect the health of sperm and eggs, which are in their final stages of growth.

In one of the largest studies to date of preconception environmental exposures, researchers from the Keck School of Medicine of USC, Duke University and Fudan University in Shanghai, China studied 5,834 mother-child pairs recruited from maternity clinics in Shanghai. They found that greater exposure to PM_2.5, PM₁₀ and NO₂ before pregnancy was linked to increases in BMI or BMIZ, a standardized score that shows how a child's BMI compares to others 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."

Jiawen Liao, PhD, Postdoctoral Research Associate, Population and Public Health Sciences, Keck School of Medicine

Small but substantial changes

For the study, the field team, led by Weili Yan, PhD, and Guoying Huang, PhD, of the Children's Hospital of Fudan University, recruited and enrolled 5,834 women who visited 28 maternity clinics across Shanghai. This provided a rare opportunity: the ability to start collecting data before pregnancy even began.

To calculate air pollution exposure during the preconception period, the researchers developed state-of-the-art machine learning models. Led by Jim Zhang, PhD, of Duke University, they used a combination of satellite data, pollutant simulations and meteorological factors to estimate daily pollution exposure at each participant's home address. They calculated levels of PM_2.5 and PM₁₀, two types of fine particulate matter, and NO₂, which is mostly emitted by automobiles.

After birth, researchers also collected electronic medical records data of children's weight and height at three-month intervals until age two. They used this data to calculate growth rate of weight, BMI, and BMIZ.=

They then compared participants with a relatively low exposure level (the 25^th percentile of the cohort) to those with a relatively high exposure level (the 75^th percentile of the cohort) to quantify how air pollution exposure was linked to different child outcomes.

A higher level of exposure to PM_2.5 during the preconception period was associated with a 0.078 increase in child BMIZ at age two. A higher level of exposure to PM₁₀ was associated with a 0.093 kg/m² increase in BMI at age two. From six months onward, children with higher preconception exposure to all three pollutants had higher weight, BMI and BMIZ growth rates.

"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," said Zhanghua Chen, PhD, an assistant professor of population and public health sciences at the Keck School of Medicine and the study's senior author.

Precautions for the public

The study is observational, so more research is needed to determine whether air pollution exposure before pregnancy directly affects childhood obesity risk. But the findings suggest that people can take action now to minimize potential harm to themselves and their children, the researchers said.

Measures include wearing a mask or staying inside as much as possible when outdoor air quality is poor, as well as using an air purified indoors. While the study focused on mothers, men who plan to conceive may benefit from taking similar precautions.

At the Keck School of Medicine, Liao, Chen and their colleagues are planning a new study to monitor preconception air pollution exposure in Southern California. They are also testing an intervention that uses indoor air purifiers to reduce the risk of heart and metabolic problems among the general population.