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Small particulate matter increased risk of childhood asthma

A recent study in China reported increased risk of asthma after early-life exposure to particulate matter (PM), with smaller PM leading to a greater risk.

Small particulate matter (PM) is associated with childhood asthma, according to a recent study.

PM has been associated with disease burden worldwide, having caused an estimated 1.4 million deaths in China alone in 2019. Vulnerable populations including children are at an increased risk of respiratory disease from both short-term and long-term exposure to PM.

Of all chronic respiratory diseases, asthma is the most common in children. An increase in rates of asthma has been observed in recent years, which some investigators have attributed to environmental factors either independently or alongside genetic factors.

In China, PM1, PM with an aerodynamic equivalent diameter less than 1 μm, has contributed to about 80% of PM2.5, PM with an aerodynamic equivalent diameter less than 2.5 μm. While particle size has been associated with respiratory disease, few studies have analyzed the relationship between PM1 and childhood asthma.

Investigators conducted a cross-section study to determine PM1’s contribution to the association between PM2.5 and childhood asthma. They study took place from June 2019 to June 2020, across 7 cities in China. Participants were given a standardized questionnaire which had been validated by a pilot study, with consent given from parents or legal guardians.

Ambient PM1, PM2.5, and PM10 were estimated in 7 cities from January 2013 to December 2018. Concentration of PM1 was measured by subtracting from PM2.5, and concentration of PM2.5 was measured by subtracting from PM10. Exposure to these particles from early life was then estimated using information on birth and conception dates along with address information.

In the questionnaire, participants were asked if their children ever had doctor-diagnosed asthma and if they ever had wheezing or whistling in the chest. Covariates included child characteristics, parent characteristics, and household environment characteristics.

There were 29,418 children included in the study, about 52% of which were girls and about 48% boys. Caregivers reported wheezing in 8.6% of children, while 3.9% had been diagnosed with asthma. Of children born vaginally, 5.3% were preterm births, 3.5% low birth weight, 62.9% breastfed for more than 6 months, and 2.7% had a parental history of atopy.

Early-life exposure to PM1 had a mean of 36.7 μg/m3, PM 2.5 of 61 μg/m3, and PM10 of 110.6 μg/m3. Exposure was highest during pregnancy, decreasing during the first year of life. PM1 and PM2.5 exposure directly correlated with PM10 exposure.

For each 10-μg/m3 increase of PM1 exposure early in life, risk of childhood asthma increased by 55%. For PM2.5 exposure, risk increased by 14%. PM10 exposure was also associated with a significant increase in risk of childhood asthma.

Wheeze was only associated with early-life PM1 exposure and PM2.5 exposure. Smaller PM saw higher risks, and no response-relationship between risk of asthma and wheeze and size-segregated PM exposure was observed.

These results indicated increased risk of childhood asthma in PM1, PM2.5, and PM10 exposure early in life, with PM1 exposure seeing the greatest risk. Wheeze was also reported with PM1 and PM2.5 exposure. Investigators concluded that PM1 contributes more to childhood asthma than larger particles, and that air purification efforts are needed to reduce adverse health outcomes.


Wu C, Zhang Y, Wei J, Zhao Z, NorbäckD, Zhang X, et al. Associations of early-life exposure to submicron particulate matter with childhood asthma and wheeze in China. JAMA Netw Open. 2022;5(10):e2236003. doi:10.1001/jamanetworkopen.2022.36003