Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. Exposure to particulate matter less than 2.5 um in diameter was identified as an environmental risk factor for pediatric asthma.

2. Family related risk factors for pediatric asthma include parental asthma, maternal smoking during pregnancy, lower parental income, and lower parental educational attainment.

Evidence Rating Level: 3 (Average)

Asthma is one of the most widespread conditions affecting children around the world. In the past, genetics were considered a significant risk factor due to children of asthmatic parents being more likely to have asthma themselves. However, rapidly increasing rates of asthma indicate that environmental and societal factors may be important to consider as well. Specifically, environmental factors such as air pollution and urbanisation, and family factors such as exposure to smoking, socioeconomic status (SES), and parental income, have all been associated with pediatric asthma. The current case-control study used a nationwide approach, evaluating 3 192 785 Danish children, born between 1997 and 2014 to investigate how air pollution and family factors are associated with asthma onset and persistent wheezing. Out of these, 122 842 were identified as asthmatic, meaning they were diagnosed with asthma or received at least two asthma-related medications between the ages of 1 and 15. Each asthmatic child was matched randomly with 25 non-asthmatic controls, with the same sex and a birth date within a week. For family factors, the results showed higher rates of asthma in children whose parents also had asthma, and whose mothers had smoked while pregnant (adjusted hazard ratio 2.29, 95% CI 2.22-2.35; HR 1.20, 95% CI 1.18-1.22 respectively). As well, lower rates of asthma were found in children of parents with high income and high educational attainment (HR 0.85, 95% Ci 0.81-0.89; HR 0.72, 95% CI 0.69-0.75 respectively). In terms of air pollution, exposure to particulate matter less than 2.5 um in a diameter was the only factor to be positively associated with asthma and persistent wheezing across all models. For every increase in pollutant concentration by 5 ug/m3, the HR was 1.05 (95% CI, 1.03-1.07). Study findings reinforce existing evidence associating low SES and increased air pollution with increased incidence of asthma.

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