A significant reduction in bronchitic symptoms in children both with and without asthma in Southern California appears to be associated with lower ambient air pollution levels, according to a study published in JAMA.

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Asthma and respiratory problems may worsen with air pollution.

Bronchial and respiratory problems constitute a significant public and clinical health problem, with asthma affecting 6.3 million children in the US, or 8.6% of American children.

Asthma is responsible for 10.5 million physician visits each year and 1.8 million visits to emergency departments.

Ambient air pollutants are known to exacerbate bronchitic symptoms.

Air pollution has been high in Southern California, because of emissions from cars and other vehicles, industry, large ports and complex atmospheric reactions.

Since 1992, thanks to a range of policies and strategies designed to decrease air pollution, air quality has improved significantly.

Kiros Berhane, PhD, of the University of Southern California in Los Angeles, CA, and colleagues have been investigating the correlation between improvements in air quality in Southern California and bronchitic symptoms in children.

The study involved 4,602 children, aged from 5-18 years, in three cohorts. The average age was 8 years at baseline. Around half were girls and 45% were Hispanic white, and 19% had asthma at the age of 10 years.

The cohort studies were carried out from 1993-2001, from 1996-2004 and from 2003-2012 in eight communities in Southern California.

Researchers used information provided by parental reports or self-reports by the children on two or more annual questionnaires, and they monitored air quality in the areas where the children lived. This enabled them to estimate the impact of changes in pollution levels on bronchitic symptoms.

The questionnaire asked whether children of specific ages experienced bronchitic symptoms during the previous 12 months, defined as a daily cough for 3 months in a row, or congestion or phlegm that was not related to a cold or a period of bronchitis.

Results revealed substantial reductions in bronchitic symptoms, especially in communities where the air quality levels showed the most improvement. Children with asthma experienced a 32% decrease in symptoms, and in those without asthma, the prevalence of symptoms fell by 21%.

During follow-up, the trend persisted at the ages of 10, 13 and 15 years.

A significant drop in bronchitic symptoms occurred in places where there was a decrease in ambient concentrations of nitrogen dioxide, ozone and particulate matter with an aerodynamic diameter less than 10 µm (PM10) and less than 2.5 µm (PM2.5).

More significant reductions in bronchitic symptoms were seen in boys and among children from households with dogs.

The results confirm those from a Swiss study, carried out from 1992-2001, in which 9,591 children experienced significant decreases in respiratory symptoms as air quality improved moderately.

The authors note that limitations of the study include the use of questionnaire-based reporting of symptoms, which can be relatively imprecise when assessing health outcomes.

The authors conclude:

While the study design does not establish causality, the findings support potential benefit of air pollution reduction on asthma control.”

Recently, Medical News Today reported on research indicating that air pollution, which is estimated to cause 7 million early deaths each year worldwide, can pose a particular risk to women with diabetes.