Ozone is a pollutant that is formed by chemical reactions of other pollutants in the presence of sunlight. These other pollutants are volatile organic compounds and nitrogen oxides that come from emissions from vehicle traffic, thermoelectric power plants, and other industrial activities. Exposure to ozone pollution has already been linked to damage to the heart and blood vessels, but a new study has found evidence that exceeding the ozone limit recommended by the World Health Organization (WHO) – which sets the limit at 100 µg/m3 – is associated with a significant increase in hospital admissions for myocardial infarction, heart failure and stroke.
Their findings have been published in the European Heart Journal and show that even ozone levels below the maximum indicated by the WHO were associated with worsening population health. “During this three-year study, ozone was responsible for an increasing proportion of cardiovascular disease admissions as time progressed,” said Professor Shaowei Wu of Xi’an Jiaotong University (China) and author of the study.
“Climate change, by creating atmospheric conditions that favor ozone formation, is believed to continue to raise concentrations in many parts of the world. Our results indicate that older people are particularly vulnerable to the adverse cardiovascular effects of ozone, meaning that worsening ozone pollution with climate change and the rapidly aging global population may produce even greater risks of cardiovascular disease in the future”.
Worsening of cardiovascular diseases due to ozone
The researchers examined the association between ozone air pollution and hospital admissions for cardiovascular diseases and obtained data on daily hospital admissions for cardiovascular diseases from 2015 to 2017 in 70 cities in China from the two major national health insurance systems. This included around 258 million people (18% of the country’s population).
Ozone levels of 100 μg/m3 or more were associated with a significant increase in hospitalizations for cardiovascular diseases, reaching 6.52% for myocardial infarction.
The cardiovascular diseases studied included coronary heart disease, stroke, and heart failure, and other heart problems such as angina, acute myocardial infarction, acute coronary syndrome, ischemic stroke, and hemorrhagic stroke. China’s National Urban Air Quality Real-time Publication Platform provided the data on the eight-hour maximum daily average concentrations of ozone, fine particulate matter (PM2.5), inhalable particulate matter (PM10), sulfur dioxide, of nitrogen and carbon monoxide for each of these cities.
In the 70 cities, there were 6,444,441 hospital admissions for cardiovascular diseases during the study period, and the average daily maximum eight-hour ozone concentration was 79.2 μg/m3. Exposure to ozone present in the environment was associated with an increase in these admissions for all the cardiovascular pathologies studied with the exception of hemorrhagic cerebrovascular accident, independently of other pollutants in the air.
For example, each 10 μg/m3 increase in 2-day average 8-hour peak ozone concentration was associated with a 0.40% increase in hospital admissions for stroke and 0.75% for heart attack. myocardial acute. While these figures may seem irrelevant, Professor Wu has cautioned that “it should be noted that ozone levels can rise to more than 200 μg/m3 in the summer, and these increases in hospitalizations would be amplified by more than 20 times to more than 8% due to cerebrovascular accidents and 15% due to acute myocardial infarction”.
The researchers also compared the excess risk of admission for cardiovascular disease associated with ozone concentrations at or above the WHO air quality guideline with that associated with levels below 70 μg/m3, which are typically naturally occurring and They are not related to human activity.
They found that compared with two-day 8-hour average peak concentrations below 70 μg/m3, levels of 100 μg/m3 or higher were associated with a significant increase in CVD hospitalizations, from 3.38 % for cerebrovascular accidents up to 6.52% for acute myocardial infarction. And lower concentrations of 70 to 99 µg/m3 (versus less than 70 µg/m3) were also associated with increases in hospital admissions, ranging from 2.26% for heart failure to 3.21% for coronary heart disease.
Between 2015 to 2017, 3.42%, 3.74%, and 3.02% of hospital admissions for coronary heart disease, heart failure, and stroke, respectively, were attributed to ozone pollution. When looking at each year separately, the proportions increased over time. For coronary disease, ozone was responsible for 109,400 of the 3,194,577 admissions that occurred over these three years.
“This suggests that 109,400 coronary disease admissions could have been avoided if ozone concentrations were 0 µg/m3. This may be impossible to achieve given the presence of ozone from natural sources. However, we can conclude that a considerable number of hospital admissions for cardiovascular diseases could be avoided if levels were below 100 μg/m 3 , with further reductions at lower concentrations,” concludes Professor Wu.
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