The first evidence that exceeding the World Health Organization (WHO) ozone limit is associated with significant increases in hospital admissions for heart attack, heart failure and stroke is published today in European Heart Journal, a journal of the European Society of Cardiology (ESC). Even ozone levels below the WHO maximum were associated with worsening health.
“During this three-year study, ozone was responsible for an increasing proportion of admissions for cardiovascular disease as time progressed,” said study author Professor Shaowei Wu from Xi’an Jiaotong University in China. “It is believed that climate change, creating atmospheric conditions that favor ozone formation, will continue to increase concentrations in many parts of the world. Our results show that the elderly are particularly vulnerable to the adverse cardiovascular effects of ozone, meaning that worsening of ozone pollution with climate change and a rapidly aging world population may create even greater risks of cardiovascular disease in the future.”
Ozone is a gas and the main air pollutant in photochemical smog. Ozone pollution is different from the ozone layer, which absorbs most of the sun’s ultraviolet radiation. Ozone pollution is formed when other pollutants react in the presence of sunlight. These other pollutants are volatile organic compounds and nitrogen oxides emitted by motor vehicles, power plants, industrial boilers, refineries, chemical plants, and biomass and fossil fuel combustion plants. Previous studies have suggested that ozone pollution damages the heart and blood vessels, but there is limited and inconclusive evidence on its effect on cardiovascular disease risk.
This study examined the relationship between ambient ozone pollution and hospital admissions for cardiovascular disease. Data on daily hospital admissions for cardiovascular disease during 2015–2017 in 70 cities in China were collected from the two major national health insurance systems. During the study period, the two databases covered about 258 million people in the 70 cities, equivalent to more than 18% of China’s population. Cardiovascular disease types included coronary heart disease, stroke, and heart failure, as well as subtypes such as angina, acute myocardial infarction, acute coronary syndrome, ischemic stroke, and hemorrhagic stroke.
The maximum eight-hour daily concentrations of ozone, fine particulate matter (PM2.5), respirable particulate matter (PM10), sulfur dioxide, nitrogen dioxide, and carbon monoxide were obtained for each city from the China National Urban Air Quality Publishing Platform in real time.*
During the study period, there were 6,444,441 hospital admissions for cardiovascular disease in the 70 cities, and the eight-hour average daily peak ozone concentration was 79.2 μg/m3. Ambient ozone exposure was associated with increased hospital admissions for all cardiovascular diseases studied except hemorrhagic stroke, independent of other air pollutants. For example, every 10 µg/m3 An increase in mean peak ozone concentration over two eight-hour days was associated with a 0.40% increase in hospital admissions for stroke and a 0.75% increase in acute myocardial infarction.**
Professor Wu said: “Although these increases appear modest, it should be noted that ozone levels can rise to higher than 200 µg/m.3 in the summer, and these increases in hospitalizations would increase more than 20-fold to over 8% for stroke and 15% for acute myocardial infarction.”
The researchers also estimated the excess risk of admission for cardiovascular disease associated with ozone concentrations above the WHO air quality guideline (100 µg/m3) compared to levels below 70 μg/m3. Ozone levels below 70 µg/m3 they are mostly natural and not due to human activity. Compared to two-day eight-hour peak concentrations below 70 μg/m3levels of 100 µg/m3 or higher were associated with significant increases in hospital admissions for cardiovascular disease, ranging from 3.38% for stroke to 6.52% for acute myocardial infarction. However, lower concentrations of 70 to 99 µg/m3 (vs. below 70 µg/m3) were also associated with increases in hospital admissions, ranging from 2.26% for heart failure to 3.21% for coronary artery disease.
During 2015-2017, 3.42%, 3.74% and 3.02% of hospitalizations for coronary heart disease, heart failure and stroke, respectively, were due to ozone pollution. When each year was analyzed separately, the proportions increased over time. For coronary heart disease, ozone was responsible for 109,400 of the 3,194,577 admissions over three years. Professor Wu said: “This suggests that 109,400 coronary heart disease admissions could have been avoided if ozone concentrations were 0 µg/m.3. This may be impossible to achieve given the presence of ozone from natural sources. However, we can conclude that a significant number of hospital admissions for cardiovascular disease could be avoided if levels were below 100 µg/m3with further decreases at lower concentrations.”
In an accompanying article, Professor Thomas Münzel and colleagues said: “Projections for Europe suggest that ozone will play a more dominant role as a health risk factor in the future due to climate change with increasing temperatures and, consequently , the increasing photochemical ozone formation. The strong link between climate change and air quality means that reducing emissions in the long term to tackle global warming will play a key role in alleviating ozone pollution and improving the air we breathe.”
*Eight-hour mean concentrations were calculated from hourly mean concentrations. The maximum eight-hour average is the highest value between 00:00 and 23:59. **Two-day average refers to the day of hospital admission and the previous day.