Exceeding the World Health Organization (WHO) ozone limit is associated with substantial increases in hospital admissions for heart attack, heart failure and stroke, according to a new study.
The first evidence making this association is published in the European Heart Journal.
Even ozone levels below the WHO maximum were linked with worsened health, the study said.
“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 of Xi’an Jiaotong University, China.
“It is believed that climate change, by creating atmospheric conditions favouring ozone formation, will 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 rapid ageing of the global population may produce even greater risks of cardiovascular disease in the future,” said Wu.
Ozone is a gas and the main air pollutant in photochemical smog. Ozone pollution is different to 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 which are emitted by motor vehicles, power plants, industrial boilers, refineries, chemical plants, and biomass and fossil fuel burning facilities.
Previous studies have suggested that ozone pollution harms the heart and blood vessels, but there is limited and inconclusive evidence about its influence on the risk of cardiovascular disease.
This study examined the association between ambient ozone pollution and hospital admissions for cardiovascular disease, it said.
Data on daily hospital admissions for cardiovascular disease during 2015 to 2017 in 70 cities in China were collected from the two main national health insurance systems.
During the study period, the two databases covered approximately 258 million, 25.8 crore, people across the 70 cities, equivalent to more than 18 per cent of China’s population.
The types of cardiovascular disease included coronary heart disease, stroke and heart failure, plus subtypes such as angina, acute myocardial infarction, acute coronary syndrome, ischaemic stroke and haemorrhagic stroke.
Daily eight-hour maximum average concentrations of ozone, fine particulate matter (PM2.5), inhalable particles (PM10), sulphur dioxide, nitrogen dioxide and carbon monoxide were obtained for each city from the China National Urban Air Quality Real-time Publishing Platform, the study said.
During the study period, there were 64,44,441 hospital admissions for cardiovascular disease in the 70 cities and the average daily eight-hour maximum ozone concentration was 79.2 microgram per cubic metre (ug/m3).
Exposure to ambient ozone was associated with increased hospital admissions for all cardiovascular diseases studied except haemorrhagic stroke, independent of other air pollutants.
For example, each 10 ug/m3 rise in the two-day average eight-hour maximum ozone concentration was associated with a 0.40 per cent increase in hospital admissions for stroke and 0.75 per cent for acute myocardial infarction.
“Although these increments look modest, it should be noted that ozone levels may surge to higher than 200 ug/m3 in summer, and these increases in hospitalisations would be amplified by more than 20 times to over 8 per cent for stroke and 15 per cent for acute myocardial infarction,” said Wu.
During 2015 to 2017, 3.42 per cent, 3.74 per cent and 3.02 per cent of hospitalisations for coronary heart disease, heart failure and stroke, respectively, were attributable to ozone pollution.
When each year was analysed separately, the proportions rose with time.
For coronary heart disease, ozone was responsible for 109,400 of 3,194,577 admissions over three years.
“This suggests that 109,400 coronary heart disease admissions could have been avoided if ozone concentrations were 0 ug/m3. This may be impossible to achieve given the presence of ozone from natural sources.
“However, we can conclude that considerable numbers of hospital admissions for cardiovascular disease could be avoided if levels were below 100 ug/m3, with further reductions at lower concentrations,” said Wu.
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