New research suggests there is an increased risk of deadly cardiac arrests from short-term exposure to air pollution, even at concentrations that meet global standards.

Japan has carried out a nationwide study of the relationship between PM2.5 exposure and cardiac arrests. Japan may be the best country in the world for such a project, as it has superior monitoring systems, a high population density and relatively good air quality.

The study was able to use a sample three times larger than all previous research combined, and demonstrate the impacts on key groups such as the pregnant and elderly.

The study found that more than 90 per cent of out-of-hospital cardiac arrest (OHCA) events occurred at PM2.5 levels lower than the WHO guideline (and Australian standard level) for a daily-average of 25 micrograms per cubic metre (µg/m3).

As well, 98 per cent of OHCAs happened at levels lower than the Japanese or American daily standard level of 35 µg/m3.

“Out-of-hospital cardiac arrest is a major medical emergency – with less than one in 10 people worldwide surviving these events – and there has been increasing evidence of an association with the more acute air pollution, or fine particulate matter such as PM2.5,” said corresponding author Professor Kazuaki Negishi from the University of Sydney School of Medicine.

“We analysed almost a quarter of a million cases of out-of-hospital cardiac arrests and found a clear link with acute air pollution levels.”

The researchers found a 1- 4 percent increased risk associated with every 10 µg/m3 increase in PM2.5.

Put another way, Sydney has recently been experiencing increased air pollution because of bushfire smoke and, on its worst day PM2.5 surpassed the standard of 25 µg/m3 to jump to more than 500 µg/m3 in the suburb of Richmond, comparable to levels of continuous cigarette smoking.

In a hypothetical situation, if there is just a 10-unit increase in the daily average of PM2.5, it could lead to another 600 OHCAs resulting in 540 deaths (based on a 10 per cent survival rate globally).

“Our study supports recent evidence that there is no safe level of air pollution – finding an increased risk of cardiac arrest despite air quality generally meeting the standards,” Professor Negishi says.

“Given the fact that there is a tendency towards worsening air pollution – from increasing numbers of cars as well as disasters such as bushfires – the impacts on cardiovascular events, in addition to respiratory diseases and lung cancer – must be taken into account in health care responses.”

Professor Negishi, who previously conducted field work after the 2014 massive Hazelwood coal mine fire in Victoria, said that where cardiovascular impacts were concerned, those generally at risk  were the elderly.

“If you’re young and healthy, there should be no immediate risk of devastating consequence.”

However, he says these findings are only in relation to the short-term, and that the effects can last for up to five years.

The paper concludes that there is an “urgent” need to improve air quality.

“As no boundary exists in air quality among countries, a global approach to tackle this crucial health issue is necessary for our planet,” the authors state.

The full report is accessible here.