Young people should avoid very strenuous physical activity on days when air pollution levels are high, according to new research from South Korea published today.
A nationwide study of nearly 1.5 million people is the first to investigate people aged between 20-39 years over several years and the findings are published in the latest edition of the European Heart Journal.
Professor Sang Min Park led the research team from Seoul National University College of Medicine, which examined information from the country’s National Health Insurance Service (NHIS) for 1,469,972 young Koreans living in cities.
The participants underwent two health examinations during two screening periods: 2009-2010 and 2011-2012 and were followed up from January 2013 to December 2018.
At each health check-up, they completed a questionnaire about their physical activity in the past seven days and this information was converted into units of metabolic equivalent task (MET) minutes per week (MET-mins/week).
The participants were divided into four groups: 0, 1-499, 500-999 and 1000 or more MET-mins/week and the researchers used data from the National Ambient Air Monitoring System in South Korea to calculate annual average levels of air pollution, in particular the levels of PM10 and PM2.5.
The amount of exposure to air pollution was categorised at two levels: low to moderate (less than 49.92 and 26.43 micrograms per cubic metre, ?m/m3, for PM10 and PM2.5 respectively), and high (49.92 and 26.46 ?m/m3 or more, respectively). [2]
First author Dr Seong Rae Kim said: “We found that in young adults aged 20-39 years old, the risk of cardiovascular diseases, such as stroke and heart attack, increased as the amount of physical activity decreased between the two screening periods in the group with low levels of exposure to air pollution.
“However, in the group with high levels of exposure to air pollution, increasing the amount of physical activity to more than 1000 MET-min/week, which is more than internationally recommended levels for physical activity, could adversely affect cardiovascular health.
“This is an important result suggesting that, unlike middle-aged people over 40, excessive physical activity may not always be beneficial for cardiovascular health in younger adults when they are exposed to high concentrations of air pollution.”
He added that it is imperative that air pollution is improved to maximise the health benefits of exercising in young adults.
During the follow-up period there were 8706 cardiovascular events and the researchers found that people exposed to high levels of PM2.5 air pollution and those who increased their exercise from 0 to 1000 MET-min/week or more between the two screening periods had a 33% increased risk of cardiovascular disease during the follow-up period compared to those who were physically inactive and did not increase their exercise.
However, the team says this result was slightly weaker than that needed to achieve statistical significance and is equivalent to an extra 108 people per 10,000 who might develop cardiovascular disease during the follow-up period.
People exposed to low to moderate levels of PM2.5 and those who increased their physical activity from none to 1000 MET-min/week or more, had a 27% reduced risk of developing cardiovascular disease compared to those who remained inactive.
Again, this result was also not statistically significant and equates to 49 fewer people per 10,000 who might develop cardiovascular disease during the follow-up period.
For low to moderate levels of PM10 air pollution, there was a statistically significant 38% or 22% increased risk of cardiovascular disease among people who started off doing 1000 MET-min/week or more and then reduced their activity to none or to 1-499 MET min/week, respectively, compared to people who maintained the same high level of activity.
Professor Sang Min Park, who led the research, said: “Overall, our results show that physical activity, particularly at the level recommended by European Society of Cardiology guidelines, is associated with a lower risk of developing heart and blood vessel disease among young adults. However, when air pollution levels are high, exercising beyond the recommended amount may offset or even reverse the beneficial effects.”
Kim SR, Choi S, Kim K et al. Association of the combined effects of air pollution and changes in physical activity with cardiovascular disease in young adults. European Heart Journal 30 March 2021; doi:10.1093/eurheartj/ehab139
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