Air pollution may negate heart benefits of physical activity

Engaging in prolonged and strenuous exercise on days when air pollution levels were high appeared to be detrimental to heart health in young adults in a real-world, population study from South Korea.

In the analysis of health insurance data from close to 1.5 million people between the ages of 20-39 years, declining physical activity was associated with an increased risk for cardiovascular disease (CVD) compared to maintaining physical activity in those routinely exposed to low-to-moderate levels of air pollution (PM2.5 or PM10). However, large increases in physical activity occurring in high-pollution environments was also associated with elevated CVD risk in the study, which is among the first to examine the combined effects of air pollution and change in physical activity patterns on CVD risk in young adults.

Among study participants exposed to high levels of PM 2.5 air pollution, those who increased their exercise dramatically between two screening periods conducted several years apart had a 33% increased risk of CVD compared to those who were physically inactive or did not increase their exercise.

“Until now, there has been little information on the trade-off between the cardiovascular health benefits of physical activity and the potential harmful effects of increased exposure to air pollution during outdoor physical activity,” wrote researcher Seong Rae Kim, of Seoul National University College of Medicine, and colleagues in the European Heart Journal.

The researchers added that no previous study has examined the “trade-off between the potential cardiovascular harm caused by a decrease in physical activity and the benefits to cardiovascular health from decreased exposure to air pollutants due to decreased outdoor physical activity.”

In a press statement, Kim added that reducing air pollution could “maximize the health benefits of exercising in young adults.”

“These are people who tend to engage in physical activity more than other age groups while their physical ability is at its best,” Kim said. “If air quality is not improved this could result in the incidence of cardiovascular diseases actually increasing despite the health benefits gained from exercise.”

The researchers studied National Health Insurance Service (NHIS) of South Korea data on 1.47 million young adults (age 20-39 years) without a prior history of cardiovascular disease who underwent two consecutive biennial health examinations during the first (2009 and 2010) and second (2011 and 2012) health screening periods. Participants were followed from the years 2013 through the end of 2018.

Air pollution exposure was estimated by the annual average cumulative level of particulate matter, while physical activity was calculated as minutes of metabolic equivalent tasks per week (MET-min/week) based on the two consecutive health examinations from 2009 to 2012 and taking into count exercise frequency, intensity, and duration.

Using the responses to the NHIS survey from the consecutive biennial health examinations (2009–2010 and 2011–2012), the researcher extracted the weekly frequencies of light-intensity (≥30 min/day; e.g. light exercise, walking for leisure), moderate-intensity (≥30 min/day; e.g. fast/brisk walking, tennis, slow cycling), and vigorous-intensity (≥20 min/day; e.g. running, aerobics, fast cycling, mountain hiking) physical activity. Ratings of 2.9, 4.0, and 7.0 MET were applied to light, moderate, and vigorous physical activity, respectively.

The researchers categorized individuals into four groups of 0, 1–499, 500–999 (current guideline recommendations), and ≥1000 MET-min/week of physical activity during the two consecutive screening periods, and the MET-min/week values for the first and second screening periods were used to determine changes in physical activity.

Among participants exposed to low-to-moderate levels of air pollution, those who increased their physical activity from 0 MET-min/week (physically inactive) to ≥ 1000 MET-min/week (PM2.5 adjusted HR [aHR] 0.73; 95% CI 0.52– 1.03; P for trend 0.04) had a reduced risk of cardiovascular disease compared with participants who were continuously physically inactive.

Among the findings:

  • Compared with the participants exposed to low-to-moderate levels of PM2.5 or PM10 who continuously engaged in 1000 MET-min/week or more of physical activity, those who decreased their physical activity from ≥1000 MET-min/week to 1–499 MET-min/ week (PM10 adjusted hazard ratio [aHR] 1.22; 95% CI, 1.00–1.48) or became physically inactive to 0 MET-min/week (physically inactive; PM10 aHR 1.38; 95% CI, 1.07–1.78) had an increased CVD risk (P for trend <0.01).
  • Among groups exposed to high levels of air pollution, increasing physical activity from physically inactive to ≥1000 MET-min/week tended to negate the risk-reducing effect of physical activity on CVD (PM2.5 aHR 1.33; 95% CI 0.96–1.84).
  • For coronary heart disease and stroke, the association of changes in physical activity strata with these outcomes stratified by level of air pollution showed similar trends.

“We found a significant effect modification of the association between changes in physical activity and CVD risk by the level of exposure to PM2.5 or PM10,” the researchers wrote.

Study limitations cited by the researchers included the lack of specific information on whether exercise was conducted inside or outside, but they noted that studies in South Korea show that most physical activity occurs outdoors.

  1. Engaging in prolonged and strenuous exercise on days when air pollution levels were high appeared to be detrimental to heart health in young adults in a real-world, population study from South Korea.

  2. Large increases in physical activity occurring in high-pollution environments was associated with elevated cardiovascular risk in the study, which is among the first to examine the combined effects of air pollution and change in physical activity patterns on CVD risk in young adults.

Salynn Boyles, Contributing Writer, BreakingMED™

Funding for this research was provided by the Korea Centers for Disease Control and Prevention and the Korea Safety Health Environment Foundation.

The researchers declared no relevant conflicts related to this study.

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