WEDNESDAY, July 18, 2018 (HealthDay News) -- Everyone knows that exercise is good for your heart, but what if your only option is to run or walk through smoggy city streets? Does it still pay off in the long run?
Yes, contends a nearly 20-year study.
"Air pollution isn't an excuse to skip exercise. Even in areas with pollution, exercise still helps," said Dr. Peter Mercurio. He's a cardiologist with Northern Westchester Hospital in Mount Kisco, N.Y., who reviewed the findings.
Although the study didn't look at people with respiratory diseases, folks who have conditions such as asthma should still avoid exercising outdoors when pollution levels are high, according to the American Lung Association. High air pollution can trigger asthma attacks.
But for most healthy people, the study findings suggest that cycling, gardening and playing sports can lead to a healthier heart and a reduced risk of first heart attack or heart attack recurrence, even in a polluted city.
Heart disease is a leading cause of death in the United States and Europe, according to the researchers and the U.S. Centers for Disease Control and Prevention. Traffic-related air pollution is known to increase the risk of heart attacks, and deaths from heart attacks and strokes. In fact, exposure to air pollution is likely responsible for as many as 4.2 million deaths globally.
Physical activity, on the other hand, can reduce the risk of heart attack. Active commuting -- walking or biking -- has been linked to an 11 percent reduction in the risk of heart attack or stroke, the study authors noted.
But other recent research concluded that the benefits of physical activity were cancelled out by the harmful effects of air pollution, the researchers added.
The new study, led by Nadine Kubesch, a researcher at the University of Copenhagen, included nearly 52,000 people born in Denmark. The participants were living in Copenhagen or Aarhus, and were aged 50 to 64 when the study began in the early to mid-1990s.
The volunteers answered questions about their diets, exercise habits and other factors that might contribute to heart disease risk, such as smoking, weight, education, employment and marital status.
The researchers gathered information on motor vehicle air pollution (NO2) at the volunteers' homes by reviewing national air pollution data.
During the study, which lasted almost two decades, there were nearly 3,000 first heart attacks and 324 recurrent heart attacks, the investigators found.
Participating in all four activities -- playing in sports, biking, walking and gardening -- for four or more hours a week cut the risk of a recurrent heart attack in half. Moderate cycling for four or more hours a week dropped the risk of recurrent heart attack by 31 percent, the study found.
Overall, the researchers found that playing sports was linked to a 15 percent reduced risk of heart attack. Biking was associated with a 9 percent reduced risk of heart attack, and gardening was tied to a 13 percent decreased risk of heart attack. Walking didn't significantly reduce the odds of heart attack. And although the study found these associations, it did not prove that exercise caused heart risks to drop.
Living in areas with high pollution was linked to a 17 percent increase in the risk of a first heart attack and a 39 percent increase in the risk of recurrent heart attack.
However, air pollution didn't appear to dampen the benefits of exercise, the researchers said.
Dr. Len Horovitz, a pulmonary specialist at Lenox Hill Hospital in New York City, said the study suggests that "poor air quality does not cancel out the benefits of exercise. It is still beneficial to exercise, in spite of the pollution."
Mercurio said the study still left a lot of questions unanswered. The researchers measured air pollution at home -- but what about exposure at work? And, did the study participants live and work in the same areas for the 20 years of the study, he asked.
Horovitz also noted that previous research has shown that air pollution can contribute to hardening of the arteries, and people have been advised to avoid exercising at peak pollution times because of this.
In cities larger than Copenhagen or Aarhus, such as New York, Los Angeles and Chicago, the effects of pollution are likely stronger, Mercurio added. He said it's always a good idea to avoid pollution when you can.
"Exercising in less polluted areas is better," he said. So, if you live in a city, you might be better off exercising in a park instead of on the street.
The study was published online July 18 in the Journal of the American Heart Association.
Learn more about air pollution's effect on your health from the World Health Organization.