Dr. Dwyer and his colleagues now drew the records for more than 90,000 of the men and women who had worn the trackers, skipping anyone with a known history of heart disease when they joined the study. They divided them into four groups, depending on how many minutes, in total, they moved every week, and how much of this activity was moderate, such as walking, or relatively vigorous, like jogging, as verified by their trackers.
Finally, the researchers gathered data from hospitals and death records about who, among the 90,000 volunteers, developed heart disease in the years after joining the study, and began crosschecking their diagnoses against their activity habits.
To no one’s surprise, being active was protective against heart disease. People in the least-active group, who rarely walked around or formally exercised, were more than twice as likely to have heart disease now as the most-active men and women. Just moving from the least-active group to the not-quite-as-inactive group dropped the risk of heart disease by almost 30 percent, even when the researchers controlled for body composition, smoking, socioeconomic status and other factors.
The researchers also found no upper limit to the benefits. The men and women who moved the most, walking as much as 1,100 minutes a week, or more than two hours a day (a total that included both their actual exercise and everyday activities like grocery shopping or doing housework), while also often working out intensely for 50 minutes or more a week, showed no increased risk for heart problems. Instead, this group enjoyed the greatest risk reductions, with both men and women showing about equal benefits.
The results “provide even stronger evidence than has been available previously” that “physical activity, including vigorous physical activity, is important for reducing the risk of cardiovascular disease,” Dr. Dwyer says. The benefits were “about double what had been found with most self-report studies.”
This study is associational, though, showing that active people happen also to be people with healthy hearts. It does not prove that walks and other activities directly strengthen people’s hearts, only that the two are linked. Dr. Dwyer also points out that the number of people in the study who completed extremely high amounts of intense activity was small, so it remains conceivable that long-term, intense exercise might, at some point, stop being good for hearts. That possibility requires more scrutiny, he says.
But for most of us, he says, increasing our exercise “to much higher levels or more vigorous levels” should substantially reduce our chances, later, for heart disease
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