A longitudinal cohort study shows a U-shaped relationship between total physical activity and heart failure risk in men.

The 15-year study of 33,012 men, average age 60 years at baseline, showed that those who engaged in the highest levels and intensity of total physical activity had a 31% greater risk of heart failure than did those in the median activity category.

However, men who undertook the lowest levels of physical activity had up to a 69% greater risk of heart failure compared to the median activity group, according to the results, published online Aug. 12 in JACC: Heart Failure.

“The U-shaped relationship between exercise levels and the likelihood of subsequent heart failure is a unique finding and will stimulate further research in the important field of prevention,” said Dr. Christopher O’Connor , editor-in-chief of JACC: Heart Failure, who was not involved in the study.

The questionnaire-based study involved of 3,609 heart failure events, which included 3,190 first events of heart failure hospitalizations and 419 deaths from heart failure.

The study authors assigned intensity scores – defined as metabolic equivalents (MET) hours/day – to each type of physical activity, then calculated a total daily physical activity score for each individual by multiplying the intensity scores by reported duration of each activity.

Watching TV, reading, and sleep were assigned the lowest intensity MET scores, walking or bicycling were in the mid-range, and exercise was assigned the highest MET scores.

Walking or bicycling at least 20 minutes a day were associated with the greatest reductions in the risk of heart failure – 21% – compared to not walking or biking, and this type and level of activity was linked to an 8-month delay in the onset of heart failure among those who engaged in it.

The investigators also found no differences between the two groups in terms of age or education level, and the exclusion of study participants who developed heart failure in the 3 first years of follow-up did not impact results.

“When examining long-term behavior regarding walking or biking and HF [heart failure] risk, the results suggested that more recent active behavior in this PA [physical activity] domain may be more important for HF protection than past PA levels,” wrote Dr. Iffat Rahman and colleagues at the Karolinska Institute, Stockholm.

Exercising for more than 1 hour per week was linked with a 14% reduction in risk, but work occupation, household work, and physical inactivity did not affect heart failure risk ( JACC Heart Fail. 2015 Aug 12. doi:10.1016/j.jchf.2015.05.006 ).

While previous studies have shown that lower levels of physical activity increase the risk of heart failure, the authors said this was the first to show an increase in risk among individuals who undertake very high levels of physical activity.

“It is possible that substantial increase of pumping of blood by the heart could damage the cardiac muscle fibers causing damage in the myocardium,” the authors wrote.

“Moreover, adverse cardiovascular outcomes could potentially be attributed to increased oxidative stress, arterial stiffness, and coronary artery calcification.”

A similar study looking at the relationship between physical activity and heart failure in women did not find an increased risk with very high levels of physical activity, suggesting a differential effect between men and women.

There were no conflicts of interest declared.