Does Exercise Actually Increase Your Risk of Atrial Fibrillation?

Data from a large cohort of Swedish men suggests that regular vigorous exercise starting around age 30 may increase the risk of atrial fibrillation (AF), particularly among those who stop exercising later in life.

A research team from Karolinska University Hospital in Stockholm collected information from a self-administered 1997 questionnaire about physical activity levels of 44,410 atrial fibrillation-free men, aged 45—79 years (mean age=60).

Survey participants reported (from memory) how much time they had spent per week engaged in vigorous exercise at four ages: 15, 30, 50 and whatever their age when filling out the survey. They also reported how much time they spent daily at baseline on leisurely exercise such as walking or bicycling.

The researchers matched that data with information from the Swedish National Inpatient Register to see which patients developed atrial fibrillation and then used Cox proportional hazards regression models to estimate relative risks (RR) of various long-term exercise patterns with 95% confidence intervals (CIs), adjusted for potential confounders.

No level of vigorous exercise at 15 predicted significantly higher levels of atrial fibrillation, but vigorous exercise at 30 produced a U-shaped pattern for atrial fibrillation risk. People who performed moderate amounts (2-3 hours a week) had lower risk levels than those who either did less than 1 hour per week or more than 5 hours per week.

Researchers found that performing too much exercise at 30 was actually riskier than performing too little. Indeed, the research team, whose findings just appeared in the journal Heart, calculated a RR of 1.19 (95% CI 1.05 to 1.36) of developing atrial fibrillation in men who had exercised for >5 hours per week at age 30 compared with those who exercised <1 hours per week.

The risk was particularly high among men who were active early in life and then became sedentary in later years. Men who exercised >5 h/week at age 30 and quit exercising later in life (<1 h/week at baseline) faced a 1.49 RR of developing atrial fibrillation (95% CI 1.14 to 1.95) compared to the cohort as a whole.

But frequent exercise did not always increase atrial fibrillation risk. To the contrary, walking or bicycling at baseline was inversely associated with risk of atrial fibrillation.

Men who walked or biked an hour or more per day (so at least 7 hours a week) faced a 0.87 RR of developing atrial fibrillation (95% CI 0.77 to 0.97) compared to those who rarely walked or biked at baseline. That association remained almost unchanged even after excluding men with previous coronary heart disease or heart failure at baseline (corresponding RR 0.88, 95% CI 0.77 to 0.998).

Moreover, walking and biking at any age seemed to reduce the risk not only of atrial fibrillation but also of other traditional risk factors associated with the disease.

Researchers acknowledged several limitations in the study, most importantly the need for survey participants to accurately remember their exercise levels from decades past and make up their own minds what qualified as serious exercise.

Still, they said, the magnitude of the findings, particularly those concerning the transition from frequent exercise to sloth, added significantly to previous findings about how too much exercise can increase overall atrial fibrillation risks.