Incidence of AF rises sharply with age, and most cases in the population occur after age 65. While vigorous exertion and endurance training have been reported as risk factors for AF in younger and middle-aged populations, this is the first study to focus on older adults and to evaluate prospectively the relationships of light to moderate habitual physical activity with incidence of AF. Greater leisure-time activity and walking were associated with graded lower incidence of AF, with progressively lower risk as both leisure-time activity and distances and paces of walking increased. Conversely, intensity of exercise had a U-shaped relationship with AF, with lower risk among individuals exercising with moderate, but not high, intensity.
Physical activity and exercise may have both acute (during a bout) and chronic (related to habitual activity) physiologic effects. For example, whereas the risk of sudden cardiac death may be transiently increased during vigorous exercise, habitual physical activity is associated with an overall decreased risk of sudden cardiac death.21–23
Higher risk of AF has been reported in case series and retrospective studies of younger athletes and middle-aged adults with high intensity or endurance exercise,5–10
which if causal could reflect relatively transient higher risk during/immediately following a bout of exercise, and/or more chronic left ventricular structural changes related to prolonged high intensity training.24, 25
In a retrospective study, 262 military veterans likely to have undergone long-term vigorous exercise had higher prevalence of AF compared with population volunteers (6.1% vs. 4.6%), largely due to greater lone AF (which offset lower prevalence of risk factor-related AF).5
Among 137 patients undergoing ablation of isthmus-dependent atrial flutter, the 31 patients performing semi-competitive endurance sports had more frequent post-ablation AF at 1 year (81% vs. 48%; multivariable HR=1.81, p=0.02), compared to those not undertaking such endurance sports.9
In a retrospective study, 70 middle-aged patients with lone AF seen at an arrhythmia clinic were more likely to have engaged in long-term sports training (46%) than the general population (15%)7
and more likely to report current sports practice (31%) compared with population controls (14%).10
Thus, case series and retrospective studies suggest that long-term endurance athletes have higher risk of AF, particularly lone AF, than the general population. Conversely, such analyses may be limited by selection bias and recall bias. In a Danish cohort of middle-aged adults, no significant associations were seen between bouts of strenuous activity in the workplace and risk of AF,26
but physical activity habits outside of work were not assessed.
In the present work, we examined prospectively the risk of AF associated with usual, habitual, or chronic levels of light to moderate physical activity. Thus, the observed risk estimates may in essence reflect the balance between long-term benefits associated with habitual activity and (potentially) higher acute risk “during” activity. In contrast to prior retrospective reports and case series,5–10
high intensity exercise was not associated with higher AF risk; this could relate to relatively lower maximal intensity of exercise in these older adults compared with younger adults, differences in pathoetiology of AF later in life, and/or design differences (e.g., prospective vs. retrospective investigation). However, high intensity exercise was also not associated with lower AF risk, suggesting an overall net neutral association of high intensity exercise with AF incidence in older adults. In comparison, moderate physical activities, such as greater leisure-time activity, distances and paces of walking, and moderate intensity exercise, were associated with significantly lower risk. These results suggest that long-term benefits for AF risk of light to moderate physical activities in older adults outweigh any potential higher risks of AF associated with the acute activity or exercise.
Moderate physical activity has several physiologic benefits that could reduce the incidence of AF in older adults.27–30
Physical activity induces and maintains weight loss; additional effects on maintenance of lean body mass may also be particularly relevant later in life. Physical activity lowers resting heart rate and blood pressure, improves fasting and postprandial glucose control, and improves serum lipoprotein levels and mental well-being. Physical activity may also improve endothelial function, lower systemic inflammation, and facilitate quitting smoking. Each of these factors are risks for AF. When we adjusted for differences in left ventricular mass and metabolic risk factors such as body mass index, blood pressure, glucose, cholesterol, and C-reactive protein levels, the relationships of the physical activity measures and incident AF were partly attenuated, suggesting that part of the observed lower risk may be mediated by effects of activity on these risk factors. Associations of physical activity with lower AF risk also appeared potentially mediated, in part, by lower risk of preceding MI or CHF.
In considering relationships between physical activity and incident AF, potential confounding by underlying comorbidity must be carefully assessed. Some individuals may have comorbidities that both limit their physical activity and increase risk of AF, which would cause physical activity to appear more protective than the true effect. Conversely, other individuals may increase their physical activity in response to diagnosis of a condition that also increases risk of AF (confounding by indication), which would cause physical activity to appear less protective than the true effect. Multivariable adjustments are one method to decrease such confounding. We also used restriction and stratification to assess such potential confounding. The findings did not appear to be attributable to confounding by presence of comorbid conditions, such as chronic pulmonary disease, preexisting CHD, or preexisting cardiovascular disease. Notably, the relationships of most potential confounders were similar or even more prominent for exercise intensity than for leisure-time activity (), but multivariable-adjusted analyses revealed different relationships of exercise intensity (U-shaped risk) vs. leisure-time activity (graded lower risk) with incident AF, suggesting that confounding alone would not fully account for the observed relationships.
Our analysis has several strengths. The prospective assessment of physical activity and other covariates reduces potential bias from recall differences. The cohort design minimizes selection bias (i.e., the non-cases represent the true population from which the cases arose). Standardized assessment of a wide variety of participant characteristics increases the capacity to adjust for confounding. Close follow-up, annual ECGs, and review of all hospitalizations reduce potential for missed or misclassified outcomes. The use of repeated assessments of physical activity and other risk factors over time reduces misclassification due to changes in activity and assesses long-term effects. The large number of events provides ample statistical power. The population-based recruitment strategy enhances generalizability.
Potential limitations are also evident. Physical activity was self-reported and assessed average activity in the prior two weeks at each visit, and some misclassification of the true activity of each individual is likely (although cumulative averaging over time reduces such error). Cases of asymptomatic paroxysmal AF may have been missed, reducing power to detect associations. The possibility of residual confounding due to unmeasured or imprecisely measured factors cannot be excluded. On the other hand, these findings are consistent with observational studies showing lower incidence of CHD and diabetes with greater physical activity; the latter relationship has been confirmed in randomized controlled trials.31,32
The associations were observed in older adults participating in a cohort study and may not be generalizable to younger individuals.
Overall, 1 in 5 of these older U.S. adults developed AF during 12 years of follow-up. Our findings suggest that moderate physical activity may meaningfully reduce this risk, and that up to one-quarter of new cases of AF in older adults may be attributable to absence of moderate leisure-time activity and regular walking at a moderate distance and pace. These results suggest that these easily achievable lifestyle habits should be further evaluated as potential preventive measures to reduce the incidence of AF in the particularly high-risk and growing population of older adults.