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Exercise is good for the heart, but too much of a good thing could be bad for healthy adults and patients with cardiovascular disease, according to two observational studies that suggest a J-shaped curve for the dose-response effects of intense physical activity.
Research involving stable chronic heart disease (CHD) patients found daily strenuous exercise to be associated with a more than twofold increased risk for cardiovascular mortality compared with moderate (two- to four-times a week) exercise (2.36, 95% CI 1.05-5.34).
And high-intensity physical activity early in adulthood, but not in middle-age, was found to be associated with an increased risk for atrial fibrillation later in life in a Swedish trial. The study is one of several linking regular strenuous exercise early in life to increased afib risk.
Both studies were published in Heart.
"The literature over the last 50 years overwhelmingly point toward moderate exercise being extremely beneficial from a cardiovascular standpoint, but it is also increasingly clear that extremes on both ends of the exercise spectrum might be detrimental," said Keith Churchwell, MD, who is chief medical officer of the Vanderbilt Heart and Vascular Institute, in Nashville, Tennessee. Churchwell was not involved in either study.
How Much Exercise Do Heart Patients Need?
Widely accepted joint guidelines for patients with stable heart disease, which call for 30 to 60 minutes of moderate intensity aerobic activity, such as brisk walking, 5 to 7 days a week, are based on research showing regular exercise to have a clear positive impact on outcomes in heart patients. But only a few studies have examined the potential benefit of physical activity under real-life conditions, researcher Ute Mons, M.A., of the German Cancer Research Center, Heidelberg, and colleagues, noted.
"These (studies) consistently found the highest risk for adverse outcomes in the most inactive patients, yet the exact dose-response relationship with different levels of physical activity is still unclear," they wrote.
In their study, Mons and colleagues sought to determining the dose-response relationship associated with different levels of physical activity in patients with stable heart disease followed for a decade.
Subjects included a prospective cohort of 1,038 patients in Germany with stable CHD participating in the KAROLA study.
The frequency of strenuous leisure time physical activity was assessed over 10 years of follow-up and multiple Cox proportional hazards regression models were used to assess the association of physical activity level with different outcomes of prognosis (major cardiovascular events, cardiovascular mortality, all-cause mortality), with different sets of adjustments for potential confounders and taking into account time-dependence of frequency of physical activity.
Most Patients Reported Getting Regular Exercise
Health related and sociodemographic data were collected from patients with self-administered standardized questionnaires at rehabilitation. Additional information on medical findings and secondary diagnoses were obtained from hospital medical records.
Patients were assessed at 1, 3, 4.5, 6, 8, and 10 years after discharge from rehabilitation centers to collect lifestyle related, health related and sociodemographic information by means of self-administered standardized questionnaires and physicians were contacted to obtain information on CVD events and the death certificates of deceased patients were reviewed.
The mean age of the study subjects was 61, and around 40% reported engaging in physical activity two to four times a week. Thirty percent of the respondents said they exercised more than this and 30% reported exercising less, with around 10% reporting that they rarely or never engaged in physical activity.
For all outcomes, the highest hazards were consistently found in the least active patient group, with a roughly twofold risk for major cardiovascular events (adjusted model 2.05 [95% CI 1.20-3.51]) and a roughly fourfold risk for all-cause mortality (3.92 [95% CI 2.26-6.79]) in comparison to the reference group of patients who were moderately active (exercised two- to four-times per week).
Strenuous Daily Exercise Linked to Mortality Increase
Patients who reported engaging in strenuous physical activity on a daily basis had a 62% to 78% increased risk for death and a 65% to 2.37% increased risk for CVD death compared with the two- to four-time a week exercising group, in various models.
"When taking time-dependence of physical activity into account, our data indicated reverse J-shaped associations of physical activity level with cardiovascular mortality, with the most frequently active patients also having increased hazards," Mons and colleagues wrote.
A second study by researchers from Stockholm, Sweden's Karolinska Institute assessed the impact of high-intensity physical activity at different ages during adulthood on the development of atrial fibrillation.
Information about physical activity was obtained from 44,410 atrial fibrillation (AF)-free men, aged 45–79 years (mean age=60), who completed a self-administered questionnaire at baseline in 1997. The questionnaire included information on leisure-time exercise and on walking or bicycling throughout their lifetime (at 15, 30 and 50 years of age, and at baseline.
The study participants were followed for a median of 12 years, during which time 4,568 cases of AF were diagnosed.
Men who reported exercising more than 5 hours a week at the age of 30 had a relative risk of developing atrial fibrillation of 1.19 (95% CI 1.05-1.36) compared with those who reported exercising less than 1 hour a week at the same age.
The risk was higher (RR 1.49, 95% CI 1.14-1.95) among the men who exercised >5 h/week at age 30 and quit exercising later in life (<1 h/week at baseline). Walking/bicycling at baseline was inversely associated with risk of AF (RR 0.87, 95% CI 0.77-0.97 for >1 h/day versus almost never) and the association was similar after excluding men with previous coronary heart disease or heart failure at baseline (corresponding RR 0.88, 95% CI 0.77-0.998).
"Our results suggest that a high level of leisure-time exercise (moderate-intensity to high-intensity physical activity) in younger men is associated with an increased risk of AF later in life, and that the increase in risk becomes even higher for those who quit exercising later in life," the researchers wrote. "On the other hand, walking/bicycling (low intensity to moderate-intensity) at an older age seems to reduce the risk of AF, a finding that might be due to positive effects on several traditional cardiovascular risk factors."
Self-Reported Exercise Major Limitation
Both studies showed an increase in mortality associated with intense physical exercise, but both also relied on self-administered questionnaires in which study participants were asked to recall their physical activity years and even decades earlier and were not asked to provide specific information about the exercise they engaged in.
In an accompanying editorial, Eduard Guasch and Lluis Mont of the Thorax Institute in Barcelona noted that this limited the ability of both studies to reliably assess the impact of physical activity on outcomes.
Vanderbilt's Churchwell said the research linking exercise early in life to atrial fibrillation later in life is not yet convincing.
"I would characterize it as relatively weak," he told MedPage Today. "More study is definitely needed to show that exercise at a young age leads to afib later in life."
Churchwell recommends that his heart patients start slow when they begin an exercise regimen, and work up to 40 minutes to an hour of moderate to strenuous exercise 3- to 5 days a week.
"Patients who follow more extreme plans don't tend to stay with their exercise programs," he said. "In terms of improving cardiovascular status, the key is sticking with it."
From the American Heart Association:
- Circ HF: Physical Activity, Sedentary Time, And Risk Of HF
- Guide to the Assessment of Physical Activity: Clinical and Research Applications
- 2013 AHA/ACC Guideline on Lifestyle Management to Reduce Cardiovascular Risk
The study by Mons and colleagues was funded by the German Federal Ministry of Education and Research.
The researchers reported no relevant competing interests.
- Reviewed by Zalman S. Agus, MD Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania and Dorothy Caputo, MA, BSN, RN, Nurse Planner
HeartSource Reference: Mons, U "A reverse J-shaped association of leisure time physical activity with prognosis in patients with stable coronary heart disease" Heart 2014; DOI: 10.1136/heartjnl-2013-305242.
HeartSource Reference: Drca N, et al "Atrial fibrillation is associated with different levels of physical activity levels at different ages in men" Heart 2014; DOI: 10.1136/heartjnl-2013-305304.