High-intensity exercise was tied to a reduced risk for atrial fibrillation in postmenopausal women and obese women in particular, researchers said.

According to an analysis of data from the Women’s Health Initiative (WHI), women, ages 50 and up, engaging in 3 to 9 and more than 9 metabolic equivalent-hours (MET-hour) per week of physical activity had a 6% and 10% lower risk of atrial fibrillation, respectively, compared with sedentary participants, according to Marco Perez, MD, of Stanford University in Stanford, Calif., and colleagues.

Higher levels of physical activity reduced the risk conferred by obesity (P=0.033 for interaction), they wrote in the Journal of the American Heart Association.

The group also found that those who did more than 15 MET-hour per week of strenuous activity had a significant 9% reduction in atrial fibrillation risk.

In addition, increased body mass index (BMI) and reduced physical activity were independently associated with higher rates of the heart rhythm disorder after multivariate adjustment, they said.

Obesity is a well recognized risk factor for atrial fibrillation (AF), but Perez told MedPage Today that the impact of physical exercise on atrial fibrillation risk associated with obesity has not been widely studied in higher-risk populations such as postmenopausal women.

“The nature of the association between higher physical activity levels and Afib risk is controversial,” the researcher wrote. “Several studies have reported that strenuous physical activity is associated with increased risk of Afib.” But those studies were done in mostly healthy young athletes or middle-age men with few cardiovascular risk factors who later developed atrial fibrillation, they added.

“If physical activity reduces the risk of Afib conferred by obesity in older women, it may have important implications for the primary prevention of Afib in this vulnerable population,” the researchers wrote.

Study Details

The WHI was a prospective, observation study that included 93,676 postmenopausal women, ages 50 to 79, who were followed for an average 11.5 years. All the women were enrolled between 1994 and 1998.

Current study participants were excluded if they had an atrial fibrillation diagnosis at enrollment, had missing data, or were underweight. The final analysis by Perez and colleagues was done in 81,317 women.

Incident atrial fibrillation was identified using WHI-ascertained hospitalization records and diagnostic codes from Medicare claims. A multivariate Cox hazard regression model adjusted for demographic and clinical risk factors was used to evaluate the interaction between obesity and physical activity, and its association with incident atrial fibrillation.

Physical activity was assessed using self-reported questionnaires completed at study enrollment. The women were asked how frequently they walked outside the home for more than 10 minutes without stopping and engaged in recreational physical activity at levels that increased heart rate and produced sweating.

Strenuous activity was assessed on baseline questionnaires. The women were asked how frequently they engaged in strenuous or very hard exercise resulting in sweating and fast heart beat, such as aerobics, aerobic dancing, jogging, tennis, and swimming laps.

“The frequency, intensity, duration, and type of physical activity were evaluated,” the researchers wrote. “The validity and reproducibility of the WHI physical activity assessment methods have been previously established.”

An estimated MET level was assigned to different speeds of walking and intensities of recreational physical activity using a compendium of physical activity. The midpoint values for ranges of frequency and duration were imputed and multiplied to create an hours-per-week variable. MET levels for each activity were multiplied by hours per week to compute total weekly physical activity for each participant.

The study participants were divided into four categories of physical activity:

0 MET-hour per week (sedentary)
>0-3 MET-hour per week
>3-9 MET-hour per week
>9 MET-hour/week

The first category included women who did not walk outside of their home for more than 10 minutes without stopping at least once weekly, and who “did not engage in recreational physical activity at sufficient intensity to produce increased heart rate or sweating,” the researchers wrote.

Obesity Increased Afib Risk

The average age of the women included in the analysis was 63.4, and 25.1% were obese while 34.5% were overweight. About 4% were diabetic and 42.6% had a history of hypertension.

A total of 13.4% were sedentary while 11.4% performed >0-3 MET-hour per week of physical activity, 22.8% performed >3-9 MET-hour per week, and 52.4% performed >9 MET-hour per week.

“As expected, obesity was associated with an increased prevalence of multiple cardiovascular comorbidities compared to normal-weight participants, including hypertension (38.8% versus 15.6%), diabetes (8.8% versus 1.4%), hyperlipidemia (17.3% versus 11.1%), coronary artery disease (4.2% versus 2.1%), stroke (1.8% versus 1.0%), congestive heart failure (1.2% versus 0.4%), and peripheral artery disease (3.0 versus 1.4%, P

<0.001 for all)," the researchers wrote.

Over an average of 11.5 years of follow-up, 9,792 women included in the analysis developed new-onset atrial fibrillation. After adjustment for several risk predictors including physical activity, higher BMI was independently associated with an increased risk for atrial fibrillation (hazard ratio 1.12 per 5 g/m2 increase, 95% CI 1.10-1.14).

Benefits of Exercise

The analysis of the impact of exercise on atrial fibrillation revealed that compared with sedentary women, women in the highest physical activity group had a significantly lower multivariable-adjusted risk of atrial fibrillation (HR 0.90, 95% CI 0.85-0.96).

Each increase in physical activity level was associated with a lower hazard of incident atrial fibrillation (P>0.001 for linear trend).

The risk of atrial fibrillation conferred by obesity was greater in the sedentary group (HR 1.30, 95% CI 1.17-1.45) than in the most physically active group (HR 1.16, 95% CI 1.08–1.24).

The interaction between obesity and physical activity was significantly associated with incident atrial fibrillation (P=0.033).

Secondary analyses also demonstrated significant interactions between obesity and age (P=0.002) and diabetes (P=0.003) in atrial fibrillation risk.

When the women were divided into categories based on their BMI, ranging from a low of 18.5 kg/m2 to a high of ≥30 kg/m2, and physical activity level and compared with a reference group of normal-weight participants engaging in more than 9 MET-hour per week of physical activity, obese women in the inactive group had the highest risk of atrial fibrillation (HR 1.44, 95%CI 1.34-1.55).

However, obese participants in the highest category of physical activity had a lower atrial fibrillation risk than those in the inactive category (HR 1.17, 95% CI 1.09-1.27).

The difference in atrial fibrillation risk among sedentary versus physically active women was greater in obese participants (HR 1.44 versus HR 1.17) than in overweight (HR 1.11 versus HR 1.03) or normal-weight participants (HR 1.07 versus HR 1.0).

More Intense Workouts?

An analysis of women who engaged in more than 15 MET-hour per week of strenuous physical activity revealed a significantly lower risk of incident atrial fibrillation compared with participants engaging in 0 MET-hour week of strenuous activity (HR 0.91, 95% CI 0.85-0.97).

“The more obese the women were, the more they benefited from regular exercise,” Perez told MedPage Today. “This was a really important finding and it suggests that concerns about strenuous exercise increasing atrial fibrillation risk may not apply to this high-risk population.”

He added that there is still much to learn about the impact of prolonged, extreme, or endurance exercise on other populations. Also, the current results may not apply to premenopausal women and to men.

“I think, in general, the medical community does not really know what the limits of ‘healthy’ exercise are,” Perez pointed out.

From the American Heart Association:

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Primary source: Journal of the American Heart Association
Source reference: Perez M, et al “Obesity, physical activity and their interaction in incident atrial fibrillation in post-menopausal women” J Am Heart Assoc 2014; DOI: 10.1161/​JAHA.114.001127.