A higher body mass index (BMI) in midlife is significantly associated with an increased risk for atrial fibrillation (AF) after age 65 years, independent of other midlife risk factors and cardiorespiratory fitness, according to a study in JACC: Advances.

Researchers assessed the association between cardiorespiratory fitness (CRF) and BMI levels and changes in midlife and the risk for AF after the age of 65 years in participants from the Cooper Center Longitudinal Study.

CRF was measured with a symptom-limited maximal treadmill exercise test, and Medicare claims data were collected from the Center for Medicare and Medicaid Services. These data were obtained from 1999 to 2009.

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Cox proportional hazard intensity analysis was used to evaluate the adjusted association between CRF in midlife and risk for AF in older age. BMI-stratified analyses were conducted to assess the association between continuous measures of CRF and risk for AF in patients with and without obesity (BMI ≥30).

The cohort included 18,493 participants (median aged 49.8 years; 79% men; 98% self-reported White; median CRF levels 10.4 metabolic equivalents of task; median BMI, 25.3). After 109,601 person-years of Medicare follow-up, 2558 incident AF events occurred in 9.2% of women and 15.1% of men.

Adjusted analyses showed that higher midlife CRF was associated with a lower risk for AF after adjustment for age, sex, and examination year, although the association was attenuated and no longer significant after additional adjustment for BMI and other risk factors.

A higher BMI was significantly associated with a higher risk for AF independent of baseline CRF and other baseline risk factors (hazard ratio [HR] per 1 kg/m2, 1.05; 95% CI, 1.03-1.06). In stratified analysis based on BMI, the association between continuous measures of CRF and AF risk was not significant in individuals who were not obese (HR per 1 MET, 1.00; 95% CI, 0.98-1.02) and in those with obesity (HR per 1 MET, 0.99; 95% CI, 0.92-1.06) (P-interaction CRF*BMI =.06).

In a subset analysis (N=7,435) with repeat measurement of CRF levels at an average of 2.3±2.8 years from midlife examination, changes in CRF were not associated with the risk for AF in older age (HR per 1 MET increase in CRF, 0.96; 95% CI, 0.90-1.01; P =.12) after adjustment for midlife measures of BMI, CRF, cardiovascular risk factors, and change in BMI. Change in BMI was not significantly associated with AF risk in the most adjusted model (HR per 1 kg/m2 increase in BMI, 1.03; 95% CI, 0.97-1.08; P =.33).

Among several limitations in the observational study, the participants were predominantly White men with high income and education levels. In addition, incident AF was based on Medicare administrative claims data, CRF was not assessed using the gold standard of directly measured peak oxygen uptake in the Cooper Center Longitudinal Study, and echocardiographic data were not available at the baseline visit for most participants.

“These findings suggest that obesity, but not low CRF, in midlife may be an important driver of the higher burden of AF in older individuals,” the investigators concluded.

Disclosure: One of the study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Pandey A, Willis B, Barlow CE, et al. Mid-life cardiorespiratory fitness, obesity, and risk of atrial fibrillation: the Cooper Center longitudinal study. JACC Advances. Published online May 31, 2022. https://doi.org/10.1016/j.jacadv.2022.100040