Higher cardiorespiratory fitness levels attenuate but do not negate the heightened risk of sudden cardiac death due to obesity: A prospective cohort study.

Background: Higher levels of CRF have been demonstrated to attenuate or negate the adverse cardiovascular impacts of other risk factors. We aimed to assess the interplay between body mass index (BMI), CRF and sudden cardiac death (SCD) risk. Methods: Body mass index was calculated based on guideline recommendations and CRF assessed using a respiratory gas exchange analyzer during clinical exercise testing at baseline in 2308 men aged 42-61 years of age. Cox regression analysis was used to estimate hazard ratios (HRs) with 95 % confidence intervals (CIs) for SCD. Results: During a median follow-up of 28.1 years, 264 SCDs occurred. Comparing obese vs normal weight category, the multivariable-adjusted HR (95 % CI) for SCD was 1.86 (1.28-2.71). Comparing low vs high CRF levels, the corresponding adjusted HR (95 % CI) for SCD was 1.99 (1.38-2.87). The HRs persisted on mutual adjustment for each exposure. Compared with non-obese and medium-high CRF, obese individuals with low CRF levels had the greatest risk of SCD (HR = 2.90, 95 % CI, 1.98-4.25), which was attenuated but persisted in obese individuals with medium-high CRF levels (HR = 2.02, 95 % CI, 1.08-3.78). Conclusions: There is an interplay between BMI, CRF and SCD risk. Higher CRF levels may attenuate the risk associated with obesity.