Cardiorespiratory Fitness Is Associated with Early Death Among Healthy Young and Middle-aged Baby Boomers and Generation Xers

Background: Increased mortality associated with low cardiorespiratory fitness has shown to take effect during late adulthood in previous generations. A recent rise in early death was observed in the US. We investigated the impact of low cardiorespiratory fitness during young and middle adulthood on premature death in healthy adults from recent generations. Methods: A prospective cohort study of a nationally representative sample of US Baby Boomers and Generation Xers (born 1945-1980). Between 1999-2004, 3242 adults aged 20 to 49 years (weighted N=59 888 450; mean age, 33.8 ± 0.2 years) underwent submaximal treadmill exercise test in the National Health and Nutrition Examination Survey study. Weighted Cox proportional hazards regression were used to evaluate the association of cardiorespiratory fitness with premature death at 65 years or younger Results: During a mean follow-up of 13.8 years, 104 deaths (weighted deaths N =1 326 808) occurred. Low cardiorespiratory fitness was associated with an increased risk of premature death due to all-cause (Hazard ratio [HR], low vs. high: 2.26; 95% CI, 1.10 to 4.64, p for trend=.036) and cancer mortality (HR: low vs. moderate/high: 6.53; 95% CI, 2.38 to 17.9). Further, this association was stronger in adults aged 35 to 49 years at baseline (HR, 4.17 [95% CI, 1.19 to 9.11]). Conclusion: We observed an inverse association between cardiorespiratory fitness during middle adulthood and premature death, which was not detected in proceeding generations. These findings suggested that low cardiorespiratory fitness might be emerging to a new risk factor for early death among US Baby Boomers and Generation Xers.