Cardiorespiratory fitness and adiposity as mortality predictors in older adults

Abstract

Context: Although levels of physical activity and aerobic capacity decline with age and the prevalence of obesity tends to increase with age, the independent and joint associations among fitness, adiposity, and mortality in older adults have not been adequately examined.

Objective: To determine the association among cardiorespiratory fitness ("fitness"), adiposity, and mortality in older adults.

Design, setting, and patients: Cohort of 2603 adults aged 60 years or older (mean age, 64.4 [SD, 4.8] years; 19.8% women) enrolled in the Aerobics Center Longitudinal Study who completed a baseline health examination during 1979-2001. Fitness was assessed by a maximal exercise test, and adiposity was assessed by body mass index (BMI), waist circumference, and percent body fat. Low fitness was defined as the lowest fifth of the sex-specific distribution of maximal treadmill exercise test duration. The distributions of BMI, waist circumference, and percent body fat were grouped for analysis according to clinical guidelines.

Main outcome measure: All-cause mortality through December 31, 2003.

Results: There were 450 deaths during a mean follow-up of 12 years and 31 236 person-years of exposure. Death rates per 1000 person-years, adjusted for age, sex, and examination year were 13.9, 13.3, 18.3, and 31.8 across BMI groups of 18.5-24.9, 25.0-29.9, 30.0-34.9, and > or =35.0, respectively (P = .01 for trend); 13.3 and 18.2 for normal and high waist circumference (> or =88 cm in women; > or =102 cm in men) (P = .004); 13.7 and 14.6 for normal and high percent body fat (> or =30% in women; > or =25% in men) (P = .51); and 32.6, 16.6, 12.8, 12.3, and 8.1 across incremental fifths of fitness (P < .001 for trend). The association between waist circumference and mortality persisted after further adjustment for smoking, baseline health status, and BMI (P = .02) but not after additional adjustment for fitness (P = .86). Fitness predicted mortality risk after further adjustment for smoking, baseline health, and either BMI, waist circumference, or percent body fat (P < .001 for trend).

Conclusions: In this study population, fitness was a significant mortality predictor in older adults, independent of overall or abdominal adiposity. Clinicians should consider the importance of preserving functional capacity by recommending regular physical activity for older individuals, normal-weight and overweight alike.