Effect of age on excess mortality in obesity

Context The effect of age on excess mortality from all causes associated with obesity is controversial. Few studies have investigated the association between body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters), age, and mortality, with sufficient numbers of subjects at all levels of obesity. Objective To assess the effect of age on the excess mortality associated with all degrees of obesity. Design Prospective cohort study. Setting and Participants A total of 6193 obese patients with mean (SD) BMI of 36.6 (6.1) kg/m(2) and mean (SD) age of 40.4 (12.9) years who had been referred to the obesity clinic of Heinrich-Heine University, Dusseldorf, Germany, between 1961 and 1994. Median follow-up time was 14.8 years. Main Outcome Measure All-cause mortality through 1994 among 6053 patients for whom follow-up data were available (1028 deaths) analyzed as standardized mortality ratios (SMRs) using the male-female population of the geographic region (North Rhine Westphalia) as reference. Results The cohort was grouped into approximate quartiles according to age (18-29, 30-39, 40-49, and 50-74 years) and BMI (25 to <32, 32 to <36, 36 to <40, and greater than or equal to 40 kg/m(2)) at baseline. The SMRs showed a significant excess mortality with an SMR for men of 1.67 (95% confidence interval, 1.51-1.85; P<.001) and an SMR for women of 1.45 (95% confidence interval, 1.34-1.57; P<.001), The excess mortality associated with obesity declined with age. For men, the SMRs of the 4 age groups were 2.46, 2.30, 1.99, and 1.31, respectively; for women, they were 1.81, 2.10, 1.70, and 1.26, respectively (Poisson trend test, P<.001). The SMRs increased with BMI but, within each BMI group, the SMRs decreased with age. The lowest SMRs (for men, 1.01; for women, 0.91) were obtained for patients older than 50 years with BMIs of 25 to less than 32 kg/m(2). Thus, older men and women at a BMI range of 25 to less than 32 kg/m(2) had no excess mortality. The highest SMRs (for men, 4.22; for women, 3.79) were calculated for the patients aged 18 to 29 years with a BMI of 40 kg/m(2) or higher. Conclusions In this large cohort of obese persons, risk of death increased with body weight, but obesity-related excess mortality declined with age at all levels of obesity.