Association of Body Mass Index in Midlife With Morbidity Burden in Older Adulthood and Longevity

Abstract

Importance: Abundant evidence links obesity with adverse health consequences. However, controversies persist regarding whether overweight status compared with normal body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) is associated with longer survival and whether this occurs at the expense of greater long-term morbidity and health care expenditures.

Objective: To examine the association of BMI in midlife with morbidity burden, longevity, and health care expenditures in adults 65 years and older.

Design, setting, and participants: Prospective cohort study at the Chicago Heart Association Detection Project in Industry, with baseline in-person examination between November 1967 and January 1973 linked with Medicare follow-up between January 1985 and December 2015. Participants included 29 621 adults who were at least age 65 years in follow-up and enrolled in Medicare. Data were analyzed from January 2020 to December 2021.

Exposures: Standard BMI categories.

Main outcomes and measures: (1) Morbidity burden at 65 years and older assessed with the Gagne combined comorbidity score (ranging from -2 to 26, with higher score associated with higher mortality), which is a well-validated index based on International Classification of Diseases, Ninth Revision codes for use in administrative data sets; (2) longevity (age at death); and (3) health care costs based on Medicare linkage in older adulthood (aged ≥65 years).

Results: Among 29 621 participants, mean (SD) age was 40 (12) years, 57.1% were men, and 9.1% were Black; 46.0% had normal BMI, 39.6% were overweight, and 11.9% had classes I and II obesity at baseline. Higher cumulative morbidity burden in older adulthood was observed among those who were overweight (7.22 morbidity-years) and those with classes I and II obesity (9.80) compared with those with a normal BMI (6.10) in midlife (P < .001). Mean age at death was similar between those who were overweight (82.1 years [95% CI, 81.9-82.2 years]) and those who had normal BMI (82.3 years [95% CI, 82.1-82.5 years]) but shorter in those who with classes I and II obesity (80.8 years [95% CI, 80.5-81.1 years]). The proportion (SE) of life-years lived in older adulthood with Gagne score of at least 1 was 0.38% (0.00%) in those with a normal BMI, 0.41% (0.00%) in those with overweight, and 0.43% (0.01%) in those with classes I and II obesity. Cumulative median per-person health care costs in older adulthood were significantly higher among overweight participants ($12 390 [95% CI, $10 427 to $14 354]) and those with classes I and II obesity ($23 396 [95% CI, $18 474 to $28 319]) participants compared with those with a normal BMI (P < .001).

Conclusions and relevance: In this cohort study, overweight in midlife, compared with normal BMI, was associated with higher cumulative burden of morbidity and greater proportion of life lived with morbidity in the context of similar longevity. These findings translated to higher total health care expenditures in older adulthood for those who were overweight in midlife.

Figure 1.. Morbidity Scores in Older Age by Body Mass Index (BMI) Category in Midlife

Among those with a respective overall (A) or cardiovascular (B) morbidity score of 0 at age 65 years, annual morbidity score per participant is plotted. For all-cause morbidity, the score represents the Gagne combined comorbidity score (n = 22 058). For cardiovascular morbidity, the score represents a score of cardiovascular conditions (N = 22 763). Each line represents the midlife BMI category (calculated as weight in kilograms divided by height in meters squared), including underweight, normal BMI, overweight, classes I and II obesity, and class III obesity. Morbidity scores were adjusted for age, sex, race and ethnicity, educational level, smoking, hypertension, hyperlipidemia, diabetes, and death during follow-up.

Figure 2.. Total Longevity and Years Lived With All-Cause and Cardiovascular Disease (CVD) Morbidity in Older Age (≥65 Years) by Body Mass Index (BMI) Category in Midlife

Restricted mean survival time analysis provides the mean time in years spent with a Gagne score of 0 compared with scores of 1 to at least 3 (A) as well as without CVD (CVD morbidity score of 0) and with increasing number of cardiovascular conditions with CVD morbidity scores of 1 to at least 3 (B) in older age. For all-cause morbidity, the score represents the Gagne combined comorbidity score (n = 22 058). For CVD morbidity, the score represents a score of cardiovascular conditions (n = 22 763). Body mass index is calculated as weight in kilograms divided by height in meters squared. Total longevity and years lived were adjusted for age, sex, race and ethnicity, educational level, smoking, hypertension, hyperlipidemia, and diabetes.