Body mass index and future healthcare costs: a retrospective cohort study.

OBJECTIVE: To assess the relationship between body mass index (BMI) and future healthcare costs. RESEARCH METHODS AND PROCEDURES: We undertook a retrospective cohort study of the relationship between obesity and future healthcare costs at Kaiser Permanente Northwest Division, a large health maintenance organization in Portland, Oregon. Study subjects (n = 1286) consisted of persons who responded to a 1990 health survey that was mailed to a random sample of adult Kaiser Permanente Northwest Division members who were 35 to 64 years of age; had a BMI > or = 20 kg/m(2) (based on self-reported height and weight); did not smoke cigarettes; and did not have a history of coronary heart disease, stroke, human immunodeficiency virus, or cancer. Subjects were stratified according to their BMI in 1990 (20 to 24.9, 25 to 29.9, and > or = 30 kg/m(2); n = 545, 474, and 367, respectively). We then tallied their costs (in 1998 US dollars) for all inpatient care, outpatient services, and prescription drugs over a 9-year period (1990 through 1998). RESULTS: For persons with BMIs of 20 to 24.9 kg/m(2), mean (+/-SE) annual costs of prescription drugs, outpatient services, inpatient care, and all medical care averaged $261 (+/-18), $848 (+/-59), $532 (+/-85), and $1631 (+/-120), respectively, over the study period. Cost ratios (95% confidence intervals) for persons with BMIs of 25 to 29.9 kg/m(2) and > or = 30 kg/m(2), respectively, were 1.37 (1.12 to 1.66) and 2.05 (1.62 to 2.55) for prescription drugs, 0.96 (0.83 to 1.13) and 1.14 (0.97 to 1.37) for outpatient services, 1.20 (0.81 to 1.86) and 1.38 (0.91 to 2.14) for inpatient care, and 1.10 (0.91 to 1.35) and 1.36 (1.11 to 1.68) for all medical care. DISCUSSION: Future healthcare costs are higher for persons who are overweight, especially those with BMIs > or = 30 kg/m(2).