Body Mass Index and Mortality in a Very Large Cohort: Is It Really Healthier to Be Overweight?

Controversy persists about optimal body weight. Many experts define "normal" (healthy) body mass index (BMI) as 18.5 to 24.9 kg/m², 25 to 29.9 kg/m² as overweight, and 30 kg/m² or greater as obese. Obesity is subdivided into 30 to 34.9 kg/m² (Grade 1), 35 to 39.9 kg/m² (Grade 2), and 40 kg/m² and above (Grade 3). Studies consistently show higher mortality for underweight and Grade 2 or 3 obesity, but results conflict for the overweight category and Grade 1 obesity.

To study 30-year risk of death related to baseline BMI.

Retrospective cohort study in a multiracial population of 273,843 persons using logistic regression with 7 covariates (sex, age, race-ethnicity, education, marital status, smoking, alcohol intake).

Mortality risk by baseline BMI.

With average follow-up exceeding 30 years, there were 103,218 deaths: 41,215 attributed to cardiovascular causes and 62,003 to noncardiovascular causes. Odds ratios (and 95% confidence intervals) for all deaths in BMI categories, with a BMI of 18.5 to 24.9 kg/m² as the referent, were BMI below 18.5 kg/m² = 1.1 (1.0-2.0), BMI 25 to 29 kg/m² = 1.1 (1.1-1.2), BMI 30 to 34 kg/m² = 1.5 (1.4-1.5), BMI 35 to 39 kg/m² = 2.1 (1.9-2.3), and BMI 40 kg/m² or higher = 2.7 (2.4-3.0). Disparities existed regarding age, race/ethnicity, cause of death, and interval to death.

Compared with persons with BMI defined as normal, persons who were underweight, overweight, and obese were at increased risk of death over 30 years.