Abstract and Introduction
Abstract
Background: Published studies about the association of obesity with mortality have used body mass index (BMI) data collected more than 10 years ago, potentially limiting their current applicability, particularly given evidence of a secular decline in obesity-related mortality. The objective of this study was to examine the association between BMI and mortality in a representative, contemporary United States sample.
Methods: This was a population-based observational study of data from 50,994 adults aged 18 to 90 years who responded to the 2000 to 2005 Medical Expenditures Panel Surveys. Cox regression analyses were employed to model survival during up to 6 years of follow-up (ascertained via National Death Index linkage) by self-reported BMI category (underweight, <20 kg/m; normal weight, 20-<25 [reference]; overweight, 25-<30; obese, 30-<35; severely obese, ≥35), without and with adjustment for diabetes and hypertension. Survival by BMI category also was modeled for diabetic and hypertensive individuals. All models were adjusted for sociodemographics, smoking, and Medical Expenditures Panel Surveys response year.
Results: In analyses not adjusted for diabetes or hypertension, only severe obesity was associated with mortality (adjusted hazard ratio, 1.26; 95% confidence interval, 1.00–1.59). After adjusting for diabetes and hypertension, severe obesity was no longer associated with mortality, and milder obesity (BMI 30-<35) was associated with decreased mortality (adjusted hazard ratio, 0.81; 95% confidence interval, 0.68–0.97). There was a significant interaction between diabetes (but not hypertension) and BMI (F [4, 235] = 2.71; P = .03), such that the mortality risk of diabetes was lower among mildly and severely obese persons than among those in lower BMI categories.
Conclusions: Obesity-associated mortality risk was lower than estimated in studies employing older BMI data. Only severe obesity (but not milder obesity or overweight) was associated with increased mortality, an association accounted for by coexisting diabetes and hypertension. Mortality in diabetes was lower among obese versus normal weight individuals.
Introduction
Overweight and obesity have increased dramatically, with adverse public health implications. Above-normal body mass index (BMI) is associated with decreased functional ability and health status and increased risk of chronic conditions such as diabetes and hypertension, which often cause further decrements in health. However, the contemporary relationship between BMI and mortality, and how BMI interacts with diabetes and hypertension to influence mortality, are unclear.
Studies conducted more than 30 years ago suggested incrementally rising mortality risk with each increase in BMI category above normal, prompting predictions of reduced life expectancy because of burgeoning obesity. However, subsequent studies of BMI data collected 10 to 30 years ago have found consistently increased mortality risk only among severely obese persons (BMI ≥35 kg/m), with mixed findings among overweight (BMI 25.0–29.9 kg/m) and more mildly obese (BMI 30.0–34.9 kg/m) persons. Collectively, these findings suggest a secular decline in the mortality risk of those with above-normal BMI.
Secular trends in population obesity suggest the need for studies employing more recently collected BMI data. Examining the current relationships among obesity, its principal morbidities (hypertension and diabetes), and mortality would help assess whether these relationships have changed. Elucidating current relationships among diabetes, BMI, and mortality is particularly relevant given the adoption in the 1990s of a lower threshold for diagnosing diabetes. Using national data from the 2000 to 2005 Medical Expenditures Panel Surveys (MEPSs), linked with the National Death Index (NDI) through 2006, this study examined the association between self-reported BMI and all-cause mortality among US adults and the degree to which BMI moderates mortality risk in diabetes and hypertension during up to 6 years of follow-up.