As the prevalence of obesity increases in the United States, concern over the association
of body weight with excess mortality has also increased.
To estimate deaths associated with underweight (body mass index [BMI] <18.5), overweight
(BMI 25 to <30), and obesity (BMI > or =30) in the United States in 2000.
We estimated relative risks of mortality associated with different levels of BMI (calculated
as weight in kilograms divided by the square of height in meters) from the nationally
representative National Health and Nutrition Examination Survey (NHANES) I (1971-1975)
and NHANES II (1976-1980), with follow-up through 1992, and from NHANES III (1988-1994),
with follow-up through 2000. These relative risks were applied to the distribution
of BMI and other covariates from NHANES 1999-2002 to estimate attributable fractions
and number of excess deaths, adjusted for confounding factors and for effect modification
by age.
Number of excess deaths in 2000 associated with given BMI levels.
Relative to the normal weight category (BMI 18.5 to <25), obesity (BMI > or =30) was
associated with 111,909 excess deaths (95% confidence interval [CI], 53,754-170,064)
and underweight with 33,746 excess deaths (95% CI, 15,726-51,766). Overweight was
not associated with excess mortality (-86,094 deaths; 95% CI, -161,223 to -10,966).
The relative risks of mortality associated with obesity were lower in NHANES II and
NHANES III than in NHANES I.
Underweight and obesity, particularly higher levels of obesity, were associated with
increased mortality relative to the normal weight category. The impact of obesity
on mortality may have decreased over time, perhaps because of improvements in public
health and medical care. These findings are consistent with the increases in life
expectancy in the United States and the declining mortality rates from ischemic heart
disease.