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Obesity in adults: Health hazards

George A Bray, MD
Section Editor
F Xavier Pi-Sunyer, MD, MPH
Deputy Editor
Kathryn A Martin, MD


The morbidity and mortality associated with being overweight or obese have been known to the medical profession for more than 2000 years [1]. Overweight refers to a weight above the “normal” range. This is determined by calculating the body mass index (BMI, defined as the weight in kilograms divided by height in meters squared). Overweight is defined as a BMI of 25 to 29.9 kg/m2, obesity as a BMI of >30 kg/m2. Severe obesity is defined as a BMI >40 kg/m2 (or ≥35 kg/m2 in the presence of comorbidities).

The health hazards associated with obesity are reviewed here. The prevalence of and therapy for obesity, and the evaluation of the overweight patient are discussed elsewhere. (See "Obesity in adults: Overview of management" and "Obesity in adults: Prevalence, screening, and evaluation".)


Effect of BMI on mortality — In general, greater body mass index (BMI) is associated with increased rate of death from all causes and from cardiovascular disease (CVD) (figure 1). This is particularly true for those with severe obesity [2]. Obesity is typically defined on the basis of the BMI, which is measured using a patient's weight (in kg) divided by height (in m2).

A number of large epidemiologic studies have evaluated the relationship between obesity and mortality [2-13]. As an example, a meta-analysis of 97 studies (2.88 million individuals) showed that, compared with normal weight, being obese was associated with higher all-cause mortality (hazard ratio [HR] 1.18, 95% CI 1.12-1.25 for all grades of obesity combined) [14]. Estimates for the annual number of excess deaths attributable to obesity in the United States are variable and range from 111,909 to 365,000 [15,16].

Being overweight also appears to be associated with decreased survival in some [5,10,17], but not all [12,14,18], studies. As examples:


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Literature review current through: Jan 2016. | This topic last updated: Jan 2, 2016.
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