Obesity and Mortality

Reference 1 presents the results of a large study involving more than 1 million adults in the U.S., studied for 14 years, during which more than 200,000 deaths occured. The study differentiated between smokers and non-smokers, and people who had a history of illness (heart-disease, cancer, respiratory disease and others). The average age of participants at enrollment was 57.

The primary conclusion from the study is that starting with a BMI of 28 and above, there is an increased risk of mortality. (There is also an indication for an increase in mortality risk for BMI above 25, but it is not statistically significant). For white, non smokers, with no history of disease, the increased risk ratio is roughly

BMI	Risk Ratio	Margin of Error
30-32	1.3	1.2 - 1.4
32 - 35	1.6	1.5 - 1.7
35 - 40	2.0	1.7 - 2.3
> 40	2.1	1.7 - 2.5

These numbers are smaller for black people, and in particular for black women - in fact, their risk ratios are not statistically different from unity (i.e., no increased risk) within the margin of error. The major contributing disease to the increase in mortality in all the populations studied is cardiovascular disease.

Reference 2 presents results of a study specific to the impact of obesity on heart failure. This study finds that for obese people (BMI greater than 30), there is an approximate doubling (risk ratio 2.0, margin of error 1.6 to 2.6) of the risk for heart failure. For people in the "overweight" category, (BMI of 25 to 30), there is a risk increase of 30% (risk ratio of 1.3, margin of error 1.1 to 1.7). The large error associated with this number indicates that it is not totally conclusive that mild obesity (e.g., BMI 25-27) is definitely associated with increased risk. However, the trend towards increased risk with increased BMI is certainly evident.

Another study (reference 3), the Muenster Heart Study, shows that the increase in mortality is due to "traditional" risk factors such as serum total cholesterol, low density lipoprotein (LDL) cholesterol, and blood pressure. In other words, increased BMI raises cholesterol and LDL and blood pressure, leading to the increased mortality.

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Last Modification - August 29, 2008