Obesity is known to be associated with many potentially life threatening diseases such as heart disease, diabetes, and some forms of cancer. According to most scientific studies, there is an inverse linear relationship between life expectancy and body mass index (BMI). Those who are considered obese (a BMI greater than 30) can expect to live on average 6 to 7 years less than people in the normal weight range (BMI less than 25).
One study, published in the journal Annals of Internal Medicine, looked at the impact obesity has on remaining life expectancy at 40 years of age. The study involved 3,457 individuals who were divided into three groups: normal weight (BMI < 25), overweight (BMI between 25 and 30), and obese (BMI > 30).
During the forty year study period, 1,647 (47.6%) of the participants died. The researchers found that individuals in the obese group died on average 6 to 7 years earlier than the normal weight group regardless of gender or smoking status. In the overweight group, life expectancy was reduced by 3 years for non-smokers, and by 1 year for male non-smokers. Overweight female smokers did not have a significantly reduced life expectancy compared to female smokers of a normal weight.
The full results of the study are presented in the graph below.
A second study, published in the Journal of the American Medical Association in 2003, looked at the impact obesity has on life expectancy at different stages of life. The study found that obesity in younger people, particularly those under the age of 30, appears to have the greatest effect on life expectancy. On the other hand, obesity had little effect on life expectancy in adults aged over 60 years.
Cardiovascular diseases such as heart disease and strokes are the major cause of premature death in obese individuals. Almost 40% of heart attacks in people under the age of 50 are thought to be caused by obesity. Obesity is strongly correlated with several heart disease risk factors including high blood pressure, poor physical fitness, high blood lipid levels, and diabetes.
Almost 65% of Americans are overweight and 30% are obese. In 1980, overweight and obesity rates were just half of what they are today. Life expectancy at birth in the United States is currently 74 and 80 years for men and women respectively. Life expectancies have plateaued in the western world in the last decade and it is thought the huge increase in obesity rates is partly responsible for this. If overweight and obesity rates in the United States had remained constant since 1980, it is estimated that life expectancy would be almost three years greater than what it is today.