You've probably heard that being overweight can increase your risk for diseases such as heart disease and diabetes. Now a new study finds that obesity is strongly linked to death from cancer. The results are published in the New England Journal of Medicine.

Studying the association between BMI and mortality

Researchers from the American Cancer Society studied more than 900,000 American men and women (average age 57) who were cancer-free at the start of the study in 1982. The participants filled out detailed health questionnaires when they enrolled in the study, including information on their height and weight. Using that information, the researchers calculated the participants' body mass index (BMI) and classified them as "normal weight" (BMI 18.5-24.9), "overweight" (BMI 25.0-29.9), or "obese" (BMI 30.0 or above).

They then followed the subjects for 16 years to determine how many had died of cancer and if there was any association between BMI and cancer death. In doing their statistical analyses, the researchers made adjustments for other factors that could influence cancer death risk, such as age, smoking status, diet, alcohol use, and education.

The more weight, the more risk

The heaviest study participants (BMI of 40 or over) were at the greatest risk of dying from any kind of cancer. The heaviest men were 52% more likely to die than normal-weight men, and the heaviest women were 62% more likely to die than their normal-weight counterparts.

From the results, the researchers conclude that as many as 14% of cancer deaths in men and 20% of cancer deaths in women may be attributable to excess weight, and they estimate that 90,000 cancer deaths per year could be prevented if all Americans maintained a healthy weight.

It's important to remember that this study finds only an association between excess weight and cancer death, but it does not prove that obesity causes cancer death. It's unclear what the potential mechanisms of action are behind this association, but it may have something to do with hormonal changes brought about by obesity.

Another good reason to control weight

Because of the large number of people that were followed, this study adds further important evidence of the potential health consequences of obesity. Experts say the best ways to control weight over the long-term are to cut calories and to increase physical activity - in other words, eat less and move more!