Many studies support the idea that excess body weight is not only detrimental to optimum health, but also deadly. While research in humans has repeatedly shown that being significantly overweight is correlated with an increased risk of death from cardiovascular disease and death from any cause, it has failed to consistently show a connection between excess weight and cancer mortality.

A study published in the April 24, 2003 New England Journal of Medicine looked at how overweight or obesity might affect mortality from cancer. This study supports a significant relationship between excess weight and increased risk of death from cancer. In fact, the researchers concluded that the current patterns of overweight and obesity could account for 14% of all cancer deaths in men and 20% in women.

About the study

Scientists at the American Cancer Society studied a population of more than 900,000 US adults drawn from the Cancer Prevention Study II—a much larger prospective study that began in 1982. Participants completed questionnaires that included questions about current weight, weight one year previously, and height. Follow-up continued for 16 years, during which 32,303 men and 24,842 women died from cancer.

Using height and weight data from the questionnaires, researchers divided the study participants into groups based on their body mass index (BMI). (BMI is a calculation of weight in kilograms divided by height in meters squared.) BMI values were categorized as follows:

  • 18.5 to 24.9 (considered normal range and used as the reference group)
  • 25.0 to 29.9 (defined as overweight)
  • 30.0 to 34.9 (this value and higher was defined as obesity)
  • 35.0 to 39.9
  • 40.0 and above

Researchers looked at age-adjusted cancer death rates for each BMI group—analyzing how increasing BMI affected risk of death. Because smoking can have such a profound impact on a person's risk of cancer, researchers ran a separate analysis on participants who had never smoked.

The findings

The study found that excess weight has a significant impact on mortality from cancer. Male study participants with BMIs of at least 40 had death rates from all cancers combined that were 52% higher than men with a BMI in the normal range. Women with BMIs of 40 or greater had a 62% higher death rate from all cancers combined than women with a BMI in the normal range.

In addition to all cancers combined, researchers found significant associations between death rates and increasing BMI for several specific cancers (see Table).

Cancers Whose Mortality Rates Increase with Increasing BMI

Men

Women

Esophageal cancer

Colorectal cancer

Stomach cancer

Liver cancer

Colorectal cancer

Gallbladder cancer

Liver cancer

Pancreatic cancer

Gallbladder cancer

Breast cancer

Pancreatic cancer

Cancer of the corpus and uterus

Prostate cancer

Cervical cancer

Kidney cancer

Ovarian cancer

Non-Hodgkin’s lymphoma

Kidney cancer

Multiple myeloma

Non-Hodgkin’s lymphoma

Leukemia

Multiple myeloma

“Other” unspecified cancers


Some of the increased risks were quite striking. For example:

  • The relative risk of death from liver cancer for a man with a BMI of 35 or greater was 4.52 times greater than for a man with a normal BMI.
  • The relative risk of death from uterine cancer for a woman with a BMI of 40 or greater was 6.25 times greater than for a woman with a normal BMI.

Interestingly, lung cancer for both men and women had a significant inverse association between BMI and death rates; as BMI increased, the risk of death from lung cancer decreased.

In participants who never smoked, the association between weight and cancer mortality actually increased for all cancers combined, as well as esophageal cancer, pancreatic cancer, and "other" cancers.

Even though these results are important, the study suffered from some limitations. The researchers relied on self-reported data for weight and height, which tends to slightly overestimate height and underestimate weight. In addition, researchers had no direct measure of total body fat, fat distribution, and lean body mass, all of which could affect the validity of a BMI measurement.

How does this affect you?

The researchers estimate that 90,000 deaths due to cancer could be prevented each year if people could maintain a BMI under 25 throughout life. The large size of this study makes these results all the more compelling.

Excess weight may not just affect mortality from cancer, but also the risk of developing cancer. The International Agency for Research on Cancer (IARC) has found that excess weight can increase risk of developing cancers of the colon, breast (in post-menopausal women), endometrium, kidney, and esophagus. The IARC's conclusions combined with this study's findings strongly support a close connection between body weight and health.

This study adds to the rising tide of evidence linking overweight and obesity with serious health implications. For many who need to, losing weight is an enormously difficult challenge. The payoffs, however, can be equally enormous.