WEDNESDAY, Nov. 7, 2007 (HealthDay News) -- A study of more than 1 million British women finds that overweight or obesity is to blame for about 5 percent of all cancer cases.
That's about 6,000 out of the 120,000 cancers affecting British women each year.
The study, by researchers from the University of Oxford, found that overweight and obese women are at higher risk of developing and dying from cancer, including breast cancer in postmenopausal women, colon cancer in premenopausal women, and pancreatic and kidney cancer generally.
"Among middle-aged and older women in the U.K., around 5 percent of all new cancers each year are actually due to overweight or obesity," estimates lead researcher Gillian Reeves, a statistical epidemiologist at Oxford's Cancer Research UK Epidemiology Unit.
"It is important that women be aware that being overweight carries some excess risk of certain types of cancers," Reeves said. "This is something they need to take into consideration alongside what we know are very strong adverse effects of being overweight on diseases like diabetes and heart disease."
In the study, Reeves and colleagues looked at the relationship between body-mass index (BMI), and cancer in 1.2 million British women aged 50 to 64, who took part in the Million Women Study. In the U.K., about 23 percent of all women are obese and 34 percent are overweight, according to national statistics.
During 5.4 years of follow-up, the researchers found more than 45,000 new cancers and more than 17,200 deaths from cancer. Being overweight or obese was linked to an increased incidence for all cancers combined, according to the report in the Nov. 7 online edition of the British Medical Journal.
Being overweight or obese can significantly increase the risk of some cancers in women, Reeves' group found.
Specifically, obese and overweight women were twice as likely to develop endometrial cancer and cancer of the esophagus compared with normal weight women. In addition, overweight and obese women had a 53 percent greater risk of kidney cancer, a 50 percent greater risk of multiple myeloma and a 24 percent greater risk of pancreatic cancer compared with their normal weight counterparts.
Obesity's link to cancer risk appeared to be associated with menopause for certain tumor types. For example, postmenopausal overweight or obese women had a 40 percent increased risk of developing breast cancer, while premenopausal and overweight women had a 61 percent increased risk of developing colorectal cancer, the researchers found.
The rise in cancer risk for overweight and obese women mirrored findings reported last Wednesday by the American Institute for Cancer Research and the Britain-based World Cancer Research Fund.
In that review of 7,000 studies, researchers found a definite link between excess fat and cancers of the esophagus, pancreas, colon and rectum, endometrium and kidneys in all women, as well as breast cancer in postmenopausal women.
Reeves' team also found that, in general, overweight and obese women were more likely to die from cancer once they developed the illness compared to slimmer women. The obesity-linked increase in the rate of cancer death was similar to the increase in cancer risk, the researchers reported.
One expert said the findings highlight another reason to stay slim.
"This study adds to the considerable body of evidence that shows the relationship between overweight obesity and cancer risk," said Eugenia E. Calle, managing director of analytic epidemiology at the American Cancer Society and author of an accompanying journal editorial.
To reduce their risk of cancer, women need to stay lean, Calle said. "Women should not gain weight in adulthood and maintain a weight that puts you on the lean end of normal weight," she said. This is also a benefit in preventing heart disease, diabetes and other medical problems, and maintaining a good quality of life, she added.
In related news, a study in the Nov. 7 issue of the Journal of the American Medical Association found obesity to be associated with 11 percent of deaths from cancers that are already considered to be obesity-related. The trend was not seen for non-obesity-related cancers, however.
"We estimate about 5 percent of all cancer deaths are associated with obesity," said the lead author of that study, Katherine M. Flegal, of the U.S. National Center for Health Statistics. "That ranges from -0.2 to 7.9 percent, so there is not much of a difference between the two studies."
For more on cancer in women, visit the U.S. National Cancer Institute.