Obesity Linked to Increased Cancer Risk
WEDNESDAY Oct. 31, 2007 -- Weight management, exercise and proper nutrition are key to reducing your risk of cancer. And the earlier in life you adopt these practices, the better off you'll be, a new study suggests.
Factors such as birth weight, childbearing, breast-feeding, and adult height and weight also influence cancer risk, according to the report released Wednesday by the American Institute for Cancer Research and the Britain-based World Cancer Research Fund. Understanding how these factors affect cancer risk, and how to put this information to use to prevent the disease, offer promising new directions for cancer research, the study authors said.
"We need to think about cancer as the product of many long-term influences, not as something that 'just happens,' " Dr. Walter J. Willett said in a prepared statement. Willett, a professor of epidemiology and nutrition at the Harvard School of Public Health, was one of 21 authors of the report, Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective.
"Examining the causes of cancer this way, across the entire lifetime, is called the life course approach," he added.
The report, an analysis by scientists from around the world of more than 7,000 studies, offers 10 recommendations to help prevent cancer. They include staying lean, getting at least 30 minutes of exercise daily, limiting your intake of red meat and alcohol, and avoiding processed meats.
"These findings are right on," said Colleen Doyle, director of nutrition and physical activity at the American Cancer Society. "They are consistent with our own nutrition and physical activity guidelines. They clearly put the emphasis where the emphasis needs to be, and that's on controlling your weight."
"This is a good-news report," added Karen Collins, a nutrition adviser at the American Institute for Cancer Research. "If we are watching our weight, working regular physical activity into our daily life and eating a healthy balance of foods, we could prevent a third of cancers," she said. "Extra weight is not dead weight," she said. "It's an active metabolic tissue that produces substances that promote the development of cancer."
"People should take this message to be empowering," Collins said.
The analysis of the studies found a definite link between excess fat and cancers of the esophagus, pancreas, colon and rectum, endometrium, kidney as well as breast cancer in postmenopausal women.
The risk from excess weight begins at birth, according to the report. The reason for the link between birth weight and breast cancer has to do with body fat. Excess body fat influences the body's hormones, and these changes can make it more likely for cells to undergo the kind of abnormal growth that leads to cancer, the researchers said.
In addition, overweight girls can start menstruating at an earlier age. So, over their lifetime, they will have more menstrual cycles. This extended exposure to estrogen is associated with increased risk for premenopausal breast cancer, the report found.
Not smoking is the most important thing one can do to reduce the risk of cancer, Doyle said. But, she added, "there are estimates that obesity will overtake smoking as the leading preventable cause of death.
"It's great to see another report that emphasizes being active, watching your weight and eating a healthy diet are not only going to help you reduce your risk of cancer but heart disease and diabetes as well," Doyle said.
The report also found that breast-feeding can lower a mother's risk for developing breast cancer. In addition, breast-fed infants have a lower risk of becoming overweight or obese, and this means a lower risk of developing cancer.
"The evidence is uniformly strong on breast-feeding, and the fact that it offers cancer protection to both mothers and their children is why we made breast-feeding one of our 10 Recommendations to Prevent Cancer," Willett said.
In addition, tall people seem to have a higher risk of colorectal and postmenopausal breast cancer, according to the report.
"We found that tallness is also probably linked to increased risk for ovarian, pancreatic and premenopausal cancer as well," Willett said. Although the association between height and cancer is convincing, tall people are not destined to get cancer, he added.
Willett noted that being at increased risk is not a guarantee that you are going to develop cancer. "Risk isn't fate," he said. "The evidence clearly shows that risk can be changed.
"We wanted to point these emerging links out, because we now believe them to be more important than the scientific community, much less the public, has yet realized," Willett added. "Whether or not we get cancer has to do with our genes and with the choices we make everyday. Our cancer risk is also influenced by our whole accumulated life experience, from conception onwards."
Body weight and composition is a big factor, one expert said.
"This report really reinforces the connection between being overweight or obese and the increased risk of many, if not all, cancers," said Carolyn Lammersfeld, the national director of nutrition at Cancer Treatment Centers of America. "The majority of Americans are not aware of that connection. They are more concerned with pesticides and environmental contaminants, but obesity is a much greater risk factor," she said.
But risks can be minimized, she added. "If you don't have cancer, it's never too late to try to do what you can to lower your risk," Lammersfeld said. "In addition, cancer survivors should follow the diet and weight recommendations to prevent a return of cancer."
The report said that people should not use dietary supplements to try to offset cancer risk -- something Lammersfeld agreed with. "You can't fix a crappy diet with supplements," she said.
To read the full report, visit the American Institute for Cancer Research.
Posted: October 2007