(HealthDay)—A new report reveals that excess weight raises the risk of yet another kind of cancer, with the latest results linking levels of body fat to ovarian tumors.
The chances for developing many cancers—such as postmenopausal breast, colorectal, endometrial, esophageal, kidney, gallbladder and pancreatic cancers—are known to increase with a person's weight, but the evidence for any such link to ovarian cancer has been inconclusive until now, the report authors said.
"We estimated a 6 percent increase in [ovarian cancer] risk per five [points] increase in body-mass index," said report author Dr. Elisa Bandera, an associate professor of epidemiology at the Rutgers Cancer Institute of New Jersey, in New Brunswick. Bandera said the average woman's lifetime risk of ovarian cancer is 1.4 percent.
Body-mass index (BMI) is a rough estimate of a person's body fat based on weight and height. A BMI between 18.5 and 24.9 is considered normal. Between 25 and 29.9 is overweight, and 30 and over is considered obese, according to the U.S. Centers for Disease Control and Prevention.
Almost 600,000 people develop one of the eight cancers linked to overweight and obesity in the United States each year, according to the report compiled by the American Institute for Cancer Research and the World Cancer Research Foundation. If everyone were at a healthy weight, about one in five of those cancers—or 120,000 cases of cancer a year—could be prevented, according to the report.
"We know that obesity affects hormones known to affect the cancer process," Bandera said. "It also leads to insulin resistance and [high levels of insulin], as well as a chronic systemic inflammation. Inflammation, in particular, has been a major factor implicated in ovarian cancer development and is also associated with poorer survival."
Registered dietician Samantha Heller said she wasn't surprised by the report's findings.
"Research suggests that up to 90 percent to 95 percent of cancers may be preventable with diet and lifestyle," said Heller, the clinical nutrition coordinator at the Center for Cancer Care at Griffin Hospital, in Derby, Conn. "Of those, as many as 30 percent to 35 percent are linked to diet."
"Contrary to popular belief, fat cells are not the inert compounds we once thought," Heller said. "They are biologically very active cells that produce both anti-inflammatory and inflammatory compounds, as well as hormones and other chemicals."
"An excess of fat cells—if someone is overweight or obese—appears to knock off the body's delicate balance of health," Heller said. "This can lead to inflammation and hormonal imbalances, and can promote the growth of cancer cells."
The current report is part of an ongoing project. The last report was published in 2007, Bandera said.
Overall, the report included 25 population-based studies examining how diet, weight and physical activity might affect the risk of ovarian cancer. Ovarian cancer is the fifth leading cause of cancer deaths in the United States. A major reason for that is that ovarian cancer often isn't diagnosed until it's in the later stages.
Bandera and her colleagues concluded that body fat is likely a contributing factor to the development of ovarian cancer. The risk is greatest for those with a BMI over 30, she added.
Although the study found an association between body fat and ovarian cancer risk, it did not establish a cause-and-effect link.
The report also found that height is a factor in the development of ovarian cancer, with taller women at higher risk. The reason height is linked to ovarian cancer is unclear, Bandera said, although genetic factors and early growth rates might play a role.
"What this means for cancer prevention is that prevention efforts need to target the life course, not just adulthood, and families, not just individuals," Bandera said.
The researchers said they were unable to conclude if any dietary factors might be protective because there simply weren't enough studies to draw any conclusions.
For now, both experts said maintaining a healthy weight can help prevent some cancers.
"Because we also have evidence linking obesity to other cancers and other chronic diseases, maintenance of healthy weight through a healthy diet and regular exercise is a safe bet to live a healthy life," Bandera said.
Explore further: Increasing height and body mass index are risk factors for ovarian cancer
Learn more about ovarian cancer from the American Cancer Society.