Being overweight significantly increases the risk for cancer, according to a new report that found excess body weight responsible for 481,000 new cancers, or 3.6 percent of the cases worldwide, in 2012.
The study by the International Agency for Research on Cancer in Lyon, France, said the prevalence of obesity in adults had doubled since 1980, accounting for a significant share of cancers.
The study by IARC, a research arm of the World Health Organization, found cancer poses a greater health problem for obese women, who developed 2-1/2 times more cases of cancer than overweight men did in 2012.
Most of the 345,000 new cancers in women involved reproductive organs, including the uterus and womb, or breast cancer in post-menopausal women.
Lead researcher Melina Arnold said there are different mechanisms by which excess weight causes cancer.
“For example, for breast cancer, we know that one of the pathways is related to hormones that are produced by fat tissue, and that can lead to cancer development," she said.
Cancers of the colon and kidney accounted for nearly 90,000 cases of the disease among men, according to Arnold’s report.
Esophageal cancer, or cancer of the gullet, is another common cancer worldwide, particularly among overweight men.
“One of the main risk factors is reflux of gastric acid," Arnold said. "And we know this reflux is more common in obese people.”
The IARC study is the first to link excess weight to a specific number of cancer cases. Researchers looked at data from the GLOBOCAN cancer database for 184 countries.
Most of the new cancer cases were found in the developed world. Twenty-three percent of the obesity-related cancers occurred in North America, while sub-Saharan Africa only contributed 7,300 cancers, or 1.5 percent of the cases.
But obesity is a growing health problem worldwide, and researchers expect that trend to be reflected in an increasing number of cancers in the next 10 to 20 years.
For example, Arnold said, North Africa has seen the largest increase in obesity during the past three decades and could also experience a sharp increase in cancer cases.
“We need to raise awareness in the population that obesity can cause cancer," she said.
The study on the global burden of cancer caused by overweight and obesity is published in the journal The Lancet Oncology.