"The burden of cancer due to being overweight or obese is more extensive than what has been assumed."
Being overweight can raise the likelihood of being diagnosed with cancers of the stomach and digestive tract, as well as certain brain and reproductive tumors, international researchers said Wednesday.
A report in the New England Journal of Medicine adds eight more kinds of cancer to the list of those already known to be more likely among overweight people.
In 2002, the World Health Organization's International Agency for Cancer on Research (IARC), based in France, said excess pounds could raise the risk of colon, esophagus, kidney, breast and uterine cancer.
Now, it has added stomach, liver, gall bladder, pancreas, ovary and thyroid cancers, as well as a type of brain tumor known as meningioma and the blood cancer multiple myeloma, the report said.
Researchers reviewed more than 1,000 studies of excess weight and cancer risks, saying that limiting weight gain over decades can help to reduce the risk of those cancers.
"The burden of cancer due to being overweight or obese is more extensive than what has been assumed," said IARC Working Group chair Graham Colditz of the Washington University School of Medicine in St. Louis.
"Many of the newly identified cancers linked to excess weight haven't been on people's radar screens as having a weight component."
Some 640 million adults and 110 million children around the world are obese
Cancer often arises with no explanation. Its causes can include viruses, pollutants, genetic factors and radiation.
Certain lifestyle factors such as smoking and being overweight can also make a person more likely to get cancer.
Around nine percent of cancers among women in North America, Europe and the Middle East are believed to be linked to obesity, the report said.
Extra fat can promote inflammation and lead to an overproduction of estrogen, testosterone and insulin -- all of which can drive cancer growth, the study added.
Some 640 million adults and 110 million children around the world are obese.
"Lifestyle factors such as eating a healthy diet, maintaining a healthy weight and exercising, in addition to not smoking, can have a significant impact on reducing cancer risk," Colditz said.
"This is another wake-up call. It's time to take our health and our diets seriously."