Washington, Aug 25 (PTI): Being obese or overweight may lead to eight more types of cancer than previously thought, new research has warned.

Researchers have identified eight additional types of cancer linked to excess weight and obesity: stomach, liver, gall bladder, pancreas, ovary, meningioma (a type of brain tumour), thyroid cancer and the blood cancer multiple myeloma.

Limiting weight gain over the decades could help to reduce the risk of these cancers, researchers said.

The findings are based on a review of more than 1,000 studies of excess weight and cancer risk analysed by the World Health Organisation's International Agency for Cancer on Research (IARC), based in France.

"The burden of cancer due to being overweight or obese is more extensive than what has been assumed," said cancer prevention expert Graham Colditz, at Washington University School of Medicine in the US.

"Many of the newly identified cancers linked to excess weight have not been on people's radar screens as having a weight component," said Colditz, who chaired the IARC Working Group.

The findings could have a significant bearing on the global population. Worldwide, an estimated 640 million adults and 110 million children are obese, researchers said.

In 2002, the same group of cancer researchers found sufficient evidence linking excess weight to higher risks of cancers of the colon, esophagus, kidney, breast and uterus.

"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.

"Public health efforts to combat cancer should focus on these things that people have some control over.

"But losing weight is hard for many people. Rather than getting discouraged and giving up, those struggling to take off weight could instead focus on avoiding more weight gain," said Colditz.

For most of the cancers on the newly expanded list, the researchers noted a positive dose-response relationship: the higher the body-mass index, or BMI, the greater the cancer risk.

The cancer risks associated with excess weight were similar for men and women and, when data were available, were consistent across geographic regions - North America, Europe, Asia and the Middle East, researchers said.

There are many reasons why being overweight or obese can increase cancer risk, they noted.

Excess fat leads to an overproduction of oestrogen, testosterone and insulin, and promotes inflammation, all of which can drive cancer growth.

The finding was published in The New England Journal of Medicine.