Researchers have linked obesity to eight more cancer types, bringing the number of cancers associated with excess weight to 13.

For a study published in The New England Journal of Medicine, researchers from the World Health Organization's International Agency for Cancer on Research (IARC) analyzed over 1,000 studies on cancer risk and excess weight. They found that excess weight or obesity is linked to eight more cancer types: stomach, gall bladder, liver, pancreas, meningioma (a brain tumor), ovary, multiple myeloma (a blood cancer) and thyroid.

And the higher the body-mass index of an individual, the higher their risks are for the newly linked cancer types.

The same researchers identified in 2002 that excess weight is linked to higher risks for uterus, breast, kidney, esophagus and colon cancers.

"The burden of cancer due to being overweight or obese is more extensive than what has been assumed," said Graham Colditz, M.D., Dr. P.H., IARC Working Group chair, adding that a lot of the cancers newly linked to obesity had not been commonly thought of as having a weight component.

Around the world, about 110 million children and 640 million adults are obese, including a third of children and adults in the United States. The results of the study can have a significant impact on the global population as the findings were consistent across geographic regions and genders.

According to Colditz, lifestyle factors have a big role in reducing cancer risk. He said that public health efforts geared toward fighting the disease should focus on things like promoting eating healthily, achieving a healthy weight, engaging in regular exercise and smoking cessation as these are factors that people can actually control.

However, the researchers acknowledge that losing weight is not an easy task. In fact, even those putting in a lot of effort into dropping those extra pounds have a hard time meeting their goals. Since losing weight may be too big of a task for some, the researchers suggest instead that they shift their focus to gaining less weight as this may be more manageable.

There are several reasons why obesity or excess weight has been linked to increased cancer risks. For starters, excess fat promotes an overabundance of insulin, testosterone and estrogen, and causes inflammation, which have been shown to support cancer growth.

To help combat obesity in children, the American Heart Association recently issued a recommendation limiting added sugars for children aged between 2 and 18 to less than 25 grams (0.88 ounce) or six teaspoons a day. Children younger than 2 years old are advised not to have added sugars at all in their diets because they have lower caloric needs.

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