There’s ‘strong evidence’ obesity is tied to 11 types of cancer, study warns

Obesity linked to 11 different cancers: study
WATCH: British researchers suggest there's "strong evidence" tying obesity to 11 different cancers.

If you’ve been trying to lose weight, British scientists are giving you an important incentive: new research is warning that there is “strong evidence” that obesity is linked to 11 different cancers.

The association between excess body weight and the disease is “significant,” scientists out of Imperial College London say. They studied 36 cancers and warned that the link to other cancers may exist but, for now, they’re shrouded in “substantial uncertainty.”

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“It is now clear that preventing excess weight may reduce the risk of developing certain forms of cancer. With this information, it is crucial that the health-care system intensifies efforts to reduce cancer associated with obesity,” Dr. Kostas Tsilidis, one of the study’s lead authors, said in a university statement.

Tsilidis’ team hopes their findings will help identify patients grappling with obesity or being overweight and screen them in case they’re at high risk for cancer.

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Tsilidis’ study is a review, combing over 204 studies from 49 publications that looked at obesity measurements, from body mass index to waist circumference, and 36 different types of cancer.

By scouring through the data, the researchers uncovered which cancers were most strongly linked to obesity.

The 11 cancers tied to obesity are:

  • Colon (in men)
  • Rectal (in men)
  • Pancreatic
  • Ovary
  • Kidney
  • Endometrium
  • Postmenopausal breast cancer (when HRT – or hormone replacement therapy wasn’t used)
  • Biliary tract
  • Multiple myeloma
  • Esophageal
  • Bone marrow

In 95 of the studies, 13 per cent of associations were supported by “strong evidence.” That means the results were strong and there was no suggestion of bias.

(The researchers note that past studies and reviews suggested links between obesity and some cancers, but that the work may be flawed or biased because of study design.)

READ MORE: Trying to lose weight? Study links excess weight, obesity to at least 8 cancers

The other papers in the umbrella review came up with highly suggestive (18 per cent), suggestive (25 per cent) ties between weight and cancer risk.

For 25 types of cancer, the evidence wasn’t strong enough.

Across the board, the risk of developing cancer for every five-point jump in BMI ranged from nine per cent for colorectal cancer among men to 56 per cent for biliary tract system cancer.

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In women, postmenopausal breast cancer risk increased by 11 per cent for every five kilograms of weight they put on.

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This isn’t the first time scientists pointed to obesity as a risk factor for cancer.

Last August, the World Health Organization’s International Agency for Research on Cancer (IARC) warned that excess weight is tied to at least eight types of cancer:

  • Stomach
  • Liver
  • Gall bladder
  • Pancreas
  • Ovary
  • Thyroid
  • Blood (multiple myeloma)
  • Meningioma (a type of brain tumour)

“The burden of cancer due to being overweight or obese is more extensive than what has been assumed. Many of the newly identified cancers linked to excess weight haven’t been on people’s radar,” Dr. Graham Colditz, a Washington University School of Medicine professor and chair of the IARC’s working group, said.

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“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 … 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,” he suggested in a statement.

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The latest findings have global reach: an estimated 640 million adults and 110 million children are categorized as obese. In Canada, one in four Canadian adults is clinically obese, according to the Canadian Obesity Network.

There are about 14 million obese or overweight adults in the country, along with another 500,000 kids grappling with weight gain, according to Statistics Canada.

The medical community has already established excess weight as a risk factor for heart disease, diabetes, and cancer among other conditions.

Over the past few decades, the IARC has studied more than 1,000 things — including chemicals, food and radiation — to see if they could be tied to cancer risk.

READ MORE: Alcohol doesn’t cause cancer, but these things might, according to the WHO

In 2002, for example, it found “sufficient evidence” linking excess weight to higher risks of cancers in the colon, esophagus, kidney, breast and uterus.

Read the Imperial College London research published in the BMJ.