'Strong evidence' of link between obesity and some major cancers, new study finds

A new study concludes there is "strong evidence" to support the association between obesity and 11 types of cancer, mostly of the digestive organs and hormone-related malignancies.

A team of international researchers looked at the data from 204 meta-analyses, which each combine the evidence from several individual studies. Using a new statistical technique called an "umbrella review", they were able to assess which cancers had the strongest associations with obesity.

The 11 cancers are:

• Oesophageal adenocarcinoma
• Multiple myeloma
• Cancer of the gastric cardia
• Colon cancer (in men)
• Rectal cancer (in men)
• Cancer of the biliary tract system
• Pancreatic cancer
• Postmenopausal breast cancer (where no hormone replacement therapy was used)
• Endometrial cancer (in premenopausal women)
• Ovary cancer
• Kidney cancer

The researchers found there to be "substantial uncertainty" regarding the associations between obesity and another 25 types of cancer. They acknowledged that there could be a valid association with those cancers too, but further study is required.

"Obesity is strongly related with a significant number of cancers, and there is no doubt this is the case," said the study's first author, Maria Kyrgiou, of Imperial College London.

"The main message is we have the evidence. We have to realize the moment an obese patient walks into our clinic, this is a patient who's at high risk," she said. It's hoped that doctors will be able to target personalized cancer prevention strategies to those individuals.

A public health issue

As rates of obesity rise in Canada and around the world, the latest research adds increased urgency to tackling the disease, which has also been associated with hypertension, diabetes, and osteoarthritis.

Statistics Canada reports that about 20 per cent of adults in Canada are obese. And worldwide, obesity has more than doubled since 1980, according to the WHO.

Kyrgiou said that makes reducing obesity a "phenomenal public health issue," on par with the efforts to decrease smoking that were undertaken in the past.

Preventing and treating obesity isn't easy

Dr. Arya Sharma, a professor of medicine and chair in obesity at the University of Alberta, said the latest research highlights the need for improved prevention and treatment of obesity.

"I think it's a reminder for all of us that we should be taking obesity far more seriously," he said.

Sharma noted the few available treatments for obesity are limited to bariatric surgery or a small number of drugs, which often aren't covered by benefit plans. He also noted that prevention often focuses on diet and exercise, when the causes of obesity can be more complex.

This latest research looked at observational studies, so it doesn't provide insight into how obesity might actually cause cancer.

But as researchers seek to answer that question, Kyrgiou said those cancers found to be strongly associated with obesity will provide a good place to start.