Obesity is strongly linked with developing and dying from several types of cancer including malignancies of the breast, ovary, kidney, pancreas, colon, rectum and bone marrow, a research review confirms.

Even though excess weight is thought to influence the odds of developing and dying from a wide variety of tumours, the study found “strong evidence” supporting this connection for just 11 cancers.

“Other associations could also be genuine, but there is still substantial uncertainty about them,” lead study author Maria Kyrgiou of Imperial College London said by e-mail.

Kyrgiou and colleagues analysed results from 204 previously published studies exploring the connection between obesity, weight gain, waist circumference and 36 different cancers.

They looked in particular for evidence that the previous results might have exaggerated the link between obesity and cancer or found a connection that wasn’t statistically significant.

They found the strongest links were between obesity and malignancies of the digestive organs and for hormone-related tumours in women, according to the report online in the British Medical Journal (BMJ).

They also found that increases in body mass index (BMI) were tied to a higher risk of developing cancers in the oesophagus, bone marrow, biliary tract system (liver, gall bladder and bile duct), pancreas and kidney. Upticks in BMI were also linked to greater odds of colon and rectal cancers in men as well as endometrial malignancies in younger women.

Researchers also found evidence of an association with other cancers but said existing studies did not provide a strong enough link.

The increased risk of cancer for every five-unit gain in BMI ranged from nine per cent for rectal cancer among men to 56 per cent for tumours in the biliary tract. For women, weight gain and waist-to-hip circumference ratio were also associated with an increased risk of certain cancers.

After menopause, women’s risk of breast cancer increased by 11 per cent for every five kilos of weight gained during adulthood. This was in women who didn’t use hormone replacement therapy, a treatment that is independently linked to an increased risk of breast cancer.

In addition, every 0.1 unit increase in waist-to-hip ratio was associated with a 21 per cent jump in the odds of endometrial cancer.

Researchers found strong evidence linking weight gain to colorectal cancer. They also found a strong connection between BMI increases and cancers of the gallbladder, stomach and ovaries, as well as death from bone marrow tumours.

More research is needed that assesses changes in body fat over time to better understand how obesity directly influences the risk of getting cancer or dying from the disease, the authors conclude.

The way obesity impacts the risk of cancer also varies in different parts of the body, Graham Colditz, a researcher at Washington University School of Medicine in St Louis, said by e-mail.

But the take-home message is the same for every patient, added Colditz, author of an editorial accompanying the study.

“Avoiding weight gain through adult years is important,” Colditz said. “Even if you are overweight, focus first on not gaining any more weight; for those who are overweight or obese taking off some kilos can lower cancer risk.”

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