A major study has revealed obesity strongly increases the risk of developing 11 types of cancer. Being overweight is probably linked to many other forms of the illness but so far there is not enough evidence, researchers say.

Types linked to obesity include breast, oesophagus, stomach, bowel, rectum, biliary tract system, pancreas, womb, ovary, kidney and the blood cancer myeloma.

Researchers from Imperial College London, United Kingdom (U.K.), calculated that men’s risk of developing biliary tract cancer increases by up to 56 per cent for every 11lb gained in weight.

For women, the risk of womb cancer rises by 21 per cent for every 0.1 point increase in hip to waist ratio. The findings are particularly concerning as a quarter of adults and a fifth of 11-year-olds are classed as obese.

The research, published in the British Medical Journal, highlighted previous figures showing that up to 25,000 cancer cases in the UK could be prevented each year if everyone was a healthy weight.

It looked at 204 existing studies which examined the link between obesity and cancer. The international team of researchers, led by Maria Kyrgiou and Kostas Tsilidis from Imperial College London said there could be associations between obesity and other cancers, but substantial uncertainty remains because the quality of evidence is not strong, say

They call for more research because “evidence of the strength of the associations between obesity and cancer may allow finer selection of people at high risk, who could be selected for personalised primary and secondary prevention strategies.”

Cancer is a leading cause of death worldwide, and the prevalence of obesity has more than doubled over the past 40 years. Previously published evidence supports the association between obesity and some cancers, but some may be flawed or biased due to weak study design and conduct.

Therefore, in a bid to determine the quality of evidence and the strength of these associations, the researchers conducted a comprehensive review of studies on obesity and risk of developing cancer.

After a literature search, they identified 204 studies from 49 publications that analysed the obesity measurements, such as body mass index (BMI), weight gain, and waist circumference, and 36 cancers and their subtypes.

Of the 95 studies that included continuous obesity measures, only 13% of associations were supported by strong evidence, meaning the studies had statistically significant results and no suggestion of bias.

Strong associations were found in studies that examined BMI with risk of oesophageal, bone marrow, and colon (in men), rectal (in men), biliary tract system, pancreatic, endometrial (in premenopausal women), and kidney cancers.

Risk of developing cancer for every 5 kg increase in BMI ranged from nine per cent for colorectal cancer among men, to 56 per cent for biliary tract system cancer.