Obesity Increases Cancer Risk, Analysis Of Hundreds Of Studies Shows

Following on from findings reported by the World Cancer Research fund last year, the study reveals that risk is increased not only in common cancers such as breast, bowel and kidney, but also in less common cancers such as blood cancers (myeloma and leukaemia) and melanoma (a form of skin cancer).

Dr Andrew Renehan and colleagues from the University of Manchester and Christie Hospital, did a meta-analysis (a combined analysis of  221 previous studies), looking at over 250,000 cases of cancer, to determine the risk of cancer associated with a 5kg/m² increase in body mass index (BMI).

The researchers found in men, a 5kg/m² increase in BMI raised the risk of oesophageal adenocarcinoma by 52%, thyroid cancer by 33%, and colon and kidney cancers each by 24%.

In women, a BMI increase of 5kg/m² increased the risk of endometrial (59%), gallbladder (59%), oesophageal adenocarcinoma (51%) and kidney (34%) cancers.

They also noted weaker, but significant, positive associations between increased BMI and rectal cancer and malignant melanoma in men; postmenopausal breast, pancreatic, thyroid, and colon cancers in women; and leukaemia, multiple myeloma, and non-Hodgkin's lymphoma in both sexes. They found associations were stronger in men than in women for colon cancer - 24% in men compared with 9% in women.

The study looked at cancer data from all over the world, and while the results for North America, Europe, Australia and the Asia-Pacific region were broadly similar, there was a stronger link between increased BMI and both premenopausal and post menopausal breast cancers in Asia-Pacific populations.

The senior author on the study, Dr Andrew Renehan, said: "This was a hugely comprehensive piece of research looking at 221 different studies in 20 types of cancer. For some cancer types, associations differ between sexes and populations of different ethnic origins and this should inform the exploration of biological mechanisms that link obesity with cancer."

He added: "Over the past five years, there was been increasing proof that obesity is linked with cancer risk, but despite this, we do not know whether weight reduction in people protects them against cancer. The findings of this study are important to address these issues and explore ways to prevent cancers in the future."

In an accompanying comment, Dr Susanna Larsson and Dr Alicja Wolk, Division of Nutritional Epidemiology, National Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden, say: "The number of deaths per year attributable to obesity is about 30000 in the UK and ten times that in the USA, where obesity has been estimated to have overtaken smoking in 2005 as the main preventable cause of illness and premature death."

They conclude: "Efforts will be needed to increase education on diet and physical activity, train health professionals, restrict advertisements of high-calorie and low-nutrient foods, limit access to unhealthy foods in schools and workplaces, levy taxes on sugary drinks and other foods high in calories, fat, or sugar, lower the prices of health foods, and promote physical activity in schools and workplaces. National cancer plans should include all these factors to reduce obesity, and thus decrease cancer incidence and increase survival."