Overweight and obesity have become major risk factors for cancer, causing almost half a million new cases of the disease worldwide every year, a new study has found.

According to the International Agency for Research on Cancer (IARC), cancer caused by excess weight is currently much more common in more developed countries - accounting for over 5% of all new cancer cases in these countries - compared to less developed countries, where just 1.5% of cases are due to overweight or obesity.

Furthermore, the proportion of cancers linked to obesity is higher in women than in men. In fact, women are ‘disproportionately affected by obesity-related cancers'.

"For example, for postmenopausal breast cancer, the most common cancer in women worldwide, the study suggests that 10% of these cancers could have been prevented by having a healthy body weight," noted one of the study's lead authors, Dr Melina Arnold, of the IARC.

Overall, cancers of the breast, endometrium and colon account for almost three in four cancers linked to excess weight in women. Colon and kidney cancers account for two in three of all weight-related cancers in men.

Meanwhile, the countries with the highest cancer burden attributable to excess weight in men are the Czech Republic (5.5% of that country's new cases of cancer), Jordan (4.5%) and the UK (4.4%). Among women, the highest weight-related cancer burden is found in Barbados (12.7%), the Czech Republic (12%) and Puerto Rico (11.6%).

Dr Kate Allen of the World Cancer Research Fund International, which funded the study, described the findings as ‘worrying'.

"These worrying results highlight that it's crucial to maintain a healthy weight to prevent so many common cancers. Cancer is an epidemic problem, and to tackle it we need to help people take measures to be a healthy weight," she said.

The study pointed out that if populations had maintained their average body mass index (BMI) of 30 years ago, one in four cases of cancer attributable to excess weight - around 118,000 cases - could have been prevented.

"The number of cancers linked to obesity and overweight is expected to rise globally along with economic development. This study stresses the importance of putting in place efficient weight control measures, to curb the high number of cancers associated with excess body weight and to avoid the problems faced by rich countries being repeated in those now undergoing rapid development," added IARC director, Dr Christopher Wild.

Details of these findings are published in the journal, The Lancet Oncology.

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