Half of all cases of womb cancer and a type of oesophageal cancer in women are as a result of being overweight or obese, according to a new report published online in the British Medical Journal.

This study provides the first reliable evidence on the relevance of being overweight or obese for a wide range of cancers in women in the UK today.

Its findings suggest that among middle aged and older women in the UK, around five percent of all cancers, that is 6000 cancers each year, are as a result of by being overweight or obese.

As well as pinpointing womb cancer and one type of oesophageal cancer as examples where being overweight or obese is a major risk factor, the study also finds that excess weight increases the risk of kidney cancer, leukaemia, multiple myeloma, pancreatic cancer, non-Hodgkin’s lymphoma, ovarian cancer and, in some age-groups, breast and bowel cancer.

The Million Women Study, funded by Cancer Research UK, is the biggest study ever undertaken to look at women and cancer risk. Over one million UK women were studied during seven years. More than 45,000 cases of cancer and 17,000 cancer deaths occurred during that time.

Lead researcher Dr Gillian Reeves, Cancer Research UK epidemiologist based at Oxford University, said: “Based on our findings, we estimate that being overweight or obese accounts for around 6,000 out of a total 120,000 new cases of cancer each year among middle-aged and older women in the UK.

“Our research also shows that being overweight has a much bigger impact on the risk of some cancers than others. Two thirds of the additional 6000 cancers each year due to overweight or obesity would be cancers of the womb or breast.”

But the research found that the relationship between body mass index (BMI)* and cancer also depended on a woman’s stage of life. For example, being overweight increases the risk of breast cancer only after the menopause and the risk of bowel cancer only before the menopause.

Sara Hiom, director of Cancer Research UK’s health information, said: “This research adds to the evidence regarding the impact of being overweight or obese on developing cancer and dying from the disease.

“While most people readily associate carrying extra weight with being a general health risk, many do not make a specific link with cancer. These findings need to be taken into consideration alongside the established strong relationships between body fatness and other common illnesses such as diabetes and heart attacks.”

*BMI= Weight divided by Height Squared