Being overweight doubles the risk of certain cancers in women, Britain's largest study of the link between weight and malignant disease has found. Increasing obesity in the UK and the Western world is fuelling the growth in cancer and urgent measures are needed to halt it, researchers say.

While the risks of carrying excess body fat for heart disease, stroke, diabetes and high blood pressure are well documented, less attention has been paid to the link with cancer. Out of 17 forms of the disease examined, an increase in body mass index (BMI) raised the risk of 10 of them but had no effect on the remainder. Overall, being overweight or obese accounts for one in 20 cancers – or 6,000 of the 120,000 cases diagnosed each year.

The findings support a study by the World Cancer Research Fund, which said the evidence of a link between obesity and cancer was stronger than ever. The new research, published in the online edition of the British Medical Journal, is based on data collected for the Million Women study, the largest examination of cancer risk in women. More than one million British women aged 50 to 64 were monitored for seven years, during which time 45,000 of them were diagnosed with cancer and 17,000 died from the disease.

Half of the 6,000 cases of endometrial cancer (cancer of the womb) diagnosed in Britain each year are caused by the patient being overweight or obese, the report says. Excess weight is also a major risk factor in one kind of oesophageal cancer (cancer of the gullet). It is also found to increase 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.

Cancer Research UK, which funded the study, said it provided the first reliable evidence on the relevance of being overweight or obese for a wide range of cancers in women. Gillian Reeves, an epidemiologist who led the research at Oxford University, said: "Based on our findings, we estimate that being overweight or obese accounts for around 6,000 out of a total of 120,000 new cases of cancer each year among middle-aged and older women in Britain. Being overweight has a much bigger impact on the risk of some cancers than others. Two-thirds of the additional 6,000 cancers each year due to being overweight or obese would be cancers of the womb or breast."

Ms Reeves added: "We don't want to give the impression that being overweight is in the same league as smoking, but it is a risk factor and people need to be aware of it."

Ms Reeves's team found that the relationship between body mass index (BMI) and cancer also depend on a woman's stage of life. For example, being fat only increases the risk of breast cancer after the menopause, and only makes bowel cancer more likely before the menopause.

The increased risk from obesity

Increased risk of cancer associated with an increase in body mass index from normal weight to obese (10 units) among post-menopausal women not taking HRT

* Womb 189 per cent

* Oesophagus 138 per cent

* Bowel (in pre-menopausal women) 61 per cent

* Kidney 53 per cent

* Leukaemia 50 per cent

* Breast 40 per cent

* Bone marrow (myeloma) 31 per cent

* Pancreas 24 per cent

* Non-Hodgkin's lymphoma 17 per cent

* Ovarian 14 per cent