Women who are overweight for more than ten years have a higher risk of cancer, a leading scientist warns.
The chance of getting potentially deadly forms of the disease also increases as a person’s weight goes up, data revealed.
On average, every ten years of being fat upped the odds of cancer by 7 per cent.
But for women who were severely obese, the risk of breast cancer rose by 8 per cent every decade – and womb cancer by 37 per cent.
Excess weight is thought to feed at least ten types of cancer, including breast, womb, bowel, pancreatic and kidney.
Despite advances in medicine, the disease claims more than 160,000 lives a year in the UK, where 60 per cent of English women are overweight or obese.
Melina Arnold, of the International Agency for Cancer Research in Lyon, France, said it is important to make people aware of the obesity link, especially as once weight is put on it is hard to lose.
World Health Organisation researcher Dr Arnold, who worked with US colleagues, analysed data on almost 75,000 post-menopausal American women whose health was tracked for around 12 years.
They provided measurements from when they were 18, 35 and 50 years old. Some 40 per cent of the women had always been slim.
This left 60 per cent who had been overweight at some point – with almost half of these obese.
Some 6,300 of the women were diagnosed with cancer. And the longer they had been overweight, the higher their odds of the disease. The figures for endometrial cancer, which affects the lining of the womb, were particularly striking. The odds of the disease rose by 17 per cent, on average, for every decade a woman was overweight.
But for a severely obese woman, the risk increased by 37 per cent.
BMI is a measurement of weight related to height. Below 25 is healthy, between 25 and 29.9 overweight, and 30-plus obese.
A 5ft 3in woman who weighs 9 stone, has healthy BMI of 22.3. But at 11 stone, her BMI is 27.3 and she is overweight. If her weight creeps up to 12 and a half stone, her BMI goes into the obese range at 31. At 14 stone, she would have a BMI of 35 and classed as severely obese.
It is thought hormones released by fat in the body feed tumours.
The immune system may also release harmful chemicals and DNA may be damaged more, raising the odds of cancer.
Writing in the journal PLOS Medicine, Dr Arnold said it is important that women are aware of the link.
She said: ‘If we can prevent overweight and obesity from early on and promote maintaining a healthy weight, this would probably be a good strategy to reduce the prevalence of overweight and increase health.’
Fiona Osgun, of charity Cancer Research UK, said: ‘Obesity is the single biggest preventable cause of cancer after smoking, and is linked to ten different types.
‘This study only studied women but we know from other research that keeping a healthy weight can help reduce men’s risk of the disease too.’