Being fat could become the biggest cause of cancer in women, warn researchers Last updated at 8:36 PM on 24th September 2009 Danger: Being fat could become the leading cause of cancer in women in Western countries New predictions about the impact of obesity suggest it could soon overtake smoking as the key trigger for cancers such as those of the bowel, womb and breast. Almost one in ten new cases of the disease among women in Europe are currently attributed to being overweight or obese - almost three times more than men - according to data presented at a major conference in Berlin. At least 13,000 cases of cancer are blamed on obesity in Britain, out of almost 300,000 cases diagnosed each year. Cancer expert Dr Andrew Renehan, said: Obesity is catching up at a rate that makes it possible it could become the biggest attributable cause of cancer in women within the next decade.' His team designed a model to estimate the number of cancers caused by overweight, which a BMI (body mass index) of 25 or more - in 30 European countries. In 2002, they calculated that 70,000 cases of cancer out of about 2 million cancer cases were attributable to being overweight or obese in 30 European countries. By 2008, the number had jumped to at least 124,050 - approaching double. In men, 3.2 per cent of new cancers could be attributed to being overweight or obese and in women it was 8.6 per cent. Obesity related cancers in the UK were 4.8 per cent for women and 3.3 per cent for men. Cancer of the womb lining, post-menopausal breast cancer and bowel cancer accounted for the largest numbers of weight-related cancers. Scientists believe fat tissue affects cancer risk by increasing levels of hormones such as insulin and oestrogen. Smoking currently accounts for one in four cancer deaths in men and women - by far the biggest single cause of the disease. But as more people quit, experts predict this figure will drop and be overtaken by obesity as the leading cause of the disease. Dr Renehan said a fall in the number of women on Hormone Replacement Therapy following fears about breast cancer may have boosted the number of cancers attributed to obesity, HRT use may have masked and diluted the effect of being overweight on the incidence of the disease. He said: 'In women who used HRT it wasn't clear what proportions of breast cancers were caused by HRT or by obesity. In women who don't take HRT, the effect of obesity was much clearer. 'Now that far fewer women are using HRT, it is much easier to see the effect of obesity on the incidence of breast cancer, and also on endometrial cancer. Consequently, the proportions of these cancers attributable to obesity have increased.' Dr Renehan added: 'I must emphasise that we are trying not to be sensationalist about this. These are very conservative estimates, and it's quite likely that the numbers are, in fact, higher.' The number of cases of obesity-related oesophageal cancers was especially high in the UK, where there are around 2,000 cases a year. 'This country accounts for 54 per cent of new cases across all 30 countries' said Dr Renehan. 'This may be due to synergistic interactions between smoking, alcohol, excess body weight and acid reflux - and is currently an area where research is required.' Henry Scowcroft, Cancer Research UK's science information manager, said 'Although the numbers differ from other similar analyses, this is a good, strong study which confirms that obesity is an important avoidable cause of cancer. 'These results provide important and sobering projections for the present and future impact of obesity on European cancer rates.' Scientists aren't sure why being fat boosts your cancer risk, but suspect it is connected to hormones. As people become fatter, they produce more hormones like estrogen that help tumors grow. People with big bellies also have more acid in their stomachs, which can lead to stomach, intestinal or esophageal cancer. Still, not all experts said obesity would produce skyrocketing cancer rates in the near future. 'It is not likely (obesity) will have as severe an effect as smoking,' said Jan Coebergh, a professor of cancer surveillance at Erasmus University, who has done similar research. Coebergh expected it would take a few decades before rounder Europeans would see a parallel rise in cancer, since the disease often takes years to develop. Still, scientists called for more measures to fight obesity and the cancers it might cause. Renehan said new strategies were needed to help people stay slim. 'We need to find the biological mechanism to help people find other ways of tackling obesity,' he said. 'Just telling the population to lose weight obviously hasn't worked.'