According to the International Obesity Task Force, an estimated 300m adults worldwide are obese (body mass index over 30). "Conservative estimates suggest that obesity levels will continue to rise in the early 21st century - with severe health consequences - unless urgent action is taken now," says the organisation. But the authors of the new study, published ahead of print in the journal Gut, note that rates of oesophageal cancer have also been rising fast - in some countries faster than other forms of cancer. Epidemiological studies have already implicated a connection between gastro-oesophageal reflux and oesophageal adenocarcinoma; and obesity and overweight are associated with increased prevalence of gastro-oesophageal reflux symptoms. People who suffer from acid reflux are already advised to abstain from certain foods and drinks, such as citrus fruits, tea and coffee, raw onion, alcohol, ice cream and chocolate. But the researchers from Queensland Institute of Medical Research, Australia, who worked in collaboration with the Australian Cancer Society, think that overall obesity (which may be a result of eating habits, lifestyle, genetic makeup, or a combination of factors) could also be a cause. "Obesity has been linked with markedly increased risks of other cancers, and thus there are plausible grounds for speculating that high levels of body fat may promote carcinogenesis though other pathways," they said. "These alternative causal hypotheses remain largely untested for oesophageal cancers." The researchers, led by David Whiteman, conducted a population-based case control study involving 1181 patients ages between 18 and 79 years with oesophageal cancer. Almost 1600 controls were randomly selected from the electoral register. Data were collected using self-completed mailed questionnaires, which included information on body mass index, cigarette-smoking, alcohol consumption, and frequency of symptoms of gastro-oesophageal reflux in the ten years prior to diagnosis. Whiteman and his team found that people who were clinically obese - that is, with a BMI over 30 - had a much higher risk of developing the disease than those in the healthy weight bracket, regardless of whether they suffered from reflux or not. Those with a BMI over 40 were as much as six times more likely to develop oesophageal cancer as those with a BMI between 18.5 and 25. These findings held true even when smoking and alcohol consumption were taken into consideration. While observing that obesity seems to be an independent risk factor for the disease, the researchers sought to offer some explanation. They noted that higher levels of fat and tissue in the body boost insulin production, which in turn increases the amount of circulating insulin-like growth factor. These hormones stimulate cell growth and curb cell death, conditions which also favour cancer development. Moreover, fat cells also produce other hormones known as adipocytokines, which speed up cell growth and are involved in inflammatory processes. Journal: Gut (published online ahead of print) DOI: 10.1136/gut.2007.131375 Title: "Combined effects of obesity, acid reflux, and smoking on the risk of adenocarcinomas of the oesophagus" Authors: David Whiteman, Shahram Sadeghi, Nirmala Pandeya, Mark Smithers, Dabid Gotley, Christopher Bain, Penelope Webb, Adele Green.