12 September 2010 Last updated at 23:08 GMT
Colon cancer cases 'may rise 50%'
Exercise class Excess fat around the middle is a risk factor
The UK is heading for a 50% increase in the number of new colon cancer cases over the next 30 years, says an international team of scientists.
The forecast, in the European Journal of Cancer, is for 35,000 new cases a year by 2040, compared with 23,000 now.
Rising obesity is one reason - and if the UK reached US levels that could add another 2,000 to the total, they say.
The study used cancer data from seven countries to predict how cancer rates might change with an ageing population.
Each year there are 38,000 cases of bowel cancer, which can split into those in the colon and those lower down in the rectum. This latest study looked just at those in the colon itself.
Two of the biggest risk factors for colon cancer are physical inactivity and being overweight or obese.
Dr Andrew Renehan, from the University of Manchester, and one of the authors of the research, said that the computer models allowed researchers to predict what would happen to cancer rates in a variety of scenarios.
If UK trends in obesity and activity stayed as they are now, the predicted figure of approximately 35,000 cases a year is reached by 2040.
If obesity gets worse, following trends set in the US, where the problem has spiralled in recent years, then the annual figure is close to 37,000.
But if that does not happen, and there is a modest increase in activity, then that rise turns into a similar-sized fall.
And if the UK managed to match levels of physical exercise in The Netherlands - the best among the countries studied, that would prevent approximately 2,000 cases.
Dr Renehan said: "The predictive modelling is beginning to tease out the independent relevance of each of these factors in the prevention of colon cancer.
"We know that large numbers of colon cancer cases could be avoided by reducing exposure to risk factors."
Another researcher, Professor Jan-Willem Coebergh, from Erasmus University in The Netherlands, said: "We can safely say increasingly physical activity across Europe to the level already achieved in The Netherlands, where everybody cycles, would be of substantial benefit."
And a second study published at the same time appeared to show a small additional risk not just for obese people, but anyone carrying excess fat around their middle - even if their overall weight appears near-normal.
In the group studied, every additional inch of waistline from the slimmest to the biggest-waisted meant an extra 2% risk of bowel cancer, even when the BMI of the person was accounted for in the calculations.
The research, carried out by Imperial College London for the World Cancer Research Fund, combined the results of previous studies into the issue to produce more reliable evidence of the link.
Lifestyle changes and reduction of colon cancer incidence in Europe: A scenario study of physical activity promotion and weight reduction
* E. de Vries * , I. Soerjomataram * , V.E.P.P. Lemmens * , J.W.W. Coebergh * , J.J. Barendregt * , A. Oenema * , H. M?ller * , H. Brenner * , Andrew G. Renehan
Received 21 May 2010; received in revised form 15 July 2010; accepted 22 July 2010.
Across Europe, there are over 300,000 new cases of colorectal cancer annually. Major risk factors include excess body weight (usually expressed by a high body mass index, BMI) and physical inactivity (PA). In this study we modelled the potential long-term effects on colon cancer incidence of changes in prevalence of excess body weight and physical inactivity in seven European countries across Europe with adequate data.
We addressed the impact of interventions aimed at preventing weight gain and increasing physical activity on colon cancer incidence using the Prevent model as refined in the FP-6 Eurocadet project. Relative risk (RR) estimates were derived from meta-analyses; sex- and country-specific prevalences of BMI and PA were determined from survey data. Models were made for Czech Republic, Denmark, France, Latvia, the Netherlands, Spain and the United Kingdom.
In a hypothetical scenario in which a whole population had obtained an ideal weight distribution in the year 2009, up to 11 new cases per 100,000 person-years would be avoided by 2040. The population attributable fractions (PAF) for excess weight were much higher for males (between 13.5% and 18.2%) than for females (2.3--4.6%). In contrast, using the optimum scenario where everybody in Europe would adhere to the recommended guideline of at least 30min of moderate PA 5d per week, the PAFs for PA in various countries were substantially greater in women (4.4--21.2%) than in men (3.2--11.6%).
Sensitivity analyses were performed assuming underreporting of BMI by using self-reports (difference of 5 and 0.8 percent-points in males and females, respectively), using different risk estimates (between 5.8 and 11.5 percent-points difference for BMI for men and women, respectively, and up to 11.6 percent-points difference for PA for women).
Changes in lifestyle can indeed result in large health benefits, including for colon cancer. Two interesting patterns emerged: for colon cancer, achieving optimum BMI levels in the population appears to offer the greatest health benefits in population attributable fractions in males, while increased physical activity might offer the greatest fraction of avoidable cancers in females. These observations suggest a sex-specific strategy to colon cancer prevention.
Keywords: Body mass index, Physical activity, Colon cancer, Modelling, Prediction
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