Wednesday September 15 2010
Losing weight is one measure estimated to cut cancer risk
“Colon cancer cases may rise 50%,” BBC News reported. The website said factors such as increasing levels of obesity and inactivity could drive cases up from 23,000 a year to 35,000 annual cases by the year 2040.
This report was based on a study that made projections of future levels of colorectal cancer if obesity and physical activity remain at their current levels. It compared these projections to hypothetical situations where everyone had optimum weight and exercise levels. An optimum body mass index (BMI) was predicted to reduce cases of colorectal cancer by up to 18.2% in men and 4.6% in women. Optimum physical activity levels could reduce the risk by 11.6% in men and 21.2% in women.
This was a hypothetical model and these figures are only estimates that need further confirmation. However, in general, it is well established that maintaining a healthy weight, eating a balanced diet, getting enough exercise and avoiding smoking and excess alcohol are the best ways to remain healthy.
Where did the story come from?
The study was carried out by researchers from University Medical Center, Rotterdam, and other institutions in the Netherlands, UK and Australia. It was funded by EUROCADET research group. The study was published in the peer-reviewed European Journal of Cancer.
BBC News accurately reflected the issues raised by this journal article.
What kind of research was this?
The researchers reported that 300,000 new cases of colorectal cancer are diagnosed every year in Europe. High BMI and low levels of physical activity are considered to be important risk factors. This study aimed to construct a hypothetical model to see how changes in levels of obesity and low physical activity seen across Europe could influence the incidence of colorectal cancer.
What did the research involve?
This model intended to show how reducing obesity and increasing activity might affect the number of cases of colorectal cancer in the future, and compared these estimates to the current situation of rising obesity.
To do this, the researchers used the Prevent computer programme, which calculates the change in future cancer incidence according to different scenarios of changes in risk factors. It also determines the size of a particular risk factor as a “population attributable fraction” (PAF). For example, the PAF for obesity would be the reduction in colorectal cancer that would be expected if everyone had an ideal BMI. For physical activity, the PAF was calculated according to everyone getting their recommended level of exercise (30 minutes of moderate exercise five times a week).
The model used gender-specific demographic data, data on the prevalence of risk factors and cancer incidence figures determined from survey data for the Czech Republic, Denmark, France, Latvia, the Netherlands, Spain and the UK. The model also relied on data from recent systematic reviews, which had calculated how much raised BMI and lower physical activity increased the risk of colorectal cancer.
What were the basic results?
The researchers calculated that if a whole population reached an ideal BMI in the year 2009, up to 11 new cases of colorectal cancer per 100,000 person-years would be avoided by 2040. Person-years take into account the number of years of follow-up and the number of people in a study. For example, two person-years could be one person followed for two years or two people for one year. The prevention of 11 cases over 100,000 person-years of follow-up is a relatively small number.
The population attributable fractions for being overweight and obese were found to be much higher for men (between 13.5% and 18.2%) than for women (between 2.3% and 4.6%). This means that if all men had an ideal BMI, the number of male cases of colorectal cancer would reduce by up to 18.2%, but only by up to 4.6% in women. This suggests that obesity has less influence on colorectal cancer risk in women.
By contrast, if everyone managed to do the recommended minimum of 30 minutes of moderate-intensity physical activity on five days a week, cases of colorectal cancer would reduce by 3.2% to 11.6% in men and by 4.4% to 21.2% in women. This suggests that physical activity has a greater influence on colorectal cancer risk in women.
How did the researchers interpret the results?
The researchers concluded that changes in BMI and physical activity can influence the incidence of colorectal cancer. Two main patterns emerged: achieving an optimum BMI in the population appeared to give the greatest benefits for men, while increased physical activity might offer women the greatest protection against cancer.
This modelling study has made projections on how the future incidence of colorectal cancer could be affected by modifying obesity and physical activity levels in the population. It compared these optimum situations with current trends of obesity and inactivity and found that if everyone in the population had an optimum BMI, it would reduce incidence of colorectal cancer by up to 18.2% in men and 4.6% in women. If everyone did the recommended amount of physical activity, it could reduce colorectal cancer by up to 11.6% in men and 21.2% in women.
This is only a hypothetical model and these figures are estimates. Also, several assumptions needed to be made in this model. The BMI and physical activity levels obtained for each country were self-reported by the public, which may introduce some inaccuracy. However, the researchers took this into account in their calculations. The model also incorporated risk figures taken from previous systematic reviews to tell them how much obesity and inactivity would increase the risk of colorectal cancer. The accuracy of these risk figures therefore depends on the reliability of the systematic review, and the methods and quality of the trials that the review itself included.
In general, it is well established that the best ways to stay in good health are to maintain a healthy weight, eat a balanced diet, take regular exercise and avoid smoking and excess alcohol. While not all disease risk factors can be eliminated as medical and hereditary factors frequently play a role in disease risk, this study supports the benefits of a healthy lifestyle, which may reduce the risk of several diseases, including some cancers.