Wednesday October 27 2010
People with healthy lifestyles had a lower risk of bowel cancer
Researchers have identified five lifestyle changes that could cut the risk of bowel cancer by 23%, the Daily Mail reported. It said that one in four cases of bowel cancer could be prevented if people drank less alcohol, cut down on red meat, took more exercise, watched their waist size and stopped smoking.
This Danish study enrolled 57,053 adults aged 50 to 64 without cancer. Measurements of lifestyle risk factors for colorectal cancer were taken at the beginning of the study. Their cancer incidence was then tracked over the next 10 years. People who followed public health recommendations (not smoking, a healthier diet, etc.) for each of these areas had a lower risk of developing colorectal cancer during this time.
The newspaper report is well balanced. This was a large, well-conducted study, and the findings are further evidence that changeable lifestyle factors affect the risk of cancer, including colorectal cancer. The research has some limitations, such as its inability to show the exact contribution of each lifestyle factor, and how following the recommendations at different stages of life affects cancer risk.
Where did the story come from?
The study was carried out by researchers from the Institute of Cancer Epidemiology and Aarhus University, both in Denmark, and was funded by the Danish Cancer Society. It was published in the peer-reviewed British Medical Journal.
The study was generally well reported in a number of newspapers. Most of them reported both the overall reduction of risk and the fact that following the recommendations in just one area can make a great difference to risk.
What kind of research was this?
This study investigated how a number of lifestyle risk factors affect the likelihood of developing colorectal cancer. It used a cohort study design and, for a number of years, followed a large number of people who did not have cancer to see who developed the disease.
Colorectal cancer is one of the most common cancers in developed countries. More than 100 new cases are diagnosed in the UK each day. Several lifestyle factors can contribute to the risk of this cancer, including physical activity, smoking, alcohol intake, waist circumference and diet.
This study focused on whether following the public health advice for these factors affects the risk of developing the cancer, and whether there is a greater reduction in risk if more recommendations are followed. The study design is an appropriate choice for this type of research question, although it may be beneficial to follow the participants for longer, as colorectal cancer can take a long time to develop. It might also have been been useful to monitor whether people followed the recommendations over time, as this study only measured people’s adherence at the start of the study.
What did the research involve?
Between 1993 and 1997, 57,053 people aged between 50 and 64 were recruited to the Diet, Cancer and Health Cohort Study in Copenhagen. Participants were selected if they had no previous diagnosis of cancer according to the Danish Cancer Registry. Each participant was asked to fill in a questionnaire asking about their current smoking, alcohol consumption, physical activity (from work and exercise) and diet. The questionnaire also contained questions on a number of other lifestyle, health and social factors. Some body measurements, such as waist circumference, were also collected.
From the data collected at the start of the study, each participant was given a score on a lifestyle index scale, according to how many areas in which their lifestyle or measurements matched the recommendations from the World Health Organization, the World Cancer Research Fund and the Nordic Nutrition Recommendations. A score of zero indicated the least healthy lifestyle and a score of five indicated the healthiest. One point was allocated for each of the following:
- Not smoking.
- Being physically active for at least 30 minutes per day or having a job with light or heavy manual activity.
- Waist circumference of less than 88 cm for women and 102cm for men.
- Weekly alcohol consumption of fewer than seven alcoholic drinks for women and 14 for men.
- A ‘healthy diet’, defined as eating more than or equal to 600g of fruit and vegetables per day, less than or equal to 500g of red and processed meat per week, more than or equal to 3g of dietary fibre per megajoule (MJ) of dietary energy, and less than or equal to 30% of total dietary energy from fat.
Cases of colorectal cancer were detected in the follow-up period from the Danish Cancer Registry (median follow up time 9.9 years). Data was also collected from the Central Population Registry to monitor death from other causes, or emigration.
The researchers then calculated whether there was an association between a person’s score on the lifestyle index scale and whether they developed colorectal cancer in the follow-up period. The researchers adjusted their results for variables known or thought to be associated with colorectal cancer, such as family history, use of aspirin-like drugs and hormone replacement therapy.
What were the basic results?
Of the 57,053 people initially recruited, 55,487 were included in the analysis. Some were excluded if they were diagnosed with cancer shortly after the start of the study, or if information from the questionnaire was missing. Of the participants analysed, 8% scored zero or one on the lifestyle index scale, 26% scored two, 40% scored three, 25% scored four and 1% scored the maximum of five. There were 678 cases of colorectal cancer detected during the follow-up period.
People who had higher scores on the lifestyle index scale had lower incidence of colorectal cancer. After taking into account potential confounders, such as family history, an increase of one point on the lifestyle index scale gave an incidence rate ratio of 0.89 (95% Confidence interval [CI] 0.82 to 0.96).
When limiting the analysis to just men or women, this association was still significant for men (incidence rate ratio 0.85, 95% CI 0.76 to 0.94) but not for women. When separating the cancers into subtypes of cancer (colon or rectal), the association between healthy lifestyle and colon cancer remained (incidence rate ratio 0.88, 95% CI 0.80 to 0.98), but was not observed for rectal cancer.
How did the researchers interpret the results?
The researchers say that “following the public health recommendations on smoking, alcohol intake, physical activity, waist circumference, and diet was associated with a substantially lower risk of colorectal cancer”.
They estimated that if all the participants had followed the health recommendations for all five risk factors, 23% of colorectal cancer cases could have been avoided (95% CI 9% to 37%). If every person had followed one additional recommendation, the number of cases would have been reduced by 13% (95% CI 4% to 22%).
These findings are further evidence that lifestyle factors affect the risk of cancer, including colorectal cancer. Although the greatest reduction in risk is seen when people follow the recommendations in all areas, just sticking to the guidelines in one additional area reduces a person’s risk.
This was a large, well-conducted study. There are, however, some limitations:
- The lifestyle factors were measured on a single occasion at the start of the study. It is possible, and even probable, that people change their behaviour over time, and this might affect their overall risk.
- Colorectal cancer takes a long time to develop. This study followed people for about 10 years, from the ages of 50 and 64. The results therefore may not reflect how following the recommendations throughout adulthood, or at a particular stage in life, affects cancer risk.
- Some of the lifestyle factors included in the study, such as diet and alcohol intake, can be difficult to measure, as people are prone to underestimating or overestimating their consumption of alcohol and some food types.
- It is possible that there are other factors, for example, lifestyle or socioeconomic factors, which may also contribute to cancer risk but were not measured or adjusted for in the analysis. The size of the effect may have been reduced had these been taken into account.
Further studies that follow people for longer and measure their adherence to health recommendations over a longer period may support the findings of this research. Few people were found to achieve all five areas of healthy living, and further research into how to change this may be beneficial.