Colorectal Cancer (Crc): Impact Of Dietary And Lifestyle Risk Factors

Colon rectal cancer (CRC) is the third most common non-skin cancer and the second leading cause of cancer-related mortality in men and women in the US and other developed countries. Approximately 1 million new cases of CRC are diagnosed every year, and more than half a million people die from this disease, equivalent to approximately 8% of all cancer-related deaths worldwide. Both men and women have similar incidence and mortality rates through age 50 - after 50 years, these rates are higher in men. There were close to 150,000 new cases of colon and rectal cancer in the US in 2010 with over 50,000 deaths overall, according to the National Cancer Institute.

Given the high incidence rates for CRC seen in certain areas and ethnic groups in the US, Canada, Japan and New Zealand, health experts believe that lifestyle risk factors including diet, physical activity, obesity and diabetes play a key role in the development of the disease. High consumption of processed foods and alcohol have been associated with a higher CRC risk. The proportion of CRC attributed to dietary factors has been estimated to be about 50%. Further, approximately 66-77% of CRC cases are believed to be preventable by managing diet and physical activity properly.

In 2007, the World Cancer Research Fund (WCRF) released a report stating that there was convincing evidence of a causal role for red and processed meat, obesity and alcohol in the development of CRC. However, many studies were excluded from the analyses and the role of risk factors such as diabetes and smoking was not explored. This particular study quantified the CRC risk associated with lifestyle and dietary risk factors by updating previous meta-analyses as well as by conducting an overview of the relationship between lifestyle risk factors and CRC risk to highlight possible areas for future intervention. Overall, data from 103 cohort studies on individuals with CRC with information on one or more of these risk factors were included in these analyses.

  • Alcohol consumption - In 9,594 individuals included in these analyses, CRC risk was approximately 60% greater in individuals categorized as heavy drinkers compared with those classed as light or nondrinkers.
  • Diabetes - In 13,637individuals included in these analyses, CRC risk was seen to be 20% higher in individuals with diabetes compared with unaffected individuals.
  • Cigarette smoking- 23,437 individuals met the inclusion criteria for these analyses. Smokers had a 16% greater risk compared with those who had never smoked.
  • Meat consumption- 15,057 individuals were studied to understand the association between meat -either red meat, processed meat, fish and/or poultry - and CRC. There was significant difference in CRC risk between the highest versus the lowest level of consumption of red meat. Similarly, individuals in the highest level compared with those in the lowest level of processed meat intake had a 20%increased risk for developing CRC. Study authors did not observe any association between CRC risk and consumption of either fish or poultry.
  • Fruit and vegetable intake - In 7,956 individuals diagnosed with CRC, there was no evidence of an association between fruit or vegetable intake and CRC risk. However, there was a significant inverse association between fruit intake with rectal cancer but not for colon cancer.
  • Obesity - 57,985individuals with CRC were used to examine the association between obesity and CRC risk. Individuals with a BMI  30 kg/m2 had a 40% greater CRC risk compared with individuals with a BMI of 25 kg/m2.
  • Physical activity- Out of 27,482 individuals with CRC, individuals with high level of physical activity had a 20% lower CRC risk compared with inactive individuals. For colon cancer, the inverse association with physical activity was significantly stronger than for rectal cancer. Further, the protective effect conferred by physical activity was observed to be slightly stronger in men than in women.

Individuals in the top category for alcohol consumption had roughly 60% greater risk for CRC compared with those in the lowest category. Overall, the relationship between CRC risk with high BMI, diabetes, high consumption of red and processed meat and cigarette smoking is broadly the same, with individuals in the highest categories for each of these risk factors having a 20% greater risk of the cancer compared with those in the lowest categories. On the other hand, individuals reporting the highest levels of physical activity had a 20% lower risk when compared with the most sedentary individuals. There was no evidence to support an association between the consumption of fish, poultry, fruit or vegetables with CRC risk.

A previous review had concluded that cigarette smoking over three to four decades is an important risk factor for CRC and should be added to the list of tobacco-associated malignancies. The difference between the previous review and this one - which failed to identify an association between smoking and CRC risk- is likely because of variation in smoking duration, type and amount of cigarettes smoked and the age at which participants began smoking.

The authors of this review did not conduct a specific overview for fiber intake and CRC risk. The Pooling Project of Prospective Studies of Diet and Cancer had previously examined the relationship between dietary fiber and CRC risk in over 8000 cases. They found a protective effect of high fiber intakes of approximately 10-20% -however, this effect was significantly attenuated after adjustment for other dietary and non-dietary risk factors. Their finding conflicts with those from the European Prospective Investigation into Cancer and Nutrition (EPIC), a prospective study from 10 European countries with 1,721 cases of CRC. In EPIC, a significant inverse association of dietary fiber with CRC was observed with significant difference in the relative risk for people in the highest versus the lowest fifth of dietary fiber intake. These variations may arise due to differences in the predominant source of dietary fiber. In EPIC, cereal fiber was reported to confer a greater benefit on risk compared with fiber derived from fruit, vegetables and legumes. This needs to be followed up in future studies.

In conclusion - even small changes in the consumption of alcohol and red and processed meat, weight loss, smoking cessation and increased levels of physical activity can translate into significant reductions in CRC incidence. Taking the best health supplements can also help you achieve optimum health, which is key when trying to prevent all types of cancers. The public health potential would be significant not only for higher-income countries but for many lower-and middle-income countries that are experiencing epidemics of obesity, type-2 diabetes and cigarette smoking and are projected to shoulder a substantial burden of chronic and degenerative disease over the next two decades.

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