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

Colorectalcancer (CRC) is the third most common non-skin cancer and the second leadingcause of cancer-related mortality in men and women in the US and otherdeveloped countries. Approximately 1 million new cases of CRC are diagnosedevery year, and more than half a million people die from this disease, equivalentto approximately 8% of all cancer-related deaths worldwide. Both men and womenhave 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 colonand rectal cancer in the US in 2010 with over 50,000 deaths overall, accordingto the National Cancer Institute.

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

In 2007, theWorld Cancer Research Fund (WCRF) released a report stating that there wasconvincing evidence of a causal role for red and processed meat, obesity andalcohol in the development of CRC. However, many studies were excluded from theanalyses and the role of risk factors such as diabetes and smoking was notexplored. This particular study quantified the CRC risk associated withlifestyle and dietary risk factors by updating previous meta-analyses as wellas by conducting an overview of the relationship between lifestyle risk factorsand CRC risk to highlight possible areas for future intervention. Overall, datafrom 103 cohort studies on individuals with CRC with information on one or moreof these risk factors were included in these analyses.

  • Alcoholconsumption - In 9,594 individuals included in these analyses, CRC risk wasapproximately 60% greater in individuals categorized as heavy drinkers comparedwith those classed as light or nondrinkers.
  • Diabetes - In 13,637individuals included in these analyses, CRC risk was seen to be 20% higher inindividuals with diabetes compared with unaffected individuals.
  • Cigarette smoking- 23,437 individuals met the inclusion criteria for these analyses. Smokers hada 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 asignificant difference in CRC risk between the highest versus the lowest levelof consumption of red meat. Similarly, individuals in the highest levelcompared with those in the lowest level of processed meat intake had a 20%increased risk for developing CRC. Study authors did not observe anyassociation between CRC risk and consumption of either fish or poultry.
  • Fruit andvegetable intake - In 7,956 individuals diagnosed with CRC, there was noevidence of an association between fruit or vegetable intake and CRC risk.However, there was a significant inverse association between fruit intake withrectal cancer but not for colon cancer.
  • Obesity - 57,985individuals with CRC were used to examine the association between obesity and CRCrisk. Individuals with a BMI  30 kg/m2 had a 40% greater CRC risk comparedwith individuals with a BMI of 25 kg/m2.
  • Physical activity- Out of 27,482 individuals with CRC, individuals with high level of physicalactivity had a 20% lower CRC risk compared with inactive individuals. For coloncancer, the inverse association with physical activity was significantlystronger than for rectal cancer. Further, the protective effect conferred byphysical activity was observed to be slightly stronger in men than in women.

Individualsin the top category for alcohol consumption had roughly 60% greater risk forCRC compared with those in the lowest category. Overall, the relationshipbetween CRC risk with high BMI, diabetes, high consumption of red and processedmeat and cigarette smoking is broadly the same, with individuals in the highestcategories for each of these risk factors having a 20% greater risk of thecancer compared with those in the lowest categories. On the other hand, individualsreporting the highest levels of physical activity had a 20% lower risk whencompared with the most sedentary individuals. There was no evidence to supportan association between the consumption of fish, poultry, fruit or vegetableswith CRC risk.

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

The authors ofthis review did not conduct a specific overview for fiber intake and CRC risk. ThePooling Project of Prospective Studies of Diet and Cancer had previously examinedthe relationship between dietary fiber and CRC risk in over 8000 cases. Theyfound a protective effect of high fiber intakes of approximately 10-20% -however, this effect was significantly attenuated after adjustment for otherdietary and non-dietary risk factors. Their finding conflicts with those fromthe European Prospective Investigation into Cancer and Nutrition (EPIC), aprospective 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 asignificant difference in the relative risk for people in the highest versusthe lowest fifth of dietary fiber intake. These variations may arise due todifferences in the predominant source of dietary fiber. In EPIC, cereal fiberwas reported to confer a greater benefit on risk compared with fiber derivedfrom fruit, vegetables and legumes. This needs to be followed up in futurestudies.

Inconclusion - even small changes in the consumption of alcohol and red andprocessed meat, weight loss, smoking cessation and increased levels of physicalactivity can translate into significant reductions in CRC incidence. Taking the best health supplements can also helpyou achieve optimum health, which is key when trying to prevent all types ofcancers. The public health potentialwould be significant not only for higher-income countries but for many lower-and middle-income countries that are experiencing epidemics of obesity, type-2diabetes and cigarette smoking and are projected to shoulder a substantialburden of chronic and degenerative disease over the next two decades.

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