THE RISE OF COLORECTAL CANCER IN ASIA IS UNMISTAKABLY LINKED TO ECONOMIC progress and developed world standard of living. It is obvious that changes in lifestyle, including diet, are important but it is difficult to prove because colorectal cancer is a complex disease arising from decades of intricate interactions between gene, age and lifestyle.
Colorectal cancer is a disease spectrum, not a single entity. When a 20 to 30 year-old develops cancer, which is rare, accounting for only three percent of all colorectal cancers, the cause is an inherited mutation of either the Polyposis or Hereditary Non-Polyposis Colorectal Cancer genes, lifestyle plays little role. When a 90 year-old develops cancer, it is due to age and accumulated deleterious lifestyle factors, genetic profile plays little role. However, the majority of colorectal cancers occur between 45 to 75 years of age, they develop from years of interactions between genetic and lifestyle factors.
Normal growth and death of cells are exquisitely controlled by genetic pathways and loss of control can lead to cancer. One of the key pathways is the Transforming Growth Factor-β Signaling Pathway (TGF-β). Its stability is delicately maintained by a cascade of genes. Some have variants which are more fragile and are more susceptible to damage by lifestyle factors leading to instability of the signaling pathway and cancer. Sixteen such genes have been identified and they can be detected from a blood test. Each person can have his or her genetic risk determined and grouped into low, moderate or high according to normal, one to two fold or three or more fold increase.
It is well recognised that diet high in red and processed meat, low in fruits, vegetables and fibre, lack of exercise, obesity, diabetes and smoking are risk factors for colorectal cancer while Aspirin, other Non-Steroidal Anti-Inflammatory Drugs (NSAIDs) and estrogen are protective factors. There is a questionnaire to calculate individual risk for developing colorectal cancer according to the composite score of harmful or protective lifestyle factors, not unlike the risk assessments for heart diseases and stroke of life insurance companies. Again, there are three levels of risk.
The most exciting breakthrough in colorectal cancer research is the confirmation that lifestyle factors can and do modulate genetic risk. When a person is born with a high genetic risk and he or she has high lifestyle risk, the resultant risk is greater than the sum of total ie. eight or more folds increase in risk instead of six. |
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Conversely when a person has a low genetic risk and low lifestyle risk, the overall risk is significantly reduced. Unfortunately, when a person has a high genetic risk, adopting a healthy lifestyle will not reduce his or her genetic risk from high to moderate or low, but it does prevent it from getting any higher. It is important to remember that a healthy lifestyle is not only protective against colorectal cancer but against breast and other cancers, heart disease and stroke as well.
Although diet is only one of the many lifestyle factors associated with colorectal cancer, it is the most talked-about and misunderstood because of cultural beliefs, myths and media hype. It is not uncommon for patients to exclaim: “How is it possible for me to get colorectal cancer when I drink bitter gourd or beetroot juice everyday; take the most expensive vitamins, antioxidants and immune-boosting supplements; avoid all “poison possessing” foods like chicken, duck or prawn; consume only organic food or am a vegetarian?” It is only after years of painstaking research that we are confident eating more than half a kilogram of red or processed meat (ham, bacon and sausages) a week is harmful and eating more fish and dietary fibre is protective. For many years, the association of dietary fibre and colorectal cancer had been confusing. It is now evident that unprocessed fibre, especially from cereals and whole grains, which still contains a natural balance of vitamins, minerals, antioxidants and many more compounds which are still unknown to us, that is beneficial. These nutrients are lost in processed fibre which explains why past studies had been equivocal. It also explains why bottled vitamins, minerals and supplements do not prevent colorectal cancer when tested on normal populations.
On the contrary, there is increasing evidence that such supplements can cause harm. Excess folic acid causes more colorectal cancer in individuals with colorectal polyps and vitamins A and E cause more lung cancers in smokers. This is understandable because cancer or pre-cancer cells grow faster than normal cells, so they require more nutrients. In normal healthy individuals, excess nutrients from supplements are simply excreted in the urine and faeces but in individuals with dysfunctional growth pathways, abnormal cells are stimulated to grow even faster turning them into cancer. It is like pouring fertilisers onto weeds. It is just common sense that the nourishments from fresh fruits, vegetables, cereals and grains as provided by Nature can never be duplicated or supplanted by man.
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