Colorectal cancer is an extremely common and often fatal form of cancer. In the United States, it is the fourth most common type of cancer and is second only to lung cancer in terms of mortality with almost 52,000 deaths in the USA alone last year. The lifetime risk of developing colorectal cancer for a 30 year old living in the United States today is 5.24%. Although great advances have been made in recent years in the early detection and treatment of colorectal cancer, the 5-year survival rate from diagnosis is only 65%, much lower than the survival rates for some other common types of cancer such as breast, skin, and prostate cancer.
The good news is that colorectal cancer is considered one of the most preventable forms of cancer. It is estimated that 60-85% of colorectal cancers are a result of poor lifestyle and dietary choices. Here are eight of the most significant modifiable risk factors for colorectal cancer.
1: Regular physical exercise is consistently shown to decrease the risk of developing colorectal cancer. Individuals with the highest levels of physical activity (at least 30 minutes a day, 3 days a week of strenuous exercise) typically show a reduction of 30 to 40% in the risk of developing colorectal cancer compared to those who engage in little of no exercise.
2: Smoking status is a significant risk factor for colorectal cancer. A study, published in 2000 using data from the Cancer Prevention Study II, found that smoking increased the risk of developing colorectal cancer by 32% and 41% for men and women respectively. The study concluded that over 12% of all colorectal cancer deaths were attributable to smoking.
3: Regular aspirin use has been found to reduce the risk of developing colorectal cancer in numerous studies. One such study, published in the New England Journal of Medicine in 1991, found a 40% reduction in colorectal cancer in men and a 42% reduction in women for those who used aspirin 16 or more times a month.
A more recent study, published in The Lancet last year, used the results of two randomized control trials to determine the effects of low dose aspirin on the risk of developing various types of cancer. The researchers found that the 20 year risk of death from colorectal cancer was 40% lower in the aspirin group compared to the group who received a placebo. Aspirin also appeared to reduce the risk of other forms of cancer including pancreatic, lung, stomach, and prostate. Daily aspirin intake should be kept to between 80mg and 125mg and should not be taken if you have a history of stomach ulcers or gastric bleeding.
4: Dairy products appear to offer a modest degree of protection against colorectal cancer. This is believed to be due to a combination of the calcium and vitamin D present in most dairy products. Low-fat milk appears to be the most effective at reducing colorectal cancer risk.
5: High consumption of red and processed meats appears to be a risk factor for colorectal cancer. One of the largest and well known studies on the issue of red meat and cancer was published in the journal PloS Medicine in 2007 and involved 500,000 people aged between 50 and 71. That study found that individuals in the top 20% for red meat consumption were 24% more likely to develop colorectal cancer than those in the bottom 20%. The risk appears to be greatest when meat is cooked at a very high temperature such as pan frying or barbecuing as this generates greater levels of compounds called heterocyclic amines (HCA’s) which are carcinogenic to humans.
6: Overweight adults are more likely to develop colorectal cancer than normal or underweight adults. The risk of colorectal cancer is about 75% greater in men and 25% greater in women when BMI is greater than 30 compared to those in the normal weight range. The graph to the right shows the risk of colorectal cancer across different BMI ranges as calculated in a study published in the American Journal of Epidemiology in 2000 involving more than 850,000 men and women from the Cancer Prevention Study II. It is believed that insulin or insulin-like growth factors that are present in high levels in obese people may promote colon cancer development.
7: Vitamin D levels appear to be inversely related to the risk of colorectal cancer. According to a study published in the American Journal of Preventative Medicine those with the highest levels of vitamin D were around half as likely to develop colorectal cancer as those with the lowest vitamin D levels. The researchers concluded that daily intake of between 1000 and 2000 IU/day of vitamin D3 would reduce the incidence of colorectal cancer with few adverse effects.
8: Alcohol consumption appears to increase the risk of colorectal cancer although increased risk only appears at relatively high levels of alcohol consumption. This study suggested an increased risk of colorectal cancer of 16% for people consuming between two and three standard drinks of alcohol a day and 41% for people consuming more than three standard drinks a day.
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