Abstract
Early detection of cancer through screening is an important step in decreasing both morbidity and mortality. Likewise, specific modifiable lifestyle behaviors are associated with reduced risk of colorectal cancer. Lifestyle practices have also been shown to maximize health after the primary treatment of cancer. Both these roles for lifestyle interventions are discussed.
Colorectal cancer is the third leading cause of cancer related deaths. 1 Every year approximately 1 million people worldwide are diagnosed with colorectal cancer and more than half a million people die annually from this disease. 2 While secondary prevention through screening is the leading method of addressing colorectal cancer, there is strong evidence to suggest that a combination of screening and primary prevention through lifestyle modification will help reduce the prevalence of colorectal cancer. 3 Because an in-depth review of the screening of colorectal cancer is provided in this issue by Diaz and Slomka, 4 we will focus on the primary prevention.
Primary prevention involves an intervention that is applied to a healthy population of people 5 and addresses lifestyle behaviors that can be modified to reduce future risk of disease development. 6 These lifestyle behaviors often include diet, sleep, and exercise. Research has shown that not only do these lifestyle behaviors assist with prevention of cancer, but they also assist with improving the long-term outcomes of cancer survivors. 7
Modifiable Risk Factors
Several lifestyle factors are associated with an increased incidence of colon cancer. One of the strongest lifestyle risk factors associated with this cancer is body mass index. 8 The International Agency for Research on Cancer concluded that 11% of colon cancer cases were caused by obesity. 9 Growing evidence suggests that insulin is the pathway for this relationship. 10 Specifically, hyperinsulinemia may be a critical factor associated with development or progression of colon cancer.11-15 The association between cancer and obesity is stronger in men than in women. 16
Primary prevention involves an intervention that is applied to a healthy population of people and addresses lifestyle behaviors that can be modified to reduce future risk of disease development.
Whereas obesity is a risk factor, physical activity appears to be a protective factor for colon cancer. 17 There is consistent evidence that higher levels of physical activity are associated with a risk reduction for colorectal cancer,17,18 and it is unlikely that this strong inverse relationship is confounded by other lifestyle factors. 19 Although it was originally thought that physical activity improved the mobility of the colon, decreasing the exposure of the colon to toxins, more recent data suggest that this reduction is more likely associated with improved body weight 18 and a reduction in chronic inflammation. 20
Although the role that energy balance plays in the incidence of colon cancer is fairly clear, the mechanisms behind these lifestyle factors are in need of further investigation. To identify possible mechanisms, several dietary factors have been examined and appear to be associated with colon cancer. However, it is important to note that the following dietary factors have yet to be studied independently from energy intake, and the results from studies in this area are often inconsistent.21-24 The consumption of citrus fruits 25 and dark green vegetables 26 appear to protect against colorectal adenoma, a precursor for colorectal carcinoma. Fiber may have a protective effect as well. 27 Additionally, the consumption of red and processed meat appears to increase the risk for colorectal cancer.21,28 However, this risk may be due mostly to cooking these meats at high temperatures. 29
The relationship between increased rates of colon cancer and obesity in Westernized countries lends further support to the link between energy imbalance and cancer. Not only are rates of colon cancer significantly higher in economically developed countries, there are large increases in the incidence of colon cancer for groups that have moved from less Westernized to more Westernized areas. Based on this type of information, it has been estimated that as much as 90% of colon cancer cases have a primarily lifestyle contribution. 30
Lifestyle Intervention After Primary Treatment for Cancer
With improvements made in the early detection and treatment of cancer, the number of cancer survivors is increasing. 31 These individuals have been shown to have distinct needs in terms of health care. 32 For example, cancer survivors are more likely than the general public to develop cardiovascular disease and diabetes.32,33 Common lifestyle factors such as not practicing a healthy diet and lack of exercise have been identified as possible reasons that cancer patients are more likely to die from noncancer causes. 33 In fact, the US Institute of Medicine has recommended that lifestyle intervention should be an area of focus for this high-risk population. 7
The need for improvements in diet is most clear for cancer survivors who are overweight or obese. Because increased body weight has been associated with increased risk of recurrence of colon 34 and other cancers, 35 the American Cancer Society recommends that modest weight loss should be encouraged for overweight and obese cancer survivors through a balanced diet. 36 These American Cancer Society guidelines also recommend that weight losses of 5% to 10% should be the goal as this degree of weight loss has been associated with improved outcomes in noncancer samples. 36
Although physical activity plays a role in energy balance, it has also been shown to improve the quality of life in survivors of colon cancer. In a physical activity trial of colon cancer survivors, those with increased fitness had the highest quality of life scores after a physical activity intervention. 37 Although this study had several methodological issues including contamination, it was noted that these cancer survivors were highly likely to engage in exercise with 51.6% of the control group participating and 75.8% of the treatment group participating in exercise 3 to 5 times per week. This is consistent with other literature that cancer survivors are motivated for behavior change. 38
Summary
There is evidence to suggest that primary prevention efforts in the general population will help further reduce rates of colorectal cancer. Because obesity has been shown to be a risk factor for developing colorectal cancer, primary prevention efforts have focused on the modification of lifestyle behaviors (ie, diet and physical activity). Eating a diet rich in fruits and vegetables, low in fat, and high in fiber appears to be beneficial for colorectal health. Although it was beyond the scope of this review, other lifestyle behaviors such as excessive consumption of alcohol and cigarette smoking have also been shown to be related to colorectal cancer and have become the focus of primary prevention as well. 39 Risk for colon cancer could be reduced by as much as 71% through the modification of lifestyle factors. 40 Efforts are being made to increase public awareness and adherence to lifestyle behaviors that may help prevent not only colorectal cancer but also other health problems such as diabetes and heart disease. While early detection is most clearly related to improved survival rates, a combination of appropriate screening and lifestyle modifications will help both prevent colorectal cancer and improve outcomes for cancer survivors.