We all know that exercise is an important part of a healthy lifestyle. But more and more evidence shows that regular physical activity is more than just good for your heart and body weight: it can also dramatically reduce your risk of cancer.
In one of the latest studies, researchers from the National Cancer Institute in the US found that exercising five times a week or more was associated with significant reductions in colon and rectal cancer risk. Interestingly, it wasn't only the vigorous exercisers who benefited, but those who could only manage moderate- and low-intensity physical activity, too. Conversely, more time spent doing sedentary activities, such as watching TV, was associated with an increased risk of colon cancer (Cancer Causes Control, 2008; Apr 25; Epub ahead of print).
The study is another addition to the consistent and convincing body of evidence showing that exercise plays a key role in colon-cancer prevention. Indeed, according to one review, physical activity is not merely a marker of a healthier lifestyle, but it has an independent protective effect. On average, the cancer-risk reduction is 40-50 per cent, and reductions up to 70 per cent have been seen in some studies (Cancer Epidemiol Biomarkers Prev, 2001; 10: 287-301). It appears that the more exercise the better, although even just one hour of walking a week can protect against the disease (Int J Cancer, 2007; 121: 2776-81).
There is also strong evidence for a positive effect of physical activity against breast cancer. Here again, studies have observed up to a 70-per-cent reduced risk among those who are most active in their occupational and/or recreational activities. How-ever, a certain level of activity may be needed to invoke a protective effect, and the effect may vary among particular subgroups of women (Cancer Epidemiol Biomarkers Prev, 2001; 10: 287-301).
Indeed, in one study, researchers found a significantly reduced risk of invasive breast cancer only for women who were physically active for six hours or more per week. They also observed that this risk reduction was limited to women without a first-degree family history of breast cancer (Cancer Epidemiol Biomarkers Prev, 2007; 16: 236-43). Nevertheless, other studies have reported a beneficial effect with lesser amounts of exercise. And some show a reduced risk even for women with a family history of the disease (Cancer Epidemiol Biomarkers Prev, 2006; 15: 57-64).
Breast-cancer studies also show that exercise can improve the chances of survival after the diagnosis. An analysis of nearly 3000 women found that those who engaged in physical activity equivalent to walking one hour per week or more had better survival rates compared with those who exercised less than that or not at all. Women who walked three to five hours a week had the lowest risk of death from their breast cancer, but there was little evidence of any further benefit with more exercise than this (JAMA, 2005; 293: 2479-86).
Breast-cancer patients who exercise also have better mood, better body image and better self-esteem, and an improved quality of life (CA Cancer J Clin, 2005; 55: 265-6; JAMA, 2005; 293: 2479-86).
Other types of cancer that appear to be related to exercise include prostate, and endometrial and lung cancers. Regular exercise can reduce the risk of developing these diseases by up to 40 per cent (J Nutr, 2002; 132: 3456S-64S).
So how does exercise help to fight against cancer? Exercise can reduce obesity, which predisposes to several types of cancer. It can also change the body's hormone levels, which may have a beneficial effect. Finally, physical activity may improve immune function. However, the likelihood is that several, interrelated actions are involved (J Nutr, 2002; 132: 3456S-64S).
Although more research is needed on the subject, what is clear is that exercise should be recommended to everyone as a simple, natural way to reduce the risk of cancer as well as other diseases. A number of public health organizations now recommend at least 30 minutes of moderate-to-vigorous exercise on most days of the week for cancer prevention.
Other benefits of exercise
- Lower rates of heart disease (N Engl J Med, 2002; 347: 716-25; JAMA, 1995; 273: 1093-8)
- Reduced risk of stroke (JAMA, 2000; 283: 2961-7)
- Better mental health (Br J Sports Med, April 2008; doi:10.1136/bjsm.2008.046243)
- Enhanced cognitive (executive-control) function (Psychol Sci, 2003; 14: 125-30)
- Reduced risk of falls and related injuries such as bone fractures (BMJ, 1997; 315: 1065-9)
- Better blood pressure control (J Clin Epidemiol, 1992; 45: 439-47)
- Better glucose control in type 2 diabetics (JAMA, 1999; 282: 1433-9)
- Reduced joint swelling in older people with knee osteoarthritis (JAMA, 1997; 277: 25-31)
- Lowered likelihood of gallstone disease (N Engl J Med, 1999; 341: 777-84)
- Better quality of sleep (Sleep, 2003; 26: 830-6; JAMA, 1997; 277: 32-7).