Research News
Physical Activity and Cancer
Joyce Hanna, MA, MS, Associate Director, Health Improvement Program
What's the impact of physical activity on cancer - both on the quality of life of cancer survivors and in preventing cancer? The focus on the role of physical activity on cancer has been long overlooked - especially when you compare it to the role of tobacco, alcohol, and diet on cancer. In fact some researchers feel that physical inactivity is more of a risk factor than diet or obesity for cancer. That's why the Centers for Disease Control, American Cancer Society, the National Cancer Institute and American College of Sports Medicine sponsored a conference at the esteemed Cooper Institute of Research in Dallas, Texas on November 5 - 7, 2000 to provide a review of the current literature on the physical activity - cancer relationship. The information from the meeting will help set the stage and focus for physical activity and cancer research for the next decade. It's clear that there are a lot of unanswered questions to provide future directions and recommendations for further research. It was noted that scientists can take advantage of the large volume of research conducted on the role of exercise in the prevention and treatment of other chronic conditions, such as heart disease.
The following is a summary of what was presented and discussed by some of the researchers at the conference. Actually, it was noted many years ago that people who had physically active lifestyles had lower rates of cancer. Some of the most commonly cited mechanisms that support a role of physical activity in preventing cancer are: decreased intestinal transit time, decreased obesity, modulation of reproductive hormone levels, and enhanced immune function.
Avoiding positive energy balance (eating more food than you're burning!)) may be the key to cancer prevention and participating in regular physical activity is a key to avoiding positive energy balance. Where you store your fat and how much, is also related to cancer risk. Storing it in your abdomen area puts you at increased risk. We have a problem right now in our country of an increasing obesity epidemic that goes across gender, age, and race. We're being pushed more and more in our society to eat large portions of energy dense (high calorie) foods while at the same time we have enormous influences to reduce our energy output and become more sedentary. Preventing this positive energy balance should contribute to prevention of some cancers and increased physical activity may be the most important way to do this.
Colon cancer is the most commonly studied cancer in relation to physical activity, with studies showing that active men and women have a 40% risk reduction. Data shows there is no increased risk for colon cancer even if your weight is at an unhealthy level (body mass >index - over 25) if you have high levels of physical activity. Studies show, however, that men (but not women) who have low levels of physical activity with a high body mass index, are at increased risk for colon cancer.
Some studies show a 30% reduction or risk for breast cancer with physically active women, but the data is inconsistent. It appears that lifelong activity is the best protection against breast cancer, and in postmenopausal women, moderate to intense exercise seems to be more clearly associated with risk reduction than low intensity activity. Some data show a risk reduction of 20% for prostate cancer with physical activity, but again the data is inconsistent. The data do not show any association between physical activity and rectal cancer risk. The long latent period of cancer development and the difficulty of measuring levels of activity are two of the greatest challenges that need to be overcome in getting reliable data.
There is much to be done in the area of using physical activity as an intervention with cancer patients and survivors. Studies show that there is less fatigue, less anxiety, better sleep patterns, better body composition, and less depression with patients that are physically active after cancer treatment. The American Cancer Society reported that there are 8.4 million people living with cancer today, including 2,000,000 breast cancer survivors. We are living longer with cancer as a chronic disease and cancer patients not only want a cure, but the ability to live life fully. Physical activity can improve the quality of life and perhaps the quantity of life for people living with cancer.
Interesting Questions that are being studied: How much physical activity, how long, how frequent, how intense, does physical activity have to occur to provide a risk reduction? How do you overcome the difficulty of measuring and standardizing physical activity, especially low levels of intensity, such as gardening, washing the car etc.? Is precise measurements of fitness level necessary (rather than self reports of activity) to understand >better the role sedentary habits in the role of cancer? At what stage in the multiple step process of cancer development is physical activity the most important? When in your life span is it the most important to be physically active? And finally, do the above answers differ for each cancer? Do they differ for men and women? It's going to be exiting to learn more answers to these important issues of physical activity and cancer.
Eating ten servings of fruits and vegetables can help lower biochemical markers of cancer in just two weeks*
Studies have suggested that many components in vegetables and fruits can help reduce breast cancer risk. It is thought that the antioxidants in fruits and vegetables repair the cellular damage that can lead to cancer. A new study sponsored by the American Institute for Cancer Research, sheds light on the biochemical processes behind the protective effect. 28 women, with an average age of 50 years, all at high risk for breast cancer, participated in a pilot study at the AMC Cancer Research Center in Colorado. To boost their antioxidant intake, they all agreed to eat ten or more daily servings of a variety of fruits and vegetables for two weeks. Specific menus and recipes were provided so that the participants could prepare the foods at home. The study was designed to see if a diet high in fruits and vegetables would protect a women's DNA from damage caused by destructive compounds in the body called free radicals. Researchers compared levels of DNA damage when the women entered the study to the levels two weeks after they had adopted the high fruit and vegetables diet. They found that DNA damage had decreased substantially (21 percent) over the two weeks. The study's lead author, cancer researcher Henry Thompson, PhD, stated that the results showed very healthy levels of damage reduction in a remarkable short period of time. The women in the study reported that they felt better, had more energy and had a very good mood level. On the down side some women reported that the preparation of the recipes tedious. While this study can't confirm a protection from breast cancer the results look promising. Dr. Thompson's next steps in a future study are to lengthen the intervention period and find out which families of plants offer the greatest cancer protection and make the diet more convenient to prepare.
* Carcinogenesis, Vol. 2, No 12, Dec. 1999