Recent studies delineate the effect of exercise on specific cancers but much more research on the role exercise plays in the prevention and treatment of cancer is needed, according to Susan Oliveria, ScD, MPH, director of epidemiology at the
Recent studies delineate the effect of exercise on specific cancersbut much more research on the role exercise plays in the prevention andtreatment of cancer is needed, according to Susan Oliveria, ScD, MPH, directorof epidemiology at the Strang Cancer Prevention Center in New York City.Dr. Oliviera addressed the second Strang International Cancer PreventionConference co-sponsored by Cornell University Medical College and heldin New York last November. Preventive efforts are most promising for cancerswhose causes are environmental, she added.
Though the protective role of physical activity in cancer developmentwas hypothesized as early as 1922, the biological mechanisms involved arestill not fully understood, said Dr. Oliveria. However, improved immuneresponse has been observed after moderate exercise, so it may be that anincrease in killer cells (NK and LAK) are partly responsible. Assumptionscan also be made, and in some instances have been confirmed, about thebeneficial effects of exercise on specific cancers. For instance, a recentstudy led by Dr. Inger Thune of the Institute of Community Medicine atthe University of Tromso in Norway found that exercise patterns predictedbreast cancer risk independent of other risk factors. Those who exercisedat least four hours a week had a 37% lower risk of developing breast cancercompared to those who were sedentary. Exercise, the researchers found,reduces the amount of estrogen pumped out by a woman's ovaries and thehypothesis is that the less estrogen a woman is exposed to, the lower herrisk of developing breast cancer. For colon cancer, because physical exercisedecreases gastrointestinal transit time, it may reduce exposure to carcinogensin the gut that contribute to that cancer. Says Dr. Oliveria, "Thereis an observable trend suggesting that the greater the physical activity,the greater the decrease in risk."
Overall, exercise affects energy balance leading to a reduction in bodyfat and weight. Furthermore, Dr. Oliveria said, consistent physical exerciseoften occurs in conjunction with other healthy behaviors that include avoidanceof cigarettes and alcohol, and better nutrition--factors which may decreasecancer risk.
Dr. Oliveria noted that only a few studies have examined the connectionbetween exercise level and specific cancers. The effect of exercise onprostate cancer is still being evaluated. Questions for that cancer rangefrom how long the antitestosterone effect of exercise lasts to whetherthere is a meaningful association between testosterone level and prostatecancer risk. Dr. Oliveria cautions, however, that prostate cancer has along induction period, developing at an age when testosterone levels havealready decreased-- "We may simply be assessing activity level atthe wrong period of life." Studies of the cancer-exercise connectionfor lung, kidney, gastric, brain, testicular cancers, melanoma, Hodgkin'sand non-Hodgkin's lymphomas, and leukemia have been inconclusive.
But another area that Dr. Oliveria believes warrants serious study isthe role of exercise in cancer therapy-- "Can it restrict metastases,prevent recurrence, or be used effectively in the palliative treatmentof established cancers?" Exercise does produce a positive psychologicaleffect on cancer patients, and can inhibit the wasting and lean muscleloss associated with the disease but strenuous exercise could also be detrimental.High-intensity activity decreases the number of killer cells and produceshigher levels of circulating free radicals. Clearly, concluded Dr. Oliveria,further investigation in this area is needed.