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“A critical weekly review of important new research findings for health-conscious readers”
EXERCISE & PROSTATE CANCER RISK
There is an increasing body of research evidence to suggest that many cases of cancer can be prevented through lifestyle and diet modifications. Indeed, even conservative estimates suggest that more than 60 percent of new cancer cases could be prevented simply by abstaining from unhealthy lifestyle and dietary habits. (More enthusiastic cancer prevention experts have suggested that 80 percent of cancer cases, or more, might be preventable with rigorous lifestyle and diet changes.) Given that, in the best case, modern cancer treatment results in the long-term survival of only about 60 percent of all cancer patients, and that the survival rate for many of the most lethal cancers still remains far more dismal, an ounce of cancer prevention is certainly worth much more than a pound of cancer cure. (This simple yet profound realization is the central theme of my new book, “A Cancer Prevention Guide for the Human Race,” which will be published in the spring of 2010.)
As a practicing comprehensive Surgical Oncologist, I routinely treat patients with highly lethal cancers, many of which are, sadly, incurable by the time they are diagnosed. While not every case of cancer can be prevented through lifestyle and diet modification, many of the terrible, and ultimately fatal, cancer cases that I routinely see might have been prevented with reasonably moderate alterations in the way that people choose to live their daily lives.
Prostate cancer is the most common non-skin cancer that occurs in men, and the second most common cause of cancer death in men. In 2009, an estimated 192,000 new cases of prostate cancer will be diagnosed, and approximately 27,000 men will die of this disease. Prostate cancer currently afflicts 1 out of every 6 American men during their lifetimes, and accounts for 25 percent of all cancer diagnoses in men (similar, I might add, to the percentage of breast cancer cases among all cancer cases diagnosed in women). Most prostate cancers are stimulated to grow and spread by testosterone and other androgens produced by the testes, and by other tissues in the body.
The relationship between prostate cancer risk and exercise has not been entirely clear, thus far, as various clinical studies have produced contradictory findings. Some of these studies have suggested that high levels of daily physical activity may reduce the risk of prostate cancer, while other studies have not confirmed a link between prostate cancer risk and physical activity levels.
A new prospective public health study, just published in the British Journal of Cancer, adds further important evidence that increased levels of physical activity may indeed reduce the risk of developing prostate cancer. In this newly published study, nearly 46,000 men between the ages of 45 and 70 years were prospectively followed between 1998 and 2007. All of these male volunteers completed extensive questionnaires regarding their daily levels of physical activities at 30 years of age and at 50 years of age, as well as at the time or their entry into this clinical study. These questionnaires specifically included questions regarding walking or bicycling; current waist, hip and height measurements; education level; cigarette smoking; alcohol consumption; diabetes; family history of prostate cancer; and other lifestyle factors. Six predefined activity levels for occupational activity (from “mostly sitting down” to “heavy manual labor”), and additional predefined categories for time spent on different activities, were specifically included in the questionnaire, such as walking or bicycling (“hardly ever” to “more than 90 min per day”), home or household work (“less than 1 hour per day” to “more than 8 hours per day”), inactive leisure time (“from 2 hours per day or less” to “5 hours per day or more”), and active leisure-time exercising (“from less than 1 hour per week” to “more than 5 hours per week”). The patient volunteers were also queried regarding the average number of hours per day they spent sleeping.
Importantly, the researchers conducting this study took the extra step of conducting 7-day physical activity evaluations to verify that the study’s participants actually engaged in the levels of physically activity that they claimed on the questionnaires. (This additional validation step confirmed the accuracy of the questionnaire information supplied by the study’s volunteers.) The incidence of prostate cancer, and the death rate associated with prostate cancer, among these 45,887 middle-aged and elderly men were then analyzed at the conclusion of this very large prospective epidemiological study.
When the men who engaged in physical activity at the highest levels were compared with those at the lowest levels, some very important differences in prostate cancer risk emerged. Overall, very high levels of physical activity were associated with a 16 percent reduction in the risk of developing prostate cancer. Additionally, among the men who spent at least half of their work days being physically active, the risk of prostate cancer was 20 percent lower when compared to men who spent most of their work day sitting down. Specifically, and very importantly, there appeared to be a linear and progressive decrease in prostate cancer risk with each additional 30 minutes of walking or bicycling per day over the course of the adult lifetimes of these men (this linear relationship was noted within a range of 30 to 120 minutes of walking or bicycling per day). Additionally, the risk of developing advanced prostate cancer appeared to be further lessened by regular daily physical activity.
The results of this study mirror those of other high-quality cancer prevention studies for other types of cancer (including, most notably, breast cancer). While clinical research studies such as this one are prone to various forms of bias, and in particular, biases that arise from patients “self-reporting” their personal health and lifestyle information on study questionnaires, the authors of this study appear to have taken very significant and effective steps to reduce the risk of including such biases in the data that they collected from these nearly 46,000 men. Therefore, although a small degree of residual error cannot be completely excluded from the results of this impressive epidemiological study, its findings that progressively higher levels of daily physical activity (and, it must be stressed, throughout one’s lifetime) are associated with a decreasing level of prostate cancer risk are very likely to be valid even in the presence of small errors in the study’s data (if they exist).
Cardiovascular disease remains the most common cause of premature death in most societies. Cancer is the number two cause of premature death when including people of all ages, and the number one cause of premature death below the age of 80 in the United States. Regular exercise, including relatively moderate activities such as brisk walking or bicycling, have been shown to significantly reduce the risk of death due to cardiovascular disease, as well as, increasingly, the risk of developing or dying from multiple different types of cancer. Based upon the results of this well designed and well executed prospective clinical research study, it would appear that prostate cancer can be added to the list of life-threatening illnesses for which the risk can be decreased through regular and frequent physical activity (and both at work and at home).
Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity
Dr. Wascher is an oncologic surgeon, a professor of surgery, a cancer researcher, an oncology consultant, and a widely published author