Prostate cancer is the most common internal malignancy in American men; it's second only to lung cancer among the leading causes of male cancer deaths. That makes it an urgent problem, and it is finally getting the scientific respect it deserves. Still, despite thorough investigations that have yielded major advances, many aspects of the disease remain unknown.
One area of uncertainty is the cause of prostate cancer. Genetics certainly play an important role, but heredity cannot explain most cases. Lifestyle factors have also been implicated; the leading candidate is diet. A high consumption of saturated fat from animal sources is linked to an increased risk of prostate cancer, while whole grains, tomatoes, some vegetables, fish, and soy appear protective. Other lifestyle elements that have been linked to the disease include obesity, lack of exercise, and heavy smoking and drinking.
Another area of uncertainty is the best treatment. At one extreme, the evidence favors surgery for men with moderate- to high-grade tumors. At the other extreme, men with low-grade tumors might be best served by watchful waiting. But many men with early, localized prostate cancer fall between these extremes.
Faced with these uncertainties, it is not surprising that up to 73% of men with prostate cancer take nonprescription supplements, and smaller numbers use diet, exercise, or both in the hope of improving their outcome. Most of these men also receive conventional therapy, but a few depend on lifestyle alone.
The appeal of lifestyle therapy is obvious — but does it work? Experts don't know, though a study raises hope that it may have a beneficial impact.
Designing a trial
Scientists from five American research centers joined forces to study lifestyle therapy for prostate cancer. The trial, conducted in San Francisco, was headed by Dr. Dean Ornish, a nutrition expert, and Dr. Peter Carroll, a noted urologist.
One challenge was to design a program that was intensive but sustainable. It included four elements:
Diet. Based on Dr. Ornish's ultra-low-fat vegan diet that is sometimes used for heart disease, the regimen provided less than 10% of calories from fat and contained only trace amounts of cholesterol. The menu consisted mainly of fruits, vegetables, whole grain products, legumes, and soy products.
Supplements. Each man took 58 grams of powdered soy protein, 3 grams of fish oil, 400 IU of vitamin E, 2 grams of vitamin C, and 200 micrograms of selenium every day.
Exercise. The men walked for 30 minutes at a moderate pace six days a week.
Stress reduction. The men performed yoga-based stretching, breathing, meditation, and relaxation exercises for a total of an hour a day.
The trial lasted one year. Three members of the lifestyle treatment group dropped out because the program was too arduous, but none left because they required conventional therapy. Six members of the control group required conventional therapy during the year because of the progression of their disease.
Initially, the treatment and control groups had identical PSA levels. At the end of the year, a small but significant difference was evident. And tests of how the men's blood affected the growth of prostate cancer cells showed similar changes. Blood samples from the lifestyle treatment group inhibited prostate cancer cell growth by 70%, while samples from the control group inhibited growth by only 9%.
The intensive lifestyle study did not answer the $64,000 question: Can this program improve a man's outlook? Since all the men had early-stage, less aggressive tumors, the cancers would be unlikely to grow fast enough to demonstrate clinical differences in just a year. The scientists are continuing to track the men to see if other differences in symptoms or survival emerge over time. After just a year, though, the trends in PSA levels and cancer cell growth inhibition raise hope that lifestyle treatment may prove helpful.
Although the intensive lifestyle trial was careful and scientifically rigorous, it is only one study. But other investigations, though smaller and shorter, tend to support the possibility that lifestyle changes may slow the growth of prostate cancer cells.
A large body of evidence suggests that lifestyle factors have a powerful influence on a man's risk of prostate cancer. Much more research is needed before lifestyle therapy can be recommended clinically. And even if these changes prove beneficial, they will add to but not replace conventional treatment.
Since regular exercise, stress reduction, and a low-fat, high-fiber, plant-based diet are good for general health, they will make a reasonable addition to any prostate cancer program.
Lifestyle therapy or conventional treatment? For prostate cancer, as for so many areas of health, it's not a question of "either/or" but an answer of "both."
August 2007 update