April 14, 2009 In August 2008, University of Michigan's Dr. Mark Moyad, specialist in complementary and preventative medicine, delivered a highly entertaining talk at the National Conference in Calgary. (He returned to the 2009 conference.)
The title of his presentation, "Dietary supplements from A-Z, What Works and What's Worthless," speaks directly to the frustration men with prostate cancer experience when trying to make decisions about complementary therapies. We all have a fairly good general idea of which foods and lifestyle choices are good for us and which are not. But other complementary therapies for prostate cancer seem to fall in and out of favour, leaving us befuddled. So we’ve undertaken to summarize the current research. Which vitamins and other supplements do work, which are worthless, and which do we not know enough about to judge? Here is the state of the evidence.
Selenium and Vitamin E In January 2009, the Selenium and Vitamin E Cancer Prevention Trial (SELECT) reported that neither selenium nor vitamin E prevented prostate cancer when given at the tested doses and formulations to healthy men. The trial randomly assigned the 35,533 participating men into one of 4 groups: one group received selenium, another vitamin E, a third both supplements, and a fourth a placebo. Men in the trial were told to stop taking their supplements in the fall of 2008, when an early look at the data showed no benefit. Researchers speculated that these results might be a consequence of the form of vitamin E used and the high dosage.
"I am afraid it will be the end of the story for large trials of vitamin E and selenium to prevent prostate cancer," says Dr. Edward Messing, SELECT study investigator. "For vitamin E, that is unfortunate. Probably if given in a more effective form, it would be a protective or even therapeutic agent."
As for selenium, its beneficial effects had previously been seen only in men who had low levels of this essential trace element in their blood. There was even evidence that people with higher levels increased their risk of certain types of skin cancer if they took selenium at some doses over the long term. "This is just another example of the importance of treating supplements like medications, which have a window of dosage effectiveness and potential for deleterious results beyond the normal range of intake," advises an article on the urologist's role in informing patients of complementary and alternative therapies useful in combating prostate disease. (See this article.)
Some smaller trials involving selenium, vitamin E, and other antioxidants are ongoing. Two of these are based in Toronto, and both are headed up by Dr. Neil Fleshner, the inaugural holder of the Love Chair in Prostate Cancer Prevention at the Princess Margaret Hospital:
Study of Antioxidants on MRI Detectable Early Stage Prostate Cancer Among Men on Active Surveillance
Study of Antioxidants on Prostate Tumours in Men Undergoing Radical Prostatectomy for Prostate Cancer
Vitamin D and Calcitriol For years, researchers have suspected that insufficient vitamin D production and intake are connected to a higher risk of prostate cancer. One reason for this suspicion is that prostate cancer is more common in sun-starved northern countries and among men of African descent. Sunlight can promote the synthesis of cholecalciferol (vitamin D3) in the skin, and those with dark skin make less than those with light skin when exposed to the same amount of sunlight. (See our web page "Who is at risk for developing prostate cancer?")
Recent research, however, often reports contradictory findings about the effects of vitamin D on prostate cancer. Nevertheless, ASCENT, a trial studying the effects of calcitriol in men with androgen-independent prostate cancer had positive results. Calcitriol, a synthetic physiologically active form of vitamin D, was given in high doses to men receiving docetaxel chemotherapy to treat hormone-refractory prostate cancer. The calcitriol group had a reduction in PSA levels and longer chemotherapy "holidays." Moreover, the combination of docetaxel and calcitriol seemed to improve overall survival and to have a favourable safety profile when compared to chemotherapy alone, but further studies are needed.
A small British study published in January 2009 reported that elevated serum levels of vitamin D could be associated with a reduced risk of death from prostate cancer. In this study of 160 prostate cancer patients, those with medium and high levels of 25-hydroxyvitamin D (calcidiol) were at 67% and 84% decreased risk of death than those men who had a low level.
The Canadian Cancer society recommends that adults living in Canada consider taking a vitamin D supplement of 1,000 international units each day, at least during the fall and winter. Older Canadians or those who don't get much exposure to the sun should consider taking this amount all year round every day.
Always consult your physician, though. And, if you are fighting prostate cancer, supplementation should be based on need, so ask your physician about a blood test to check serum levels of vitamin D.
Lycopene This antioxidant, which is derived mainly from tomatoes, has been studied widely to assess its benefits for men with prostate cancer. Again, results are mixed. Two studies reported positive results, a reduction in PSA levels among those taking lycopene (4 mg) and a significant decrease in PSA doubling time (PSADT or the time it takes PSA levels to double --- the longer the better!) Other studies, however, have found no statistically significant benefit from lycopene. Clinical trials are still underway. (See a list of these.)
Pomegranate juice This juice is considered an antioxidant because it seems to help prevent or slow oxidative damage to cells. It also appears to protect against atherosclerosis --- the narrowing of the arteries. Some studies suggest that pomegranate juice inhibits prostate tumour growth (in a test tube not in a man) and lowers or slows the rate of increase in PSA levels. (See list of clinical trials.)
Soy and phytoestrogens A few studies have looked at using soy supplements as a complementary therapy for men with prostate cancer. Usually, soy isoflavones are taken along with other agents. One study, conducted in Europe in 2005, found that a supplement of soy, isoflavones, lycopene, silymarin, and antioxidants, when given to men with rising PSA who had been treated for prostate cancer, delayed PSA progression significantly. Other research has found no significant benefit. Still, research continues. A 2009 study suggests that prostate tissue may have the ability to concentrate dietary soy isoflavones to potentially anti-carcinogenic levels.
So there you have a snapshot of the research to date. To learn more, read Dr. Moyad’s comprehensive guide The ABC's of Nutrition and Supplements for Prostate Cancer.