MANCHESTER, UNITED KINGDOM. Men face a much more dangerous form of prostate cancer if tumor cells from the prostate gland metastasize and migrate and invade other parts of the body, such as bone marrow. New research suggests that oily fish may help prevent this process. It appears that omega-3 fats contained in oily fish can prevent the cancer spreading to bone marrow, a process which may be encouraged by the other major group of polyunsaturated fatty acids – omega-6 fats. Researchers at the Christie Hospital in Manchester found evidence for this effect in laboratory tests, where they showed that omega-3 fats can inhibit invasion by prostate cancer cells, potentially reducing the threat of metastasis. They also found that omega-6 fatty acids, found in vegetable oils, nuts and seeds, increased the risk of tumor cells spreading into bone marrow. This invasion was blocked by omega-3 fats, which are found in oily fish such as salmon, mackerel and tuna. The researchers believe that cancerous tumors may use omega 6 fats as a high-energy food, enabling rapid growth. Omega-3 fats are known to interfere with the various functions of omega-6 fats, they explain, and this was confirmed by the current findings. This effectively removes the cancer’s ‘free lunch’, a fact that may have clinical importance. Eating a diet with the right balance of omega-3 and omega-6 fats may well help to keep prostate cancer within the prostate gland where it may be monitored safely or more easily treated with surgery or radiotherapy, they conclude, adding that a healthy balance of these two types of fat would be about half as much omega-3 as omega-6. Many cancers, including breast and prostate cancer, seem to invade bone marrow rather than other parts of the body. If it could be shown that this is influenced by the proportion of different types of fat, then scientists may be able to develop drugs that prevent metastasis.
Brown, M.D. et al. Promotion of prostatic metastatic migration towards human bone marrow stoma by Omega 6 and its inhibition by Omega 3 PUFAs. British Journal of Cancer, Vol. 94, March 27, 2006. pp. 842-53

Design of the SELECT trial
HOUSTON, TEXAS. It is estimated that 230,000 American men will be diagnosed with prostate cancer and that 30,000 men will die from the disease in 2004. There are currently no pharmaceutical drugs that have been proven effective in preventing prostate cancer. Finasteride (Proscar) showed some promise in reducing overall cancer incidence but was, unfortunately, associated with a significant increase in advanced cancers. Finasteride is therefore no longer considered suitable for prostate cancer prevention. In contrast, two natural agents, selenium and vitamin E, have been found effective in prostate cancer prevention. The Nutritional Prevention of Cancer (NPC) study concluded that supplementing with 200 micrograms/day of elemental selenium (in the form of high-selenium yeast) reduced prostate cancer risk by 63%. The large Finnish ATBC study concluded that supplementing with 50 mg/day (50 IU/day) of synthetic alpha-tocopheryl-acetate reduced prostate cancer risk and mortality by 32% and 41% respectively.

Based on these and other findings, the National Cancer Institute has embarked upon a major trial, the Selenium and Vitamin E Cancer Prevention Trial (SELECT). The trial, opened for recruitment in July 2001, now has a total enrollment of 35,534 men with a median age of 62 years (range of 50-93 years) who were free of prostate cancer. The expected follow-up time is 7-12 years. After much deliberation and a thorough review of the literature, the SELECT Steering Committee decided that the supplements to be evaluated would be 200 micrograms/day of elemental selenium in the form of L-selenomethionine and 400 IU/day of synthetic alpha-tocopheryl acetate. The trial design will involve 5 pair-wise comparisons of prostate cancer incidence, in association with – vitamin E vs placebo, selenium vs placebo, vitamin E plus selenium (combination) vs placebo, combination vs vitamin E, and combination vs selenium. The Steering Committee points out that there is strong evidence that 200 micrograms/day of elemental selenium is entirely safe, as is up to 1000 mg/day of vitamin E. They acknowledge that natural alpha-tocopherol is significantly more effective than synthetic alpha-tocopheryl acetate and that gamma-tocopherol may be even more effective than either as far as prostate cancer prevention is concerned. However, due to the fact that more clinical trial data is available on synthetic alpha-tocopheryl acetate they decided to go ahead with this form. All study participants will also receive a daily multivitamin devoid of selenium and vitamin E, but including 400 IU of vitamin D3.
Lippman, SM, et al. Designing the Selenium and Vitamin E Cancer Prevention Trial (SELECT). Journal of the National Cancer Institute, Vol. 97, January 19, 2005, pp. 94-102

Editor’s comment: It is indeed gratifying to see such a massive undertaking by the National Cancer Institute aimed at evaluating natural supplements in the prevention of prostate cancer. Personally, I would have liked to see the vitamin E component consist of a 50:50 mixture of natural alpha- and gamma-tocopherols, but the Steering Committee obviously decided that there was not enough evidence to support this. In any case, involving over 35,000 men in a 7- to 12-year trial of selenium and vitamin E clearly shows that hopes are high that these two natural compounds will prove effective in prostate cancer prevention and that they are entirely safe. In view of this, I see no reason to wait 10 or more years for the results to be published. All men should supplement with selenomethionine and natural vitamin E (preferably a 50:50 mixture of alpha- and gamma-tocopherols).

Diabetes protects against prostate cancer

ATLANTA, GEORGIA. The possible protective effect of diabetes against prostate cancer has been investigated once more, this time in a prospective study. Earlier studies have shown a reduction in risk of 10 to 40 per cent, and some suggest that diabetes is protective only several years after diagnosis. Researchers from the American Cancer Society used data on a group of 72,670 men from the Cancer Prevention Study II Nutrition Cohort. Information on diabetes and prostate cancer was gathered in 1982, 1992, 1997, 1999 and 2001. Prostate cancer was diagnosed in 5,318 men (7.3 per cent), who tended to be older and with a higher BMI.

The researchers found that overall; diabetes reduced the risk of prostate cancer by 33 per cent once age, race, education and prostate-specific antigen testing were taken into account. However, risk was significantly increased (by 23 per cent) in the first three years after diabetes diagnosis, compared with non- diabetic men, and only began to be protective after four years. The protective effect remained consistent when stage or grade of prostate cancer at diagnosis was examined. These results are consistent with the hypothesis that diabetes is associated with reduced risk of prostate cancer but only several years after diagnosis of diabetes, say the authors. The protective effect may be due to the reduced insulin levels found in men who have been diabetic for some time, as prostate cancer has been linked to high circulating levels of insulin.

The findings in the present study are consistent with results from a Health Professionals Follow-up Study, which also found an increased risk following diagnosis of diabetes and a protective effect after several years. In this study, prostate cancer risk was lowest 10 years after diabetes diagnosis, a reduction of 46 per cent. On the other hand, a recent case-control study within the US Physicians’ Health Study found a reduction in risk of 36 per cent, but with no link to the time since diabetes diagnosis.
Rodriguez, C et al. Diabetes and Risk of Prostate Cancer in a Prospective Cohort of US Men. American Journal of Epidemiology, Vol. 161, January 2005, pp. 147-152

Fish oils help prevent prostate cancer

BETHESDA, MARYLAND. Alpha-linolenic acid (ALA) is a major component of flax seed oil and has been associated with significant cardiovascular benefits. Some studies, however, have shown that a high intake of ALA is associated with an increased risk of prostate cancer. A prestigious team of researchers from the National Cancer Institute, the Harvard Medical School, the Harvard School of Public Health, and the Karolinska Institutet in Stockholm has just released the results of a study aimed at settling the controversy as to whether or not ALA is detrimental when it comes to prostate cancer. The researchers also determined the effect of other fatty acids, including fish oils, on prostate cancer risk.

The study involved 47,866 male American health professionals who were followed over a 14-year period beginning in 1986. The participants completed detailed food frequency questionnaires in 1986, 1990 and 1994. By the year 2000, 2965 new cases of prostate cancer had been reported with 448 of these being advanced (metastasized) or fatal. The overall incidence of new prostate cancer detected over the 14- year period was 0.5% per year.

The researchers found no correlation between ALA intake and overall prostate cancer risk, but did observe a strong association between a high ALA intake and the risk of advanced prostate cancer. Men with a high ALA intake (greater than 0.58% of energy or about 1.3 grams/day) were twice as likely to develop advanced prostate cancer as were men with a lower intake (less than 0.37% of energy or about 0.8 grams/day) even after adjusting for all other known variables that could affect the risk. The risk was slightly higher for ALA from non-animal sources than for ALA from meat and dairy sources. There was a trend for red meat, mayonnaise and salad dressings to be associated with a higher risk. The intake of two other abundant fatty acids, linoleic acid and arachidonic acid, was not related to prostate cancer risk.

The team of researchers found a protective effect associated with a high intake of fish oils - eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Men with a daily intake of more than 0.214% of daily energy (about 470 mg/day) were 11% less likely to develop prostate cancer than were men with an intake less than 0.057% of energy (about 125 mg/day). The beneficial effect of EPA plus DHA was particularly pronounced in regard to the incidence of advanced prostate cancer. Fish oil supplements were slightly less effective than fish oils from fatty fish perhaps indicating that vitamin D and vitamin A are necessary to obtain the maximum benefit.
Leitzmann, MF, et al. Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer. American Journal of Clinical Nutrition, Vol. 80, July 2004, pp. 204-16

Selenium and prostate cancer risk

BOSTON, MASSACHUSETTS. At least five major clinical trials have concluded that higher levels of selenium (in blood or toenail clippings) are associated with a sharply reduced risk of prostate cancer. The Nutritional Prevention of Cancer (NPC) trial found that supplementing with 200 micrograms/day of selenium cuts prostate cancer risk in half. Researchers at the Harvard Medical School now weigh in with another study confirming the beneficial effects of selenium. Their study involved 22,000 healthy, male physicians who were enrolled in the study in 1982 and had blood samples taken at that time. Sufficient samples to analyze for selenium content and PSA level were available for 586 men diagnosed with prostate cancer as well as for 577 controls matched for age and smoking status.

After 13 years of follow-up the researchers concluded that study participants with a plasma selenium level of 0.12-0.19 ppm had a 50% lower incidence of advanced prostate cancer than did men with a level of 0.06-0.09 ppm. The correlation was only apparent in men with a PSA level of more than 4 ng/mL and was particularly strong for those with a baseline (1982) PSA level greater than 10 ng/mL. For these men a high selenium level corresponded to a 70% decrease in the risk of advanced prostate cancer. The researchers also observed a trend for a lower incidence of localized prostate cancer with high selenium levels, but this trend was not statistically significant. They conclude that selenium is perhaps not too effective in preventing the initiation of prostate cancer, but that it is highly effective in slowing down tumor progression. They believe that selenium acts by selectively killing off cells whose DNA has been extensively damaged, by inhibiting cellular proliferation, and by its role as a key component of glutathione peroxidase, which protects cells from peroxide damage.
Li, H, et al. A prospective study of plasma selenium levels and prostate cancer risk. Journal of the National Cancer Institute, Vol. 96, May 5, 2004, pp. 696-703
Taylor, PR, et al. Science peels the onion of selenium effects on prostate carcinogenesis. Journal of the National Cancer Institute, Vol. 96, May 5, 2004, pp. 645-47 (editorial)

Editor’s comment: The evidence is now indeed overwhelming that selenium helps protect against prostate cancer. While this study concluded that the protection mainly involves slowing down tumor progression, other studies have shown that selenium also helps prevent initiation of the cancer. Thus daily supplementation with 200 micrograms of selenium should be an integral part of all supplementation programs for men.

Share This