Prostate Cancer Prevention
by Hans R. Larsen, MSc ChE and William R. Ware, PhD
FINASTERIDE (PROSCAR) AND PREVENTION OF PROSTATE CANCER
The American Society of Clinical Oncology and the American Urological Association (ASCO and AUA) have issued a new guideline on the use of 5-alpha reductase inhibitors (5-ARI) for cancer chemoprevention. They found 15 randomized clinical trials that met their inclusion criteria. The main conclusion was that 5-ARI therapy during a 7-year period reduces the relative risk of developing prostate cancer by 25%. The absolute risk reduction however was only 1.4% which leads to about 71 persons needed to treat to prevent one cancer. Another way of looking at this result is that if 1000 men were followed over a period of 7 years, 59 would be expected to develop prostate cancer, and if they all took the 5-ARI, 45 would still develop cancer. This risk reduction is consistent with the result from the Prostate Cancer Prevention Trial which started in 1993 and was stopped in 2004 because of this same risk reduction. However, enthusiasm that should have arisen from this trial result, based on the 25% figure, was dramatically dampened by the suggestion that finasteride increased the risk of high-grade cancer. A majority (8 of 10) of members of the ASCO-AUA panel judged this higher observed incidence of high-grade cancer in the finasteride group to be due to confounding and thus not real. Finasteride is prescribed to relieve the symptoms of benign prostate hyperplasia (BPH - enlarged prostate) and 11 to 40 men experience side effects for every 1000 taking the drug. These include decreased sex drive and erectile dysfunction. The position taken by the ASCO-AUA is that men who are asymptomatic with a PSA equal to or less than 3.0 ng/mL may benefit from a discussion of the benefits of 5-ARIs vs. the risk of side effects. For men taking the drug for symptoms associated with BPH, the guidelines suggest that a discussion is in order to acquaint them with the possibility of increased risk of high-grade cancer, but as pointed out, the panel considered this risk unlikely, and thus given the need for the drug in the context of BPH, the potential cancer prevention is an added bonus. An additional problem with 5-ARI therapy is an approximate 50% drop in PSA which must then adjusted when applying cut-offs for triggering a biopsy. The panel did not take a position or a revised cut-off.
While obtaining a 25% risk reduction seems very appealing merely by popping a pill daily, individuals who would otherwise not take 5-ARIs need to seriously consider the very high number needed to treat to prevent one cancer. It is not hard to find physicians who regard 71 as too high to justify an intervention that is not totally risk free. There is also cost to consider. Finasteride can cost up to $60 U.S. per month.
GAMMA-E HELPS PREVENT PROSTATE CANCER
The potential anti-cancer properties of gamma-tocopherol appear to be under appreciated, given that most people appear to think of vitamin E only in terms of the common supplement, the alpha form. In a recent review titled Gamma-Tocopherol--An Underestimated Vitamin?, Wagner et al discuss a number of studies that relate to this question. One found a 5-fold reduction in prostate cancer risk for the highest vs. lowest quintiles of gamma-tocopherol intake. Another serum level study also found the same 5-fold reduction. However, a large trial involving U.S. physicians that also looked at serum levels failed to find a similar association. In addition, Wagner et al point out that gamma-tocopherol is more effective than alpha-tocopherol in inhibiting prostate cancer cells, reducing oxidative DNA damage and scavenging certain mutagens. Obviously, more studies are needed, but the evidence of the benefits of gamma-tocopherol in regard to prostate cancer is accumulating. In fact, it may occur to some readers that the SELECT trial may not be using the ideal form of vitamin E and that a negative outcome of this trial when it finally reports might well kill interest in vitamin E in general, including the gamma form.
Gamma-tocopherol is also available in supplements, generally as mixed tocopherols. Careful label reading is required since IU may be quoted (conversion 0.15 IU per mg) but it is common for only a total in IUs or milligrams for the beta, gamma and delta combined to be displayed. Products are available that contain 200 or more mg per capsule of the gamma form. Given that many individuals do not eat foods rich in the gamma form of vitamin E, supplements containing this form appear to be of interest.
TOMATO PRODUCTS AND ADVANCED PROSTATE CANCER
The follow-up trial was part of the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO). Participants were selected who underwent annual standardized screening for prostate cancer (PSA at entry and annually for 5 years and a digital rectal exam at entry and annually for 3 years). Thus this was a PSA-era study. No association was found between serum lycopene and total prostate cancer diagnosis risk or aggressive prostate cancer risk. The authors conclude that, consistent with other recent publications, these results suggest that lycopene or tomato- based regimens will not be effective in prostate cancer prevention.
The FDA report was based on a review of the literature and found "no credible evidence to support the association between lycopene intake and a reduced risk of prostate cancer." However, they mention finding very limited evidence to support the association between tomato consumption and reduced risks of prostate cancer.
This latter report prompted Edward Giovannucci, a very well known epidemiologist from Harvard, to write an editorial trying to reconcile the FDA position with earlier studies that did indeed show benefit. His thesis is that the newer studies fail to find benefit from lycopene or tomato products because the studies are all done in the PSA era. Before the widespread use of PSA testing for screening purposes, most cancers that were diagnosed had progressed to a relatively advanced stage. What was being detected were manifestations of advanced disease such as metastasis and tumor growth outside the prostate itself. In the PSA era, most of the cancers detected would never have attracted clinical attention and include small, low-grade and indolent tumors. Thus studies of tomatoes and lycopene in the PSA era with the endpoint of cancer diagnosis are looking at the question of benefits during the early stages of disease development, whereas in earlier times, the potential benefit extended over a much longer period in the natural history of the disease. Consistent with this, Giovannucci points out that in the Health Professional's Follow-Up study (HPFS), the initial analysis of the data for the period 1986 to 1992 found an inverse association between tomato sauce intake and total prostate cancer incidence and the association was stronger for advanced cancer. Later analysis for the period 1992-1998 which was during the PSA era, the association was attenuated and weak but a strong association persisted for metastatic cancer. Combined data for these two periods gave a 66% risk reduction for = 2 servings per week to <1 serving per month. Finally an analysis of the data found no association between tomato sauce and the risk of diagnosis of organ-confined disease. Thus in the PSA era, the benefits of tomato sauce with regard to advanced cancer were swamped by the huge numbers of early non-advanced cases. In the HPFS study, Giovannucci comments that only strict criteria for aggressive behavior such as invasion into the seminal vesicle or metastasis were adequate to detect the association between tomato paste and an increased risk of fatal prostate cancer. He also points out that the FDA review was not designed to take into account these issues and the data needed are sparse.
These same observations apply to the PLCO study which was done in the PSA era. Thus it appears that tomatoes and lycopene provide benefit only in terms of influencing advanced cancer or offering benefit that is only significant when the exposure is over the full initiation and progression of the disease, as was the case in the early studies. It would appear that abandoning cooked tomato products like tomato sauce, and as well even supplemental lycopene, on the basis or recent studies is somewhat premature. Furthermore, it may be unrealistic to assume that studies will be carried out that might resolve the issues discussed, given the widespread PSA screening at present is the norm.
OMEGA-3 FATTY ACIDS AND PROSTATE CANCER PREVENTION
VITAMIN D AND PROSTATE CANCER
These results are surprising because of several recent studies that connect sun exposure to a reduced risk of prostate cancer. In one 528 prostate cancer patients and 442 basal cell carcinoma cases (a UV induced cancer) were examined for a correlation between cancer and sun exposure. Both groups were measured the same way as regards sun exposure. For those with the highest sun exposure, the risk of basal cell carcinoma was the highest, and for those with prostate cancer it was the lowest. In another study, increased sun exposure decreased prostate cancer mortality. In a study that looked at geographical distributions of UV intensity and prostate cancer mortality in the US, the expected variation with latitude was observed, i.e. those living in the higher latitudes had higher risk. Why this is not reflected in the Physicians Health Study as a more dramatic correlation between serum 25(OH)D and prostate cancer is not clear.
DISCOURAGING NEWS FROM SELECT TRIAL
When the trial design was announced, there was discussion in the literature regarding the form of vitamin E used since natural vitamin E is much more effective in general and the form in food is in fact gamma tocopherol. It is doubtful that the trial will be repeated with either the natural form or the gamma form and thus we will never know if the null result was due to the use of the synthetic form of vitamin E. Nevertheless, the form of selenium used is generally considered to be satisfactory from the point of view of bioavailability (L-selenomethionine), and it alone was not effective in this trial. But, it has been pointed out that statin drugs interfere with the synthesis of selenoproteins, glutathione peroxidase and in particular selenoprotein N. But the SELECT trial has not indicated results from stratification to see if selenium alone was effective in statin non- users. In the age group studied, there were no doubt a large number of statin users who may have had the beneficial effects of selenium blocked by the statin enzyme inhibition. In fact, it has been postulated that the inhibition of selenoproteins may be related to the side effects of statins such as rhabdomyolysis and polyneuropathy. Thus this study was far from ideal to answer the target question and in fact may have been fatally flawed.
Eating fish may help prevent prostate cancer
Design of the SELECT trial
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.
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.
Fish oils help prevent prostate cancer
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.
Selenium and prostate cancer risk
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.
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.
Testosterone and Alzheimer's disease
Editor's comment: Testosterone supplementation should be approached with great caution and only done with the cooperation of a physician as it may increase the risk of prostate cancer.
Cancer trends in the USA
Cancer of the colon and rectum
The report concludes that overall cancer incidence and death rates began to stabilize in the mid to late
1990s, but have lately shown signs of increasing again.
Selenium absorption by prostate tissue
If selenium proves to be cancer preventive it is clearly important to know whether selenium levels as measured in a blood sample correlates with actual selenium levels in prostate tissue. Researchers at the University of Queensland recently set out to answer this question. Their clinical trial involved 51 men who had been scheduled for transurethral resection for prostate enlargement. The men were randomly assigned to serve as controls or to receive selenium yeast tablets daily for one month prior to surgery. The tablets provided a total of 200 micrograms/day of selenium. Blood samples were taken at the beginning of the 30-day trial and on the day of surgery and the selenium content of red blood cells was compared to the selenium content of prostate tissue removed during surgery.
The researchers found that the red blood cell level of selenium had increased from 173 ng/mL to 209
ng/mL in the supplemented group with no significant change among controls. The selenium level in
prostate tissue from supplemented men was significantly higher than among controls (241 ng/g versus
196 ng/g). The researchers conclude that selenium supplementation is effective in raising selenium
levels in both prostate tissue and red blood cells, but conclude that selenium values from blood testing do
not correlate with values obtained from testing of prostate tissue.
Prostate cancer: Risk factors and prevention
Several studies have found a clear association between the western lifestyle and an increased risk of prostate cancer. A high intake of fat, meat and dairy products has been found to be particularly detrimental. Consuming fried or charcoal-grilled red meat has been clearly associated with increased risk. A high intake of alpha-linolenic acid and calcium from dairy products has both been associated with higher risk. A Swedish study found that men who consumed 600 mg/day of calcium from dairy products had a 32% greater risk than those consuming 150 mg/day or less.
Smoking, degree of physical activity, and alcohol consumption have not been associated with an increased risk and neither has vasectomy.
Soybean products (soy milk or tofu) have been found to have a preventive effect as has a high intake of
tomato products, lycopene, selenium, and vitamin E. Supplementation with selenium reduced risk by
66% in one study while vitamin E supplementation lowered it by 40%. A large study involving 32,400 men
is currently underway to confirm the benefits of vitamin-E and selenium supplementation. Results are
expected by 2013.
Prostate cancer and antioxidants
LOS ANGELES, CALIFORNIA. A team of University of California (San Diego) researchers recently reported that PC-SPES, a much touted herbal remedy for prostate cancer, had been found to be heavily contaminated and had been taken off the market. Nevertheless, researchers at the UCLA Center for Human Nutrition in Los Angeles now report that they have found PC-SPES to be highly effective in preventing the initiation and progression of colon cancer. They evaluated PC-SPES in vitro using three different colon cancer cell lines. They found that the herbal compound caused a 95 per cent inhibition of cell proliferation in all three lines. In contrast, estradiol did not stop cell proliferation at all. Thus it is unlikely that the observed effect of PC-SPES is due to possible contamination with diethylstilbestrol, another estrogenic compound. The researchers also evaluated PC-SPES (250 mg/kg/day) in laboratory mice genetically engineered to develop multiple tumours in the gastrointestinal tract within a few weeks after birth. They found that mice treated 5 times a week for 10 weeks with PC-SPES developed 58 per cent less tumours than did control mice. They conclude that the components of PC-SPES, either independently or in combination, act to produce a drastic reduction in tumour initiation and progression in the gastrointestinal tract.
Huerta, Sergio, et al. PC-SPES inhibits colon cancer growth in vitro and in vivo. Cancer Research, Vol. 62, September 15, 2002, pp. 5204-09
Tomato sauce and prostate cancer
Selenium prevents prostate cancer
The researchers believe that much of the beneficial effect of selenium is due to its vital role in maintaining
adequate levels of the body's main antioxidant, glutathione peroxidase. They conclude that selenium
supplementation may reduce the risk of prostate cancer and that supplementation may be particularly
important for older men. NOTE: The recommended daily intake of selenium is 55 micrograms with an
upper safe limit of 400 micrograms/day. However, most supplementation studies have used 200
Prostate cancer and lycopene
The researchers conclude that lycopene supplementation lowers PSA levels; they observed an average
18 per cent decrease in the lycopene group as compared to a 14 per cent increase in the control group.
The level of the tumor suppressing protein Cx43 in the malignant part of the tumor was found to be
substantially higher in the lycopene group. It was also apparent that tumors tended to be smaller and
more sharply defined (less encroachment into surrounding healthy tissue) in the lycopene group. No
adverse effects of the lycopene supplementation were reported by the patients or their physicians. The
researchers conclude that lycopene is likely to be beneficial for both prevention and treatment of prostate
cancer, but urge larger trials to confirm this.
Sun exposure prevents prostate cancer
A history of regular foreign holidays, presumably in sunnier climes, also had a protective effect with men
having had such holidays having a 60 per cent lower risk of prostate cancer. Regular sun bathing was
also found to be protective. The risk of prostate cancer was not associated with skin type, hair colour or
eye colour, and the associations with sun exposure were not affected by including occupation, vasectomy
or dietary factors in the analysis.
Editor's Note: Excessive sun exposure has
been linked to an increased risk of certain non-melanoma skin cancers. These cancers, however, are
rarely fatal whereas prostate cancer often is. So on balance, cultivating a healthy suntan is still a good
Fish consumption helps prevent prostate cancer
he Swedish study involved 3136 pairs of male twins born between 1886 and 1925. The participants
completed food frequency questionnaires in 1961 and 1967 and were then followed up for 30 years. By
December 31, 1997 the researchers had recorded 466 diagnoses of prostate cancer (340 fatal ones).
The average age of diagnosis was 76.7 years. After adjusting for other known risk factors the
researchers conclude that men who never eat fish have a two- to three-fold higher risk of prostate cancer
than do men who eat moderate to high amounts. The researchers emphasize that only fatty fish such as
salmon, herring and mackerel, which contain high amounts of omega-3 fatty acids (EPA and DHA), would
be expected to be beneficial.
Lycopene and cancer
Eat your broccoli and avoid prostate cancer
The intake of fruit did not significantly affect prostate cancer risk.
However, men who consumed 28 or more servings of vegetables per week were
found to have a 35 per cent lower risk than men who consumed fewer than 14
servings per week. When limiting the analysis to cruciferous vegetables only
the protective effect was found to be even more pronounced. Men who ate three
or more servings of cruciferous vegetables (broccoli, cauliflower, brussel
sprouts, cabbage) per week had a 41 per cent lower risk of developing prostate
cancer than did men who ate less than one serving a week. A high intake of
lutein plus zeaxanthin (2000 micrograms/day or more) was associated with a 32
per cent decrease in risk, but this association was not statistically
significant. The researchers found no correlation between the intake of
tomato products or lycopene and prostate cancer risk.
Beta-carotene and cancer
Researchers at the Harvard Medical School have just released the results of a major study aimed at
evaluating the effects of beta-carotene supplementation among women. The study involved almost
40,000 healthy female health professionals (aged 45 years or older). The women were randomized into
two groups with one group receiving 50 mg of synthetic beta-carotene on alternate days and the other
group receiving a placebo. The 2.1-year supplementation phase of the study was followed by a two-year
observation period. At the end of the four years 747 cases of cancer and 218 cases of cardiovascular
incidents (heart attack, stroke, and death) had occurred among the women. There were no significant
differences in the incidence of cancer, cardiovascular events or death from all causes in the two groups.
This also held true when just the smokers among the women were considered.
Fish oils help prevent prostate cancer
Evaluation of the collected data showed a clear correlation between blood level of EPA and DHA and the presence of prostate cancer. Study participants with levels in the highest quartile were found to have a 40 per cent lower incidence than participants with levels in the lowest quartile. This relationship held true even when adjusted for age, height, use of NSAIDs (non- steroidal anti-inflammatory drugs), socio-economic status, and estimated intake of lycopene and polyunsaturated fats.
The researchers also found that men with low socio-economic status, a low
intake of lycopene, and non-regular use of NSAIDs were more likely to develop
prostate cancer. They did not, however, find any correlation between self-
reported intake of EPA and DHA indicating that food frequency questionnaires
are not an accurate method for estimating fish oil intake. The researchers
speculate that fish oils may prevent the progression of prostate cancer by
inhibiting the biosynthesis of eicosanoids from arachidonic acid.
Diet is vital in cancer prevention
Tomato sauce protects against prostate cancer
Physical activity protects against prostate cancer
Vitamin A may prevent prostate cancer
Pasquali, Daniela, et al. Abnormal level of retinoic acid in prostate cancer tissues. Journal of Clinical Endocrinology and Metabolism, Vol. 81, No. 6, June 1996, pp. 2186-91
Selenium protects against cancer
Beans and garden peas may reduce risk for prostate cancer
Among foods and other nutrients examined, significant associations were
observed for garlic (food only or food plus supplements), baked beans, vitamin
B6 and garden peas. The association with garlic and vitamin B6 was later found
to be statistically insignificant when adjusted for social class. Another
recent study in England found that men who ate beans and peas more than once a
week had a 37 per cent reduction in risk compared to men who ate these foods
less often. The confirmed risks for prostate cancer include age, a family
history of prostate cancer, social class and ethnic group/country of
residence. A history of prostate cancer in fathers and brothers was
associated with a two- to three-fold increased risk for the disease and manual
workers were found to have a 63 per cent higher risk of prostate cancer than
did non-manual workers. No correlation was found between risk and alcohol
intake or smoking. Contrary to other recent studies, the researchers found no
effect of increased lycopene intake. However, they point out that their
estimate of lycopene intake was very crude and did not account for the wide
differences in bioavailability of lycopene from different sources. The
researchers also noted that the use of vitamin E supplements was considerably
higher among controls, but no significant correlation with cancer rate was
observed. The researchers conclude that there is, as yet, no clear
correlation between diet and prostate cancer risk but that the effect of a
high intake of vitamin B6 (pyridoxine), garlic, peas and beans warrants
Finasteride does not prevent prostate cancer
Selenium intake and prostate cancer
Lycopene and prostate cancer
DHEA protects against prostate cancer
CHICAGO, ILLINOIS Prostate cancer is the second most common cause of cancer
death in Western male populations. It is estimated that about 18 per cent of
American men will develop prostate cancer during their lifetime. Some
researchers believe that many more have the beginnings of prostate cancer, but
die from other causes before the cancer becomes invasive and fatal. Research
has shown that the hormone DHEA (dehydroepiandrosterone) inhibits the growth
of both human and rat prostate cancer cells in vitro (in test tubes).
Now a team of researchers from the National Cancer Institute, the New York
University School of Medicine, and the ITT Research Institute reports that
DHEA confers significant protection against prostate cancer progression when
given to laboratory rats as part of their diet. Their experiment involved
rats which were given carcinogenic chemicals to induce precancerous lesions in
the prostate. One group of rats had 1000 or 2000 mg of DHEA added to each
kilogram of feed starting one week before inducing the cancer. Other groups
had 2000 mg of DHEA added per kilogram of diet one week before induction, 20
weeks after induction or 40 weeks after induction. The rats received the DHEA
until the experiment was concluded 13 months after cancer induction. Control
rats received no DHEA. The researchers found a very significant decrease in
the progression to full prostate cancer among the rats given DHEA in their
diets. This effect was evident whether the DHEA was given one week before or
20 or 40 weeks after cancer induction. They conclude that DHEA or a suitable
derivative may be effective in preventing the development and progression of
prostate cancer in humans, but caution that more work is required to ensure
the DHEA's hormonal effects (conversion to testosterone and estrogenic
activity) are not detrimental.
Testosterone supplementation and prostate cancer
Now Dr. Richmond Prehn, MD of the University of Washington challenges the
assumption that high androgen levels are a risk factor for prostate cancer.
Dr. Prehn points out that androgen levels decline with age whereas prostate
cancer incidence rises sharply. He suggests that declining androgen levels
may not only lead to benign prostate hyperplasia (BPH), but may also be the
initiator of uncontrolled cell growth which may ultimately lead to cancer. He
further suggests that "androgen supplementation beginning early in the middle
years might, among other possible benefits, largely prevent prostate cancer."
Dr. Prehn cautions that androgen supplementation may be contra-indicated in
older men who already have the seeds of prostate cancer. He also suggests
that an alternating regimen of androgen deprivation and androgen
supplementation should be evaluated as a therapy for prostate cancer.