There is increasing evidence that nutrition may play a significant role in the prevention and/or progression of prostate cancer. There are data to suggest that diet may be a more significant factor in the behavior of the prostate cancer than in either breast or colon cancer.
Autopsy studies have demonstrated that there's evidence of microscopic prostate cancer in approximately 80% of men over 80 years old. This is the same throughout the world and is unrelated to race. However, the incidence of clinically significant prostate cancer is significantly greater in Western countries as opposed to Asian countries. In a study published in the British Journal of Cancer in 1991 by Dr. Shimizu and associates, it was noted that within one generation, there was a four fold to nine fold increase of prostate cancer among Japanese men who had immigrated to the United States in contrast to their counterparts who remained in Japan. In a similar study published in Acta Oncologica in 1991, Dr. Muir and associates found a 3-7 fold increase in the incidence of prostate cancer in Chinese men who had immigrated to the San Francisco bay area. This suggests the presence of either an environmental or nutritional factor that may play a role in stimulating the growth of microscopic cancer to clinically significant cancer.
Of all of these potential factors, the most significant has been the relationship between dietary fat and prostate cancer. Of 14 well performed studies involving more than 3,000 patients with prostate cancer and more than 4,600 patients without prostate cancer, 11 of the 14 studies have shown a positive association between increased dietary fat and higher risk of prostate cancer, with some studies showing a greater than 3 fold increase in cancer incidence. In another group of 5 studies involving close to 100,000 men, there was also positive association between dietary fat and the development of prostate cancer. In a study published in the Journal of the National Cancer Institute in 1993 by Dr. Giovannucci and associates, there was a marked increase in the likelihood of prostate cancer in men with a high dietary fat intake from red meat. These investigators found a strong relationship with the intake of linolenic acid, a fatty acid primarily associated with red meats, with prostate cancer. Similarly, a study from Dr. Rose and associates published in the Journal Cancer in 1986, demonstrated a high correlation between average per capita fat consumption and prostate cancer mortality in a number of countries world wide.
Experimentally, animal studies have demonstrated that the growth of prostate cancer can be markedly inhibited in mice on a low fat or fat free diets. Other studies have also shown a similar effect on prostate cancer in mice fed a diet rich in omega-3 fatty acids. When investigators looked specifically at prostate cancer types that most resemble the ones found in humans, they found that the growth of these tumors was markedly inhibited if a dietary fat content in animals was no greater than 21% of total calories. Furthermore, PSA levels were significantly lower in the animals receiving 21% or fewer of their total calories from fat. These studies were published by Dr. Wang and associates in the Journal of the National Cancer Institute in 1995.
While these studies suggest that a low fat diet may be protective against prostate cancer, it is not known if reducing dietary fat in individuals used to a high fat diet will ultimately reduce their risk of prostate cancer.
OTHER SUBSTANCES THAT MAY INHIBIT PROSTATE CANCER GROWTH
Based on the marked difference between Western and Asian men with regard to the incidence of clinically significant prostate cancer, various studies have been done comparing nutrition in the two populations. In a study published in the British journal Lancet in 1993 by Dr. Aldercreutz and Associates, the concentration of isoflavonoid extracts of soybean were found in concentrations much higher in both the the urine and blood of Japanese men consuming a traditional Japanese diet when compared with that in Finish men on a Western diet. The study suggested that isoflavonoids may play a role in the different incidence rates between Finland and Japan.
Experimentally, in a study by Dr. Wang and Associates published in the Journal of Urology in 1995, the two major constituents of soy protein, genistein and daidzein, were added to established prostate cancer cells growing in test tubes in a laboratory. These soy protein constituents caused significant growth inhibition of the prostate cancer cells. In addition, Genistein at levels consistent with those found in the blood of vegetarian men caused profound drops in the level of PSA in these prostate cancer cells. When these soy extracts were given to rats prior to being injected with prostate cancer cells, there was a 3-fold higher difference in tumor growth and PSA levels in rats who were fed genistein as opposed to those which were not. These studies suggest that a diet rich in soy products, such as the traditional Japanese diet, may be protective against prostate cancer
VITAMINS
In studies looking at the effect of vitamins A, C, D, and E on prostate cancer, it has been found that vitamins D and E may have a protective effect against prostate cancer. In a study published in the New England Journal of Medicine in 1994 by the Alpha-Tocopherol, Beta Carotene cancer prevention study group, the incidence of prostate cancer was 34% lower in men receiving vitamin E supplements. Several studies have also demonstrated that men with higher exposure to sunlight and subsequent higher levels of vitamin D derivatives, had a lower rate of prostate cancer than men with lower levels of vitamin D metabolite 1,25 dihydroxy cholecalciferol. Dr. Schwartz and associates demonstrated that addition of vitamin D derivatives to prostate cancer cells inhibited their growth.
SELENIUM
The essential trace element selenium has been noted to be lower in soils from geographic areas with a higher cancer rate, and the reverse in areas with a low cancer rate. In a large study by the National Prevention of Cancer Study Group published in JAMA in 1996, there was found a 63% decrease in the incidence of prostate cancer and 37% decrease in the overall cancer incidence in men receiving supplemental selenium. This represents the most compelling argument to date that regular ingestion of exogenous selenium may be beneficial as a preventative agent against the development of prostate cancer
In summary, population studies and laboratory evidence increasingly demonstrate that nutritional factors, especially reduced fat intake, soy proteins, vitamin D and E derivatives, and selenium may have a protective effect against prostate cancer.