By, Robert A. Wascher, MD, FACS
The information in this column is intended for informational purposes only, and does not constitute medical advice or recommendations by the author. Please consult with your physician before making any lifestyle or medication changes, or if you have any other concerns regarding your health.
DIET & PROSTATE CANCER RISK
The prostate gland is a walnut-sized gland that is attached to the bottom of the bladder. The prostate gland wraps around the male urethra as it arises from the bladder, and several ducts that run between the prostate gland and the urethra allow the pro-static secretions to be expelled into the urethra at the time of ejaculation. These prostatic secretions, which constitute about 20 percent of the volume of semen, help to create the optimal chemical environment for sperm to thrive and migrate within the female genital tract, thereby enhancing sperm function.
In 2009, an estimated 192,000 new cases of prostate cancer will be diagnosed, and approximately 27,000 men will die of this disease in the same year. Prostate cancer is the most common non-skin cancer that occurs in men, and is the second most common cause of cancer death in men. Prostate cancer afflicts 1 out of every 6 American men during their lifetimes, and accounts for 25 percent of all cancer diagnoses in men (similar to the percentage of breast cancer cases among all cancer cases diagnosed in women). As with the great majority of breast cancer cases, most prostate cancers appear to be stimulated to grow and spread by sex hormones produced by the gonads (and, specifically, by testosterone and other androgens produced by the testes, and by other tissues in the body).
There continues to be considerable debate about the impact of diet on prostate cancer risk, as a result of the contradictory conclusions of most epidemiological research studies regarding dietary factors and cancer risk, including prostate cancer (which is, in turn, a reflection of the relatively low scientific power of dietary survey-based studies, in general). Now, a large new prospective European clinical study has raised the possibility that the level of some dietary nutrients (isoflavones) in the blood may actually have an impact on prostate cancer risk. This study’s findings appear in the current volume of the British Journal of Cancer.
The patient volunteers in this particular study were part of a huge and ongoing prospective clinical research study, the European Prospective Investigation into Cancer and Nutrition study (EPIC study). Among the approximately 500,000 participants in the EPIC study, 950 men who were newly diagnosed with prostate cancer during the course of the study and 1,042 men who had no evidence of prostate cancer were evaluated for this particular prostate cancer sub-study.
Isoflavones belong to a group of compounds referred to as phytoestrogens, which are found in certain foods. Phytoestrogens are substances found in certain edible plants, and are known to have weak estrogen-like effects (estrogen is the dominant female sex hormone). Soybeans, and soybean-derived soy proteins, represent the richest source of dietary isoflavones, although some other types of beans, nuts, fruits and vegetables contain low concentrations of isoflavones. Lignans are another group of natural plant-based compounds that are considered to be phytoestrogens. Lignans are found in flax seeds, whole wheat flour, tea, some fruits, and other cereal grains.
In this prostate cancer prevention study, all of the patient volunteers had their blood tested for phytoestrogens at the time that they entered into the study. An especially interesting, and important, aspect of this study is that blood levels of isoflavones and lignans were tested in all of these 1,992 men, and before prostate cancer was diagnosed in the 950 men who were diagnosed with this form of cancer during the course of this study. Additionally, all of the study participants completed the usual dietary and general health surveys that are commonly used in epidemiological studies. Thus, this particular cancer prevention study relied not only on subjective and bias-prone dietary surveys, but also upon objective measurements of isoflavone and lignan concentrations in the blood of all of these men.
While prostate cancer risk did not appear to vary with the concentration of lignans in the blood, the concentration of the isoflavone phytoestrogen genistein in the blood did, in fact, correlate with prostate cancer risk. The results of this study revealed that high serum concentrations of genistein were associated with a 26 percent relative reduction in the risk of developing prostate cancer.
This study builds upon a previous Japanese study, which also measured phytoestrogen levels in the blood, and which reported a decrease in prostate cancer risk with high blood levels of genistein, although this observation, in the Japanese study, did not quite reach the level of statistical significance that is needed to scientifically validate such research findings. (The EPIC Study’s findings regarding genistein and prostate cancer risk did, however, meet this “statistically significant” threshold.)
In summary, therefore, this innovative prospective clinical research study identified an apparent significant reduction in the risk of developing prostate cancer among older men who had high levels of the isoflavone genistein circulating in their blood. As phytoestrogens are absorbed in the GI tract from plants containing high concentrations of these compounds, and as clinical studies based solely upon dietary surveys are notoriously inaccurate, this particular study’s direct measurement of phytoestrogen levels in the blood of its patient volunteers is a critically important innovation, and considerably increases the likelihood that the findings of this study are clinically significantly.
I will have much more to say, dear readers, about diet and prostate cancer prevention, as well as many other clinical evidence-based lifestyle and dietary strategies to reduce your risk of developing all of the top ten cancer killers, in my forthcoming book, “A Cancer Prevention Guide for the Human Race,” which should be available in the spring of 2010.
Disclaimer: As always, my advice to readers is to seek the advice of your physician before making any significant changes in medications, diet, or level of physical activity
Dr. Wascher is an oncologic surgeon, a professor of surgery, a widely published author, and a Surgical Oncologist at the Kaiser Permanente healthcare system in Orange County, California
(Anticipated Publication Date: March 2010)
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Robert A. Wascher, MD, FACS
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9-28-2008: Publication & Citation Bias in Favor of Industry-Funded Research?
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