The prostate gland is a chestnut-sized organ at the base of the urinary bladder in men. The urethra, which is the tube that empties urine from the bladder, runs through the middle of the prostate. As a man ages, his prostate enlarges, often constricting the urethra and interfering with urination. The prostate is also a common site for cancer. In fact, according to the American Cancer Society, prostate cancer is the second most common malignancy in American men. Zinc plays an integral a role in prostate health, but optimal levels of zinc intake have not yet been clearly defined.
Healthy Prostate
Zinc probably participates in more enzyme-mediated metabolic processes than any other mineral, and the cells in a healthy prostate accumulate more zinc than any other soft tissue in the body. According to a 1998 article in Prostate, the high zinc concentrations in prostate cells inhibit the activity of an enzyme that normally funnels citrate into intracellular energy production. Healthy prostate cells secrete the unused citrate into the seminal fluid, where it is used by energy-hungry sperm.
Prostate Enlargement
The reasons for prostate enlargement in older men are a matter of some debate, but most researchers agree that hormones play a role. The process involves a series of physiologic changes that culminate in a condition called benign prostatic hyperplasia, or BPH. Blood levels of testosterone, a male hormone, normally fall as men age. One of testosterone's roles is to promote the absorption of zinc by prostate cells, so as testosterone levels fall, so do prostatic zinc levels. Paradoxically, as prostatic zinc concentrations decline, 5-alpha reductase, an enzyme that converts testosterone to dihydrotestosterone, or DHT, becomes more active. DHT stimulates prostate cells to grow and divide, so even as testosterone levels fall in older men, the gradually increasing levels of DHT within the prostate cause the organ to enlarge. Other hormones, such as prolactin, may also play a role. BPH is not necessarily associated with prostate cancer.
Prostate Cancer
When prostate cells become cancerous, they lose their ability to concentrate zinc, and they stop secreting citrate. Since the citrate is no longer secreted into the semen, it becomes an energy source for the growth of the tumor. Some researchers believe that this characteristic could serve as a "biomarker" for early malignancy. By measuring citrate levels in semen samples, doctors could possibly detect prostate cancers -- and gauge their aggressiveness -- much earlier. This would add valuable information to the methods physicians use to screen for prostate cancer.
Dosage Uncertain
According to a 1996 Nutrition article, zinc deficiency is prevalent throughout the world, including the United States. Investigators in this study demonstrated that supplementation with zinc in marginally deficient older men was associated with an increase in testosterone production. Conversely, dietary zinc restriction in younger men resulted in a decrease in serum testosterone levels. It appears that dietary zinc plays an important role in modulating testosterone levels, which subsequently regulate prostatic zinc absorption. Zinc absorption in turn influences prostate health. However, the optimal daily dosage of zinc has not been determined. A 2003 study published in the Journal of the National Cancer Institute says that the risk for advanced prostate cancer increases with zinc doses over 100mg daily or with taking zinc supplements for more than 10 years. The research team questioned whether contaminants -- especially cadmium -- in commercially available zinc supplements could have contributed to this observation.
Discussion
It is difficult to decide what dose of zinc is safe, particularly when nutritionists and other scientists cannot agree on optimal doses. On the one hand, zinc appears to play a vital role in prostate health, and given the widespread prevalence of zinc deficiency, it might seem prudent to take supplemental doses. On the other hand, excessive doses might increase your risk for prostate cancer. According to the Mayo Clinic, the recommended dietary allowance for adult males is 15mg of zinc daily. Zinc gluconate may contain lower levels of cadmium than supplements containing zinc sulfate or amino acid chelates.
References
- American Cancer Society: Prostate Cancer
- Prostate: Novel Role of Zinc in the Regulation of Prostate Citrate Metabolism and Its Implications in Prostate Cancer
- Canadian Urological Association Journal: The Role of 5-alpha Reductase Inhibitors in Prostate Pathophysiology: Is There an Additional Advantage to Inhibition of Type 1 Isoenzyme?
- Prostate Cancer and Prostatic Diseases: Prostatic Fluid Electrolyte Composition for the Screening of Prostate Cancer: A Potential Solution to a Major Problem
- Nutrition: Zinc Status and Serum Testosterone Levels of Healthy Adults
- Journal of the National Cancer Institute: Zinc Supplement Use and Risk of Prostate Cancer
