Zinc – a master element to optimize testosterone in men.
Zinc (Zn) is the most abundant trace metal in the human after iron. It cannot be deposited in the body, the extra Zn is excreted together with sweat, and other discharges. Therefore, regular dietary intake of the mineral is required. The human body contains 2–4 grams of Zn and most of it (nearly 90%) is found in muscles and bones with the highest concentrations in the prostate and semen. Zn is the key element in the male reproduction system determining prostate gland function and growth of reproductive organs. Zinc is a component of over 300 enzymes and 1000 transcription factors and involved in almost all physiological functions of our body: growth, immune response, reproduction, DNA synthesis, expression of genes, and cell division. Here we will focus on how Zn stimulates testosterone production and thereby defines the reproductive health in men.
Clinical research backing up the benefits of zinc supplementation.
Zn deficiency leads to a lowered testis volume, and weight, gonadal dysfunction, poor development of secondary sex characteristics, and infertility in males. Actually, we know that all this happens as a result of low serum testosterone levels, showing that lack of Zn in the body has the same effects as a shortage of testosterone.
Back in 1992, Hunt C.D. and colleagues noticed that low Zinc levels have a negative effect on serum testosterone concentration. Young volunteers, who consumed 10.4 mg Zn/d for 35 days, showed increased semen volume by 32% and serum testosterone concentrations by 19% compared with them, when they were consuming 1.4 mg Zn/d.
Severe and moderate deficiency of zinc is associated with hypogonadism in men, but the marginal deficiency which is often observed in men with age is overlooked. Prasad A S et al. (1997) found that Zn supplementation of marginally zinc-deficient normal elderly men for six months resulted in a doubling of serum testosterone from 8.3 +/- 6.3 to 16.0 +/- 4.4 nmol/L (p = 0.02). So, Zn may play an important role in modulating serum testosterone levels in normal men.
Zn is a marker of prostatic function. Deng C.H. et al. (2005) showed that Zn supplementation may be an efficient strategy for the treatment of infertile males with chronic prostatitis. Zn concentration in the semen and sperm quality were improved markedly in the patients who had received zinc as compared with those who had not.
Thus, zinc stimulates testosterone synthesis on the background of mineral deficiency. However, if you already have a balance of Zn in your body probably, extra Zn supplementation will not have any testosterone boosting effect. On the contrary, too much Zn may cause imbalances to Zn-dependant biological molecules and have negative health consequences.
How does zinc affect testosterone synthesis?
In the testes, large amounts of zinc are concentrated in Leydig cells; it is in these cells that testosterone is synthesized. There is much evidence that Zn depletion results in damage of Leydig cells and hence lowering their density in the testis due to oxidative stress. And as a result, testosterone production in the testes is affected.
5α-reductase is an enzyme necessary for the conversion of testosterone into a more potent form, 5α-dihydrotestosterone, which binds to the androgen receptors more readily than testosterone. As to the effect of Zn on the 5α-reductase, the available research data are ambiguous. The generally accepted point of the inhibitory role of Zn on 5α-reductase activity is grounded just on the results of one in vitro study. Stamatiadis D. et al (1988) showed that when added at concentrations of 3 or 9 mmol/1, Zn was capable to inhibit 5α‐reductase activity in human skin. At high concentrations, zinc could completely inhibit the enzyme activity.
In men, elevated 5AR activity is associated with obesity, age-related overgrowth of prostate, and premature baldness. For the treatment of prostate conditions and hormone-related baldness, inhibitors of 5AR finasteride (Proscar®, Propecia®) and dutasteride (Avodart®) prescribed the most. Supplements containing Saw Palmetto extract are the most popular over-the-counter remedies, with the same 5AR inhibitory effect. But here, one has to understand that over-inhibition of 5α-reductase lowers the DHT synthesis, resulting in elevated levels of testosterone. The consequent aromatization of testosterone to estradiol may cause breast enlargement, impotence, decreased libido, and decreased ejaculate volume- the known side effects of 5AR inhibitor drugs.
So, you might be asking, does Zn really inhibit 5AR in vivo?
Netter, A et al. (1981) reported interesting results from a human study demonstrating an activation effect of zinc therapy on plasma dihydrotestosterone. In this research, 37 patients with infertility of more than five years duration were divided into two groups. In the first group (22 patients, testosterone less than 4.8 ng/ml), Zn supplementation resulted in a significant elevation of testosterone, DHT, and sperm number. Nine wives became pregnant. In the second group (15 patients, testosterone greater than 4.8 ng/ml), Zn administration resulted in no change in the testosterone levels and sperm count, while DHT increased significantly.
While the results of the first group are expectable, the results of the second group show a stimulatory role of zinc in the 5α-reductase activity and contradict the results of in vitro study presented earlier.
Zn deficiency also affects the normal functioning of the hypothalamus-pituitary-gonadal axis, lowers the function of the luteinizing hormone receptor, and lessens steroid synthesis. HPG axis is the principal hormonal network of the body regulating testosterone production. Moreover, Zn reduces the harmful consequences of heat stress, heavy metals, and fluoride.
Zn supports proper thyroid functioning by producing thyroid-releasing hormones in the brain. That can also affect testosterone levels.
Mehmet Kilic and colleagues (2006) studied resting and exhaustion levels of thyroid hormones and total and free testosterone in professional wrestlers before and after Zn supplementation ((3 mg/kg/day) for 4 weeks). The study showed that exhaustion workout significantly diminished both thyroid hormones and testosterone activities, but 4-week zinc supplementation may prevent this inhibition in wrestlers.
Later (2007) Mehmet Kilic got similar results on sedentary males after exhaustion bicycle exercise. The Zn supplementation dosage and its duration were as in the previous study. The results showed that supplementation of a physiologic dose of zinc can be beneficial to performance both in athletes and sedentary individuals. Improvements in free-testosterone levels in both studies may indicate to the inhibition effect of Zn on sex-hormone-binding globulin.
Zinc deficiency has also been associated with increased expression of estrogen receptors. The enzyme aromatase converts testosterone to estrogen and zinc decreases aromatase activity, so preventing the excessive conversion of testosterone to estrogen.
The evidence presented above leaves no doubt that Zn does increase testosterone levels at least in those who are deficient in Zn. Zn supplementation proved to boost testosterone levels both in young and elderly men depleted in Zn, alleviates hormonal imbalances associated with exhausting workouts both in professional athletes and sedentary people, and maybe an efficient strategy to treat infertility of hormonal etiology.
How much zinc can you take?
The Recommended Dietary Allowances (RDAs) for zinc are 8 and 11 mg/day for women and men, respectively. For zinc labeling purposes 100% of the Daily Value is accepted to be 11 mg. The safe upper limit in the United States deemed to be 40 mg, in the European Union – 25 mg. Please note that some companies make zinc tablets well above the recommended daily dosage. For instance, zinc 50 mg tablets of GNC.
If you are involved in daily exhausting exercises, you may need to increase your daily dosing to compensate for the elevated loss of Zn. Since too much zinc depletes copper, do not forget to supplement with copper too. Take them at a 10:1 ratio.
Zinc is a master element in natural testosterone optimization, and every man should be aware of it. If you feel testosterone deficiency signs we talked earlier, start first optimizing your microelements and Zn may prove the key element that will make a difference.
Consult your doctor before you take any supplement.
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- Mehmet Kilic et al. The effect of exhaustion exercise on thyroid hormones and testosterone levels of elite athletes receiving oral zinc. Neuro Endocrinol Lett Feb-Apr 2006; 27(1-2):247-52.
- Mehmet Kilic. Effect of fatiguing bicycle exercise on thyroid hormone and testosterone levels in sedentary males supplemented with oral zinc. Neuro Endocrinol Lett. 2007 Oct;28(5):681-5.
- Prasad A S et al. Zinc status and serum testosterone levels of healthy adults. Nutrition. 1996 May;12(5):344-8.
- Stamatiadis D, Bulteau-Portois MC, Mowszowicz I (November 1988). “Inhibition of 5 alpha-reductase activity in human skin by zinc and azelaic acid”. The British Journal of Dermatology. 119 (5): 627–32.
- Netter, A et al. Effect of zinc administration on plasma testosterone, dihydrotestosterone, and sperm count. Arch Androl. 1981 Aug;7(1):69-73.