Scientists have for decades known that a zinc deficiency is associated with decreased testosterone production and other medical conditions. However, lately zinc has been considered a big disappointment by researchers. Studies have shown, for example, that it does not generally increase testosterone significantly or protect from colds as originally thought.
But does that mean you should give up on this mineral altogether? No way! Some guys, like Casanova, have reported near miraculous powers from supplemental zinc. Could there by something to it? Below are five reasons that zinc may in some cases dramatically boost testosterone and substantially improve your sex life:
NOTE: ZMA is a special formulation of zinc and magnesium. The Magnesium is a nice side benefit of ZMA and will likely help you sleep better and avoid Metabolic Syndrome and heart disease. An alternative way of getting your zinc is through oysters, although I certainly wouldn't recommend doing that every day. But we had one poster write in the following:
"On the subject of shellfish, here's another anomaly: one night recently I ate a large plate of raw oysters for dinner, and later experienced very firm nocturnal erections and very sexual dreams (practically to the point of nocturnal emission). This, when it's very rare for me to have a nocturnal erection at all, and never a firm one. I never put much stock in oysters' reputation as an aphrodisiac, but I am now convinced there is something to it."  Casanova himself ate several dozen oysters every day for its supposed aphrodisiacal super powers and oysters do have a lot of zinc.
1. Testosterone. Some research has shown that zinc can increase testosterone. It all started when an absorbable form of Zinc called ZMA (which also contains Magnesium), was created by Victor Conte of Barry Bonds fame. Mr. Conte backed a study that shows a nice increase (34%) in testotserone in young athletes taking ZMA. 
Sounds good, eh? Unfortunately, subsequent research has cast doubt on Mr. Conte's work and showed no testosterone increase with ZMA.  One theory is that supplemention does not boost testosterone except perhaps in individuals who are zinc-depleted. Furthermore, it is tough to determine who is really depleted in zinc and who is not. Some experts recommed, for example, the zinc taste test to determine this. Regardless, it seems that normal, healthy individuals receive little to no benefit as far as testosterone.
However, there is also another interesting explanation. One study on infertile men showed that zinc increased testosterone only in men who were lower in testosterone (less than 480 ng/dl).  Therefore, if you have low testosterone, it may be worth it to try some zinc and see if you can get a little boost. To test your DHT, check out these links: Reasonable Testosterone Labs and The Cheapest Lab Tests for men for some ideas. I have not used most of the labs, so do your own due diligence and am just passing along information that I have picked up on the Peak Testosteorne Forum.
NOTE: Zinc may also boost DHT in some men, which could be good or bad depending on your situation. See my link on Zinc and DHT for more information.
So who might be zinc depleted? One misconception is that, if you happen to be having a lot of sex - you lucky dog! - that you may be making yourself zinc depeleted. However, one study shows that only about 0.3 to 0.45 mg of Zinc, or 2-3% of your body's RDA, is lost during ejaculation.  I also frequently get emails from heavy porn users who have lost their sexual desire and/or erectile strength. (I am talking about guys clearly addicted and spending hours per day and ejaculating 3+ times in a 24 hour period.) There are probably a variety of reasons for their sexual dysfunctions, but low grade zinc depletion does not appear to be one of them. (There is also now evidence that are "numbing" their dopamine receptors as well.)
Heavy exercise and infection also can depelete zinc and often those on a largely vegetarian diet consume less zinc as well. So some of you guys could actually be running low on zinc and benefit from supplementation.
2. Brain Activities: Sleep and Learning. A combination of zinc, magnesium - yes, this is starting to sound a lot like ZMA - and melatonin has been found in one study to be a potent insomnia cure. (See this link on Sleep Aids for more information.) A couple of our posters on The Peak Testosterone Forum have commented how much taking ZMA helps their sleep and, of course, ZMA is one third zinc. This poster recommended taking it about 40 minutes before bed:
"ZMA ..oh yes I like...not only the zinc as Peak mentioned to help keep T at a max (and help with everything in your body!!) but the magnesium is fantastic for helping to induce sleep. I only have one cap a day usually 40 mins before bed and it definitely makes you sleepy. One cap only equates to 10mg of zinc (about 100% RDA) and 150mg of mag which is only 40% RDA."
So there is evidence that zinc plays a role in sleep quality and/or duration. Zinc affects the brain in other ways as well. For example, one study review pointed out the importance of zinc to learning, memory and neuron maintenance / regeneration: "The highest levels of zinc are found in the hippocampus in synaptic vesicles, boutons, and mossy fibers...Zinc plays an important role in axonal and synaptic transmission and is necessary for nucleic acid metabolism and brain tubulin growth and phosphorylation. Lack of zinc has been implicated in impaired DNA, RNA, and protein synthesis during brain development...Furthermore, in children insufficient levels of zinc have been associated with lowered learning ability, apathy, lethargy, and mental retardation."  I'll just point out that the hippocampus is the center of memory and is involved in some higher order thinking processes as well.
3. Estrogen. Zinc actually inhibits the aromatase enzyme, especially in zinc-depleted individuals, and therefore could decrease estrogen.  (It may also inhibit the conversion of testosterone to DHT, which could help your prostate and hair!) At worst it is another tool in our arsenal to optimize and maintain our estrogen at reasonable levels. And, of course, this may be another reason that zinc is a testosterone booster for some men but not others.
4. Dopamine. Researchers have found that zinc is one of the most important minerals regulating dopamine.  It turns out that zinc is present in your neuron's synapses and plays several major roles in neurotransmission. Zinc is known for "inhibiting the uptake" of dopamine, which means that dopamine stays around in your systems (brain) for a longer period of time. And, yes, more dopamine generally means better sex as I document in my link on Natural Dopamine Increasers . (Dopamine disorders are associated with migraines, Restless Leg Syndrome and other conditions.)
5. Depression. Zinc is a proven depression fighter. Several studies have shown that zinc levels tend to be lower in certain types of patients with depression and, furthermore, supplemental zinc has even been shown to help in treatment (25 mg along with an SSRI).  And, recently, researchers created depression (in animals) by inducing a zinc deficiency.
Of course, there is now a strong link established between Depression and Your Sex Life.
BONUS: Zinc can also significantly increase semen volume, something that some men are concernd about. For other factors, see my link Naturay Ways to Increase Your Semen Volume.
Zinc has some powerful properties that can really help us males. Because of this, it is very easy for to get overly enthusiastic. Zinc is extremely powerful and has a definite clinical range, i.e. you can hurt yourself if you overdo it in the ways listed below. Again, stick to the 1-2 RDA range for zinc.
CAUTIONS: Copper Deficincy: Some experts caution about taking zinc supplementation, because it can lead to a copper deficiency. Copper is critical for the health of your heart and your collagen among other things. It doesn't take much zinc to have a negative effect on your copper metabolism, because the two compete in the intestine for absorption. Researchers have found that it is the zinc to copper ratio that is critical and obviously taking zinc supplementation will affect this ratio significantly.
As an example, the RDA of zinc for an adult male is 11 mg and most zinc supplements have 2-3 times that, i.e. 20-35 mg or so. This is troublesome, because there is a disease (Wilson's Syndrome) where copper accumulates in various tissues. Researchers will actually give supplemental zinc in order to reverse this condition. How much zinc do they give? One study found that only 75 mg daily will quickly start depleting copper.  Remember that this 75 mg is intended to yield results in just 10 days.
Now imagine a guy taking 35 mg of zinc for testosterone for months or years. It is certainly possible that he could experience lowered copper levels and this could potentially lead to elevated inflammation and the steadily increasing hypertension associated with copper deficiency. Again, there is no study showing that this is occurring, but it is certainly possilble.
CAUTION: My HRT clinic, in guys whose estradiol is not too high, will use a combination of zinc (15-30 mg) and copper (2-4 mg) per day to pull down E2 (estradiol) levels a little. Zinc and copper compete and so many experts worry that giving supplemental could lead to copper depletion and inflammation. However, I have some concerns with this, because copper has been implicated in a number of neurological diseases and excesses are hard on neurons. These same experts believe that we are slowly poisoning ourselves in many cases with copper pipes. You'll have to do your own research and decide where you stand on the issue.
CAUTION #2: Neuron Damage. Before you go popping zinc like breath mints, keep in mind that some studies indicate that too much zinc is just as hard on your brain and neurons as too little. Most minerals have a rather tight range and zinc appears to be no exception.ï¿½
CAUTION #3: Heart Disease. There was a whole theory of heart disease that centered around the correct balance of copper to zinc.  Admittedly, this theory is outdated, but we can still learn something from it: too much zinc can elevate cholesterol levels and possibly contribute to hyperlipidemia. (You do not want too much copper either: it is very hard on the brain. When it comes to essential minerals, moderation and balance are definite keys.)
OTHER CAUTIONS: There are other potential risks in taking too much zinc, from neurotoxicity to cancer to metabolic issues and I summarize some of the latest research in my page on The Potential Dangers of Zinc Supplementation.
1) Med and Sci in Sports & Exerc,1999, 31:483
2) European J of Clin Nutr, 2009, 63:65-70
3) Intl J Sports Med,2001,22(7)537-543
4) Am J Med Sci, 1993 Apr, 305(4):199-202, "Treatment of Wilson's disease with zinc XII: dose regimen requirements"
5) J Nutr, 1996 Apr, 126(4):842-8, "Dietary zinc deficiency alters 5 alpha-reduction and aromatization of testosterone and androgen and estrogen receptors in rat liver"
6) Neuropharmacology, 2009, 56:531ï¿½540, "Zinc regulates the dopamine transporter in a membrane potential and chloride dependent manner"
7) Pol J Pharmacol, 2003, 55:1143ï¿½1147, "EFFECT OF ZINC SUPPLEMENTATION ON ANTIDEPRESSANT THERAPY IN UNIPOLAR DEPRESSION: A PRELIMINARY PLACEBO-CONTROLLED STUDY"
8) Journal of Neuroscience Research, 1 April 2005, 80(1):145-149, "Zinc modulation of serotonin uptake in the adult rat corpus callosum"
9) Physiol Behav, 2008 Oct 20, 95(3):365-9, "Zinc deficiency induces depression-like symptoms in adult rats"
10) Am J Clin Nutr July, 1975, 28(7):764-774, "Coronary heart disease: the zinc/copper hypothesis"
11) Biol Psychiatry. 1982 Apr;17(4):513-32, "Zinc, the brain and behavior"
12) Am J Clin Nutr July 1992 vol. 56 no. 1 148-157, "Effects of dietary zinc depletion on seminal volume and zinc loss, serum testosterone concentrations, and sperm morphology in young men"
15) 1) Systems Biology in Reproductive Medicine, 1981, 7(1):69-73, "Effect of Zinc Administration on Plasma Testosterone, Dihydrotestosterone, and Sperm Count"
16) J Hum Reprod Sci. 2010 Sep-Dec; 3(3): 124ï¿½128, "Relationship between seminal plasma zinc and semen quality in a subfertile population"