Fortunately supplementation of Vitamin D3 has been noted to significantly boost testosterone levels up to 20%.[40,41] This occurs via a reduction in sex-hormone binding globulin (SHBG) and aromatase expression, which limits the breakdown of testosterone into estrogen. It’s also worth mentioning that Vitamin D3 has been shown to raise levels of the anabolic hormone IGF-1.[42,43]
There is a negative correlation of testosterone levels with plasminogen activator inhibitor-1 (PAI-1) (Glueck et al 1993; Phillips 1993), which is a major prothrombotic factor and known to be associated with progression of atherosclerosis, as well as other prothrombotic factors fibrinogen, α2-antiplasmin and factor VII (Bonithon-Kopp et al 1988; Glueck et al 1993; Phillips 1993; De Pergola et al 1997). There is a positive correlation with tissue plasminogen activator (tPA) which is one of the major fibrinolytic agents (Glueck et al 1993). Interventional trials have shown a neutral effect of physiological testosterone replacement on the major clotting factors (Smith et al 2005) but supraphysiological androgen administration can produce a temporary mild pro-coagulant effect (Anderson et al 1995).
The mineral zinc is important for testosterone production, and supplementing your diet for as little as six weeks has been shown to cause a marked improvement in testosterone among men with low levels.1 Likewise, research has shown that restricting dietary sources of zinc leads to a significant decrease in testosterone, while zinc supplementation increases it2 -- and even protects men from exercised-induced reductions in testosterone levels.3
If you're a man who's experiencing symptoms such as decreased sex drive, erectile dysfunction, depressed mood, and difficulties with concentration and memory, and you think low testosterone may be to blame, you can have your levels tested. Since testosterone levels fluctuate throughout the day, you'll probably need more than a blood test to get a true picture of your levels.
In a placebo-controlled study, 27 Division II football players received either a placebo or a ZMA supplement for a total of seven weeks during their scheduled spring practice. At the end of the seven weeks, the players taking the ZMA supplement had a 30 percent increase in testosterone, while the placebo group had a 10 percent decrease. The ZMA group also saw an 11.6 percent increase in strength, compared to only 4.6 percent in the placebo group.[7]

Tribulus terrestris is an ingredient commonly presented as improving testosterone levels, but has not been found to be more effective than a placebo or possess any testosterone increasing properties. WebMD cautions that it interferes with Lithium and diabetes medications, and in general, not enough is known about tribulus terrestris to recommend a dosage for anyone.

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Testosterone boosters are supplements used to improve workout performance, recovery, and the body’s natural ability to produce testosterone. T-Boosters are typically derived from herbs and other natural ingredients, so they’re generally safe to use in competition (Due to your own due diligence, however). What man on earth doesn’t want more testosterone? 
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Attention, memory, and spatial ability are key cognitive functions affected by testosterone in humans. Preliminary evidence suggests that low testosterone levels may be a risk factor for cognitive decline and possibly for dementia of the Alzheimer's type,[104][105][106][107] a key argument in life extension medicine for the use of testosterone in anti-aging therapies. Much of the literature, however, suggests a curvilinear or even quadratic relationship between spatial performance and circulating testosterone,[108] where both hypo- and hypersecretion (deficient- and excessive-secretion) of circulating androgens have negative effects on cognition.

Some of these signs and symptoms can be caused by various underlying factors, including medication side effects, obstructive sleep apnea, thyroid problems, diabetes and depression. It's also possible that these conditions may be the cause of low testosterone levels, and treatment of these problems may cause testosterone levels to rise. A blood test is the only way to diagnose a low testosterone level.