D-Aspartic Acid




D-Aspartic Acid (D-Asp) has received a lot of attention in the strength training world for claims that it can raise testosterone levels. Research has found that D-Asp can increase testosterone but there is a lack of convincing evidence from studies done on humans.  After reviewing the literature, the question remains, is it worthwhile to take this supplement or are you better off making sure your magnesium, omega-3, and essential amino acids levels are at their best?

What is D-Aspartic Acid?
D-Asp is an endogenous amino acid and is found in the neuroendocrine tissues of humans. There is evidence that D-Asp plays a role in sperm production and that it is involved in the release of testosterone (T), growth hormone (GH), and luteinizing hormone (LH). It also modulates melatonin synthesis and is found in high concentration in the pineal gland. In boars and lizards D-Asp has also been shown to enhance the conversion of testosterone to estrogen.
What Ergogenic Effect Does D-Asp Have in Humans?
In men, D-Asp has been found to improve motility of sperm and raise T levels. In an Italian study, after supplementing with a 20 mM solution of D-Asp (about 3 grams of D-Asp) for 12 days, 87 percent of the subjects had significantly increased LH and T levels  (from 4.5 ng/ml serum to 6.4 ng/ml) by 33 and 42 percent, respectively.
Researchers point to the fact that six days into the dosing protocol, T was only slightly elevated, whereas after 12 days it was significantly higher and stayed higher for three days after stopping the supplementation. This was thought to be due to evidence that when supplementation is suspended, D-Asp levels are maintained for at least three days in the testes, continuing to trigger T production. A study conducted on rats at the same time, indicated that D-Asp regulates the synthesis of LH from the pituitary and T from the testes. This hormone response is mediated in the pituitary by cGMP and in the testis by cAMP.
Further support for D-Asp is seen with a recent study that gave a supplement of pycnogenol (60 mg/d), l-arginine (690 mg/d), and aspartic acid (552 mg/d) to Japanese patients with erectile dysfunction. Taking the supplement for eight weeks improved sexual function and increased testosterone slightly. The aspartic acid supplement was small, which may be one of the reasons there was only a small T increase.
What Can We Take From This Research?
Due to a lack of studies done on humans, it’s probably best to stay skeptical about the benefits of D-Asp. The one study from 2008 hasn’t been replicated on humans and additional evidence isn’t currently available. Once more peer approved research has been done, given it is now 2013, we will report it here