D-Aspartic acid (DAA, D-Asp) is an endogenous amino acid which has been found in the neuroendocrine tissues of both invertebrates and vertebrates . It occurs in a high concentration in the pineal gland  and is implicated in the α-melanocyte-stimulating hormone, GABA, and is involved in luteinizing hormone, testosterone  and dopamine release .
Testosterone increase with D-aspartic acid
Previous studies have demonstrated that D-aspartic acid is involved in the synthesis and release of sexual hormones. In the light of this, it was hypothesized that D-aspartate plays an important role in steroidogenesis.
In an Italian study , aimed to evaluate the effects of D-aspartate administration on luteinizing hormone (LH) and testosterone production in humans and rats, a group of 23 men were given a daily dose of 3 grams D-Aspartate (Dadavit®) for 12 days, whereas another group of 20 men were given a placebo. After 12 days of D-aspartic acid treatment the levels of testosterone and luteinizing hormone of the participants were significantly increased (approximately 40 percent). Three days after the suspension of D-aspartic acid treatment, testosterone was still significantly increased (10% drop).
G. D’Aniello, et al.  reported 30-60% higher serum testosterone in subfertile men after 90 days of D-Aspartic acid supplementation (2.66g) compared to their own baseline. They also demonstrated that D-aspartate induces a significant increase of the number of spermatozoa and of their motility. Researches haven’t noted any abnormalities in serum measurements indicating D-Asp does not cause any damages to the health.
Raul A. Mirza and colleagues sought to determine the concentrations of D-aspartic acid and N-methyl-D-aspartate (NMDA) in the most consumed Mediterranean bivalve mollusks. Analysis of the chemical composition of tissue samples taken from different types of mollusks showed D-Asp and NMDA were present in three varieties of clams. These two compounds have been shown in animal studies to stimulate the release of hormones, including testosterone and estrogen. Researchers concluded that it plausible that the presence of D-Asp and NMDA in these mollusks could correlate with aphrodisiac properties of these mollusks. 
D-aspartic acid usage recommendations
Long-term studies have not been performed using D-aspartic acid. Most manufacturers of products containing D-aspartic acid recommend cycling the product. Which means a period of usage up to 12 weeks followed by a period of cessation from the product lasting 2 to 4 weeks. Since studies show D-aspartic acid supplementation may also increase estrogen , and estrogen blocker should be added.
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- D’Aniello, Gemma, et al. “D-Aspartate, a Key Element for the Improvement of Sperm Quality.” Advances in Sexual Medicine 2.4 (2012): 45-53.
Pampillo, Macarena, et al. “The effect of D-aspartate on luteinizing hormone-releasing hormone,[alpha]-melanocyte-stimulating hormone, GABA and dopamine release.” Neuroreport 13.17 (2002): 2341-2344.
- Topo, Enza, et al. “The role and molecular mechanism of D-aspartic acid in the release and synthesis of LH and testosterone in humans and rats.” Reprod Biol Endocrinol 7 (2009): 120.
- Want Romance? Oysters May Really Work – WebMD.com Retrieved at 6. May 2013