D-Aspartic Acid (DAA) 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 .
Recommended Dosage & Usage
A typical recommended dosage of DAA for testosterone boost is 3 grams (or exactly 3,12 grams as this exact dosage has been used in a study where testosterone increase in humans has been noted ) daily. Some companies ever recommend taking this dose 2 times daily.
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 from 4 and up to 12 weeks followed by a period of cessation from the product lasting 2 to 4 weeks.
Rich natural sources of D-aspartic acid are :
- Soy Protein
- Soy Based Infant Formula
- Zein (corn protein)
- Mediterranean bivalve mollusks 
D-Aspartic Acid Hormonal Interaction
Nowadays, almost every “good” testosterone booster has D-aspartic-acid on its list (usually listed on the very top just in case you don’t miss it). But is it really that effective?
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. MAny newer studies reported that despite its role in testosterone production, supplementing DAA fails to boost testosterone, muscle building or exercise performance.
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 sedentary men were given a daily dose of 3,12 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 in the number of spermatozoa and of their motility. Researchers haven’t noted any abnormalities in serum measurements indicating D-Asp does not cause any damages to the health.
This early research in humans showed promising increases in testosterone levels and based on that testosterone boosters are now filled with DAA. The problem was that these human studies were carried out on infertile and sedentary men. Willoughby & Leutholtz  recruited resistance trained men for their study which exhibited a higher average baseline testosterone count compared to sedentary men. After 29 days of supplementation with 3.000 grams of DAA per day and resistance training, levels of total testosterone and free testosterone were not affected. Rodgers et al.  gave a D-Pol™, a testosterone booster which contains 3.12 grams of DAA, sodium nitrate and Vitamin D3, to 24 resistance trained men. No significant changes were observed in total testosterone or other hormones tested. Geoffrey William Melville  further examined DAA dosages in well-trained males in his doctoral thesis. Participants were assigned to either to placebo, three grams of DAA and six grams of DAA groups. The critical finding of the dosing study was that resistance trained men consuming a daily dose of six grams of D-aspartic acid demonstrated significant reductions in total (~12.5%) and free testosterone (~15.3%) after 14 days of D-aspartic acid supplementation. In a group receiving three grams daily of D-aspartic acid, there was no significant effect on total testosterone, estradiol, sex-hormone-binding-globulin, and albumin. He theorised that 6 g/d may be affecting negative feedback mechanisms of the HPG axis, thus reducing pituitary initiated production of luteinizing hormone and in turn testosterone levels. It is also possible that D-aspartic acid is over-accumulating within the testes creating a disruptive effect. Since one of the limitations of this study was its short duration (14 days) scientist decided to make a 3-month long follow-up study. The key findings of this study were that 6 grams of DAA did not increase or decrease testosterone levels in resistance-trained men and that both groups had similar strength and mass gains.
Similarly, the methylated form of DAA (N-methyl-D-aspartate – NMDA; which can also be synthesised from DAA) failed to elevate endogenous testosterone levels and increase muscle mass or strength after 28 days of supplementation in combination with resistance training .
It seems that with resistance training, there is a natural upregulation of DAA which is negating any potential benefit from exogenous supplementation. Furthermore, Willoughby & Leutholtz  reported no group differences in serum DAA, but significant increases in serum DAA oxidase (DDO); an enzyme known to degrade DAA. Suggesting increased DDO activity is degrading DAA faster than it can accumulate within tissues.
There is no clinical evidence to support the claim that DAA boosts testosterone, builds muscle or has any ergogenic value. Currently, positive effects of supplementation have been observed in men with infertility issues and relatively low baseline testosterone. While the long-term consequences of its consumption in a resistance trained population are currently unknown.
There are some claims that D-aspartic acid supplementation may increase estrogen  however there are no serious studies to back that up. In fact, supplementation of 3 g D-aspartic acid in trained athletes for 28 days failed to affect circulating estrogen levels , while another study reported a decrease .
Melville et al.  were the first to examine changes in the H-reflex pathway following a period of resistance exercise in trained men. Results are rather shocking as in the placebo group improved excitability of the H-reflex pathway was observed while it was weakened in DAA group. Researchers speculated that since DAA appears to fit the role of a neurotransmitter, DAA is inhibiting the capacity of the neurotransmitter system to adapt over time to the resistance exercise stimulus. DAA can enter a neuron via L-glutamate transporters and higher doses than normal might be saturating them. This may, in turn, result in blunted neural adaption.
Consuming about 3g D-aspartate for 90 days seems to be well tolerated without reported abnormalities in electrolytes, liver enzymes, glucose, urea, creatinine, and both red and white blood cell function . Long-term studies have not yet been performed using D-aspartic acid.
(Other common names: Aspartic Acid, L-Aspartate, L-Aspartic Acid, D-Asp, N-Methyl-D-Aspartic Acid, NMDA)
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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.
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- Want Romance? Oysters May Really Work – WebMD.com Retrieved at 6. May 2013
- Willoughby, Darryn S., and Brian Leutholtz. “D-Aspartic acid supplementation combined with 28 days of heavy resistance training has no effect on body composition, muscle strength, and serum hormones associated with the hypothalamo-pituitary-gonadal axis in resistance-trained men.” Nutrition research 33.10 (2013): 803-810.
- Melville, Geoffrey W., Jason C. Siegler, and Paul WM Marshall. “The effects of d-aspartic acid supplementation in resistance-trained men over a three month training period: A randomised controlled trial.” PloS one 12.8 (2017): e0182630.
- Man, Eugene H., and Jeffrey L. Bada. “Dietary D-amino acids.” Annual review of nutrition 7.1 (1987): 209-225.
- Rodgers, Logan J., et al. “Impact of a Multi-Component Dietary Supplement on Blood Testosterone, Nitrate/Nitrite and Physical Performance in Resistance-Trained Men.” (2016).
- Melville, Geoffrey William. Effects of d-aspartic acid on testosterone and training outcomes in a resistance trained population: findings from an acute dosing study, and a three-month training study. Diss. Western Sydney University (Australia), 2016.
- Willoughby, Darryn S., Mike Spillane, and Neil Schwarz. “Heavy resistance training and supplementation with the alleged testosterone booster NMDA has no effect on body composition, muscle performance, and serum hormones associated with the hypothalamo–pituitary-gonadal axis in resistance-trained males.” Journal of sports science & medicine 13.1 (2014): 192.