D-aspartic acid (DAA) is an amino acid and an isomer of L-aspartic acid (LAA), which is one of the 23 amino acids encoded by DNA that synthesize proteins in humans.
DAA is found in the human body and various foods, but in much smaller amounts that its counterpart LAA.
Despite its minimal production in the brain, DAA appears to play a significant role in our neuroendocrine system, especially with regards to the production of male sex hormones, androgens, and growth factors.
In recent years, supplementation with DAA has garnered interest for athletic performance enhancement.
Read on as we take a look at the science behind DAA and its use for boosting testosterone levels.
It should also be noted that aspartic acid and its base, aspartate, are biologically identical in many regards so the acronym ”DAA” will refer to both forms.
The production of testosterone (and many other hormones) is controlled by an intricate feedback system between the hypothalamus, pituitary gland, testes (called the HPTA axis) and the liver.
As you can see from the diagram below, the HPTA has an innate negative feedback loop that suppresses the secretion of hormones such as GnRH (gonadotropin releasing hormone), LH (luteinizing hormone) and FSH (follicle-stimulating hormone), which in turn prevents testosterone from increasing.
Contrarily, increases in GnRH lead to increases in LH and FSH levels which go ultimately on to stimulate the production of testosterone.
Moreover, GH and IGF-1 are also regulated by the HPTA axis. When the hypothalamus produces growth hormone-releasing hormone (GHRH), the pituitary releases GH in a pulsatile fashion. GH then goes on to signal the liver to produce IGF-1.
With this simple grasp of how these hormones are produced in males, let’s take a look at how DAA can impact their production.
Several studies in animals suggest that DAA works by stimulating luteinizing hormone-releasing hormone (LHRH) in the hypothalamus, which tells the pituitary to secrete LH. [1,2,3]
This effect appears to be mediated by neurons in the hypothalamus and anterior pituitary gland that have neural nitric oxide synthase (nNOS), as a study showed that the effects of DAA on LHRH were blunted when NOS is inhibited.
Thus, NO is ultimately what tells the hypothalamus to produce LHRH (note that NO production in other parts of the body doesn’t affect LHRH production). Interestingly, the neurotransmitter gamma-aminobutyric acid (GABA) inhibits NO production in the brain, which makes sense since DAA inhibits GABA production.
This is a curious finding as though as it could suggest that compounds/supplements that increase GABA in the brain (like phenibut) may be a bad idea for testosterone production.
It is also suggested that DAA may actually also stimulate the production of thyroid hormones, specifically T4 and T3. 
It is hypothesized that this occurs from the oxidation of DAA in the thyroid gland to hydrogen peroxide, a necessary precursor for the iodination of tyrosyl compounds (which is essential for the synthesis of thyroid hormones).
At the time of this article, many of these benefits are based on anecdotes, animal studies, and suppositions.
Keep in mind that animal studies and anecdotes don’t necessarily translate completely to how compounds will act in most humans.
The unfortunate case for DAA is that human studies on DAA intervention remain scarce (and the few studies that do exist appear rather underwhelming). 
Anecdotal evidence has been positive in some individuals, and negative in others, who supplement with DAA, so further studies will certainly be helpful. Factors to consider that could alter the response to DAA include age, endocrine health, training status, diet, etc.
That being said, here are some of the most reported benefits of DAA use:
Testosterone, GH, and IGF-1 all have implications for speeding up the recovery time from resistance training, enhancing muscle growth, increasing work capacity, and libido, among other factors for the active individual.
However, it should be noted that increases in testosterone within physiological ranges, as seen with DAA supplementation, appear to have minimal effect on healthy males.
This is to say that unless you’re producing less-than-nominal amounts of testosterone, the benefits of DAA may not be significant.
DAA use, even in the short-term, can induce a variety of side effects that may override many of its benefits when all is considered. These side effects include:
Some individuals that may benefit from DAA supplementation include:
NOTE: It is wise to have your testosterone levels overseen by a licensed medical physician prior to and throughout your time supplementing with DAA.
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