D-AA is an amino acid that is seen as a regulator of Testosterone metabolism. It appears supplementation may be able to increase testosterone in men, and the release of hormones such as growth hormone or LH from the hypothalamus.
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D-Aspartic Acid is one of the two forms of the amino acid Aspartic Acid (sometimes referred to as Asparate depending on pH), with the other form being L-Aspartate. The benefits associated with D-Aspartate are unique to it, and do not apply to L-Aspartate and only minimally to dietary Aspartic Acid (due to low concentrations of D-Aspartate).
D-Aspartate is essentially a neurotransmitter and a stimulant, as well as a precursor to another neurotransmitter and stimulant (NDMA). It works in a central brain region to cause a release of hormones such as Luteinizing Hormone, Follicle-Stimulating Hormone, and Growth Hormone secondary to acting on receptors directly. D-Asparate may also build up in the testicles, where it alleviates a rate-limiting step of Testosterone synthesis and thereby increases testosterone levels minorly.
There are minimal human studies on the subject matter, and minimal interventions at all. The majority of information is assessing the roles D-Aspartate has in the body under normal conditions, and does not consider supplementation.
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D-AA, D-Aspartate, DAA
DL-Aspartate, Aspartate
Testosterone increasing benefits have been found with taking 3000mg (3g) once daily.
D-Aspartic Acid, like all Testosterone Booster, should be cycled. The two main cycle lengths seem to be:
12 days on, followed by 7 days off; repeat if desired
3 weeks on, followed by 2-4 weeks off; repeat if desired
The former was used in the lone human study, the latter has been used with success anecdotally. Whether cycling is needed with D-Aspartic Acid is unknown but currently prudent.
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The Human Effect Matrix looks at human studies (excluding animal/petri-dish studies) to tell you what effect D-Aspartic Acid has in your body, and how strong these effects are.
| Grade | Level of Evidence |
|---|---|
| A | Robust research conducted with repeated double blind clinical trials |
| B | Multiple studies where at least two are double-blind and placebo controlled |
| C | Single double blind study or multiple cohort studies |
| D | Uncontrolled or observational studies only |
| Level of Evidence | Effect | Change | Magnitude of Effect Size | Scientific Consensus | Comments |
|---|---|---|---|---|---|
| C | Testosterone |   Notable | 100% See study | Notably effective in comparison to other testosterone boosting nutraceuticals, but still not overly potent. | |
| D | Fertility | Minor | 100% See study | Appears to be effective in increasing male fertility, but requires more evidence | |
| D | Sperm Quality | Minor | 100% See study | Appears effective, needs to be compared against a comparator. |
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D-Aspartic Acid is one of the enantiomers of the amino acid known as Aspartate, where the common dietary enantiomer is L-Aspartate. 'Aspartic Acid' and 'Aspartate' are similar stuctures with asparate being the conjugate base of Aspartic Acid, and interconversion occurring depending on the pH of the solution. The D and L refer to the direction to molecule bends light (with D-isomers bending light to the right, and L-isomers bending light to the left) and for all intents and metabolic purposes can be considered different bioactive molecules, molecules that differ only in their ability to bend light (those denoted with a D or a L, like L-Carnitine) are known as enantiomers, and a mixture of both enantiomers is called a 'racemic' mixture.
Naturally occurring alternate form of one of the main 20 structural amino acids
D-Aspartic Acid can be found naturally occurring in the diet, with rich sources being (and the percentages referring to how much Asparate is racemized in the D-enantiomer):
D-Aspartate can also be created (racemized) from L-Asparate during the process of cooking or heating, and it has been reported that a doubling of D-Asparate may occur in raw milk during the pasteurization process (from 1.5% to 3%).[2]
Co-exists alongside L-Asparate, may be racemized based on the stimul presented to the amino acids with heat being most implicated in turing L-Asparate into D-Asparate
L-Aspartate is non-essential amino acid and can be incorporated into protein structures, although D-Aspartate is not commonly associated with protein structures.[3] D-Asparate has been found to be a constituent of human cartilage,[4] enamel,[5] and can be accumulated in the brain[6] as well as being a constituent of red blood cell membranes.[7]
Asparate is a non-essential amino acid, and the D-isomer is not commonly used for structural proteins. It is more of a signalling molecule than anything
The distribution of D-Aspartate in the mammalian brain is, for humans, around 20-40nmol/g wet tissue[3] with a higher content of around 320-380nmol/g in the brain of an embryo.[8] One study comparing normal brains against persons with Alzheimer's and found no differences in grey matter, with twice the accumulation in white matter.[9] Interestingly, concentrations of D-Asparate in the hippocampus (dentate gyrus and CA1) are lower in older humans than they are in younger humans which may have roles in memory formation.[10]
In rats, overall concentrations are fairly similar (15-30nmol/g wet tissue) with higher concentrations in the pituitary (120–140nmol/g) in pituicytes,[11][12] pineal gland (650–3000nmol/g) in pinealocytes of the posterior pituitary,[13][14] and to a lesser extent the retina (30-60nmol/g)[15] and in the supraoptic and paraventricular nuclei of the hypothalamus, where the axons of these neuronal clusters end up in the pituitary.[16] Outside of the brain, D-Aspartic Acid builds up in the elongate spermatids of the testicles,[17][18] where the concentrations of D-Aspartate can form up to 60% of all Aspartate and is second only to the pineal gland for highest concentration.[19]
D-Aspartic Acid can be produced endogenously from the amino acid L-Aspartic Acid, via the enzyme Asparate Racemase.[20]
D-Aspartic Acid can get methylated via the enzyme D-Aspartic acid methyl-transferase to become the neurotransmitter NMDA (N-methyl-D-Aspartate), and uses S-Adenosyl Methionine (SAMe) as the primary source of the methyl group.[21] NMDA is an agonist for a subset of glutamate (excitatory) receptors in the brain with a wide range of effects as neuromodulators.[3]
NMDA and D-Aspartate are both metabolized by the enzyme D-amino acid oxidase.[22]
D-Aspartate, via its metabolites NMDA, is an excitatory neurotransmitter. This seems to be present all across the brain, but to a higher extent in the pituitary and pineal gland
D-Aspartic acid has been shown (in boar testes) to be able to upregulate the aromatase enzyme, which increases localized production of estrogens.[23] This has also been noted in lizard testes as well.[24][25]
Upon depolarization of a neuron, D-Aspartate is released into the synapse in a Ca2+ dependent manner where it can stimulate a neuronal transmission post-synaptically; indicating that D-Aspartate per se is an endogenous neurotransmitter without needing to be converted to the more well known metabolite NMDA.[26] Release has been noted in astrocytes[27] and rat brain slices[10] particularly the hippocampus[28][29] in response to K+ stimulation as well.
D-Aspartate can also be substrate to produce the more well known neurotranmistter NMDA (N-methyl-D-Asparate) via accepting a methyl group from a donor, and both NMDA as well as D-Asparate itself can act with similar potency on NMDA receptors.[30]
Is both a storage form for an excitatory neurotransmitter, as well as being a neurotransmitter itself
Administration of 40mM Sodium-D-Asparate daily for 12-16 days was able to enhance neuronal funtion and memory in rats by increasing their ability to find a hidden platform in a Morris Maze test, decreasing the required time from 20-30s to 5+/-2s.[31]
This study calculated oral dose being 60mg daily per rat, and 0.19mg/g daily, and caused no noticeable side-effects after one month of treatment. This dose also increased total D-Aspartate concentrations of the brain from 30.6+/-5.4nmol/g wet weight to 82.5+/-10nmol/g after 18 days of treatment, it specifically increased hippocampus levels of D-Asparate by 2.7fold on average, and hippocampal concentrations of D-Asparate correlated with improved performance.[31]
Preliminary evidence suggests that D-Aspartic Acid via oral ingestion is a cognitive enhancer
The enzyme that converts L-Asparate to D-Asparate, Asparate Racemase, has been implicated in regulating neurogenesis in adults secondary to producing D-Asparate.[20] This study that abolished the enzyme that creates D-Aspartic Acid in vivo notes that newborn neurons had significantly reduced dendritic length and arborization (branching), where neurons inable to produce D-Aspartic Acid had 40% the length of controls and up to 50% more cellular death.
D-Aspartate may be taken up into Testicles via the NMDA receptors, present in both Leydig and Sertoli cells of the testes.[32] After being taking up into a cell, D-Aspartate appears to have the ability to induce testosterone release, although it tends to work synergistically with hCG by increasing the efficacy of hCG on a testicular cell.[33] This increase in testoterone synthesis is not seen after 1 hour of incubation (yet is after 16 hours), and can both increase cholesterol transport into the inner mitochondrial membrane by increasing expression of the StAR protein, which is a transporter that brings cholesterol into the mitochondria and is also influenced by Cordyceps.[33] hCG treatment is able to increase expression of StAR itself via a cAMP dependent pathway,[34][35] and incubation of a cell with D-Asparate can increase hCG-induced StAR mRNA upregulation 3.5-fold and protein content by 1.9-fold and can increase in cAMP levels by 3.1-fold at 0.1mM and 5.25-fold at 5.25mM.[33]
Increasing activity of the rate-limiting step in steroidogenesis (steroid synthesis) in the testes may underly the ability of D-Aspartic Acid to increase testosterone in otherwise healthy men, which has been noted once
Oral intake of 500mg/kg and 1g/kg are associated with increases of 12 and 20% of 3β-HSD, respectively, in rats.[36]
Nitric Oxide (NO) is increased by 30% at 500mg/kg, but fails to be increased at 1g/kg in rats.[36]
D-Aspartic Acid may have the ability to induce oxidative stress in the testes, where 500mg/kg and 1g/kg bodyweight D-Aspartic Acid in rat feed, but not 50mg/kg bodyweight, caused oxidative stress in the testes over the course of 7 days.[36] At this dose, the weight of the testes (and liver) are slightly decreased by 11-13% and oxidative markers increased at the 500mg/kg and 1g/kg dose by 74% and 85% (mitochondria) and 30% and 46% (cytosol), and according increases were seen in lipid peroxides.[36] These pro-oxidative changes were met with an increase in Glutathione, Glutathione Transferase, and Catalase without changes in SOD as well as adverse alterations in mitochondrial function as measured by increase of Ca2+ influx and a decrease in mitochondrial membrane potential.[36]
In vitro, these pro-oxidative effects are concentration-dependent and start to occur at 250uM in the cytosol yet occurred at much lower concentrations in the mitochondria (5-50uM causing a two-fold increase).[36]
Higher doses of 500-1,000mg/gk in rats are associated with preliminary toxicological signs, and this dose correlates to 80-160mg/kg in humans; an oral dose of 7.2-14.4g for a 200lb human
Beyond the testes and testosterone synthesis, D-Asparate appears to be involved with spermatogenesis (production of sperm) and may have a role in reproduction due to its correlations.[37] One human study using 2.66g D-Aspartate daily for 90 days in men with abnormal seminal profiles (asthenozoospermia and oligoasthenozoospermia) noted improvements in seminal motility and concentration (ranging from 50-100% improvements from baseline) and was associated with higher fertility rates in men.[38] This study also noted a significantly higher D-Aspartate concentration in the semen of men given D-Aspartate (96-100% higher concentrations).[38]
D-Asparate may have a role in female sexuality and reproduction, as it has been detected as a physiological component of follicular fluid and its levels decline with age, the decline of which is correlated with the decline in reproductive potential.[39]
Activation of receptors on the hypothalamus may precede hormonal release from the pituitary gland, as blocking NMDA receptors in the preoptic area of the anterior hypothalamus (that D-Asparate and its metabolite NDMA signal vicariously through) can reduce testosterone.[40]
The hypothalamus also appears to be a neuroorgan implicated in the memory enhancing effect of D-Asparate, as supplementation of 0.16mg/g to mice has shown to increase cognition and performance increases were correlated with hypothalamic D-Asparate concentrations.[31]
There is approximately seven-fold higher in the anterior pituitary than the posterior pituitary,[12] where in the posterior pituitary it is spread fairly evenly over an area expressing neuronal axons while in the anterior pituitary it is concentrated in the cytoplasm of endocrine cells.[41] In the anterior pituitary, D-Asparate may accumulate in prolactin-producing cells or similar as levels are enhanced by estrogen implantation and both D-Aspartate concentration and the cell count are higher in females.[12][41] It is possible that these cells produce D-Asparate endogenously as injection of D-Asparate is not taken up[42] and a tumor-strain of prolactin producing cells has been noted to synthesize D-Asparate.[43]
In the pituitary, D-Aspartate is involved in inducing Prolactin secretion.[3] Injections of D-Asparate at 0.5-4M/kg induce a release or Prolactin in rats in a dose-dependent manner from 1.9-fold (0.5M) to 3.7-fold (4M) measured 30 minutes after injection,[44] this was thought to be mediated via NMDA-mediated activation following uptake into the anterior pituitary.[44]
D-Asparate is highly localized in the pituitary, and may be synthesized locally as well; here, it is involved in a neurohormone release pattern. Injections are associated with increased prolactin, and this has not been explored in humans
Accumulation of D-Aspartic Acid (and NMDA) in the Adenohypophysis (Anterior Pituitary) causes increases in the secretion rates of Gonadotropin releasing hormone (GnRH), Growth-Hormone releasing hormone (GHRH), and Prolactin Releasing Factors (PRFs) which cause releases of Luteinizing hormone (LH) and Follicle-Stimulating Hormone (FSH), Growth Hormone (GH), and Prolactin, respectively.[21]
In the pineal gland, the neuroorgan where D-Asparate reaches its highest neuronal concentrations, D-Asparate acts as a regulatory factor for Melatonin secretion.[45] This study initially incubated norephinephrine at 10uM with pinealocytes and confirmed that melatonin was synthesized in response to NE, and that this synthesis was abolished when D-Asparate was incubated, dropping to 20% of control at 0.2mM and acting through a receptor-mediated Gi/Adenyl Cyclase inhibitory pathway in the pinealocyte.[45] L-Asparate also has the ability to supress melatonin synthesis,[46] but at the same concentration is a tad weaker.[45]
D-Aspartate appears to be synthesized in the pineal glands (which does express Asparate Racemase,[26] but may more likely sequester D-Asparate from outside the cell[41]) and then secreted out of the cell via a sodium dependent glutamate/asparate transport present on pinealocytes that responds to D-Asparate,[47] and then acts on receptors coupled with inhibitory Gi receptors to inhibit Melatonin synthesis.[45][48] D-Asparate can later be resequestered via transporters such as GLT-1[49] back into the pinealocyte to prevent excessive signalling, and as such is a regulating factor of melatonin synthesis.
It is currently unknown whether supplemental D-Aspartic Acid can influence these processes.
D-AA is involved with the circadian rhythm of Melatonin, stored in the pineal glands and secreted when melatonin synthesis needs to be suppressed. Practical significance is unknown
D-Aspartic Acid causes increases in testosterone synthesis via upregulation of the mRNA that produces a compound called STAR (Stimulating steroidogonic Acute Regulatory Protein) which regulates androgen synthesis in the Leydig cells.[50]
The secretion of hypothalamic LH (from the neurally active excess of NMDA) also induces testosterone synthesis in the leydig cells and may be mechanism by which D-Aspartic Acid influences testosterone synthesis.[17][11]
It has been found to increase testosterone levels in humans.[19] This study used a product called DADAVIT, which is Sodium-D-Asparate, and in 23 males over a period of 12 days a testosterone spike was experienced in 20 persons (87%) which also appeared to be the amount of people responding to a Luteinizing Hormone spike. Testosterone rose 42% when measured at 12 days, from a baseline average of 4.5+/-0.6 to 6.4+/-0.8 ng/ml, and was only 15% above baseline when measured at 6 days and 22% above baseline 3 days after cessation, which is thought to be from D-Aspartic Acid accumulation in the testes.[19] Another study conducted with 2.66g D-Asparate in subfertile men noted that, after 90 days, that serum testosterone was a variable 30-60% higher when each subject was compared to their own baseline.[38]
Following consumption of 2.66g D-Asparate for 90 days in subfertile men, there were no reported abnormalities noted in serum measurements.[38] This study measured electrolytes, liver enzymes, glucose, urea, creatinine, and both red and white blood cell function.
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