D-Aspartic Acid and Testosterone: A Review on Benefits and Side Effects

D-AA and Testosterone: Scientific Review on Benefits & Side-Effects

D-Aspartic Acid is a very common ingredient in test booster supplements. Companies claim that it is "scientifically proven" to work. But if you know anything about the supplement industry, you know that it's very easy for companies to make technically correct statements (using petri-dish and animal studies) that don't carry on to affect our bodies in the same way. 

In this article, I will go over the 5 human trials that studied the interaction between D-AA and testosterone, as well as my analysis of them. 

TL;DR: D-AA supplementation seems to increase testosterone levels in the short-term (6-12 days). Although this increase may persist in infertile men, T-levels return to baseline within a month or so in otherwise healthy men.

What is D-Aspartic Acid?

D-Aspartic Acid is an alternate form of the amino acid known as Asparate.

Amino acids are the building blocks of protein, and Asparate is one of the 20 main structural amino acids. 

D-AA is naturally present in the human body, primarily in the pineal and pituitary glands. The pituitary is the area of your brain that triggers the production of anabolic hormones.

D-AA has been shown to increase the secretion of Gonadotropin releasing hormone (GnRH) which, in turn, increases the release of Luteinizing hormone (LH) (1). LH is the precursor for testosterone synthesis, which is why D-AA supplementation has been theorized to increase T-levels in the body. 

Rat studies have shown D-AA injections to increase testosterone levels by up to 300% (2), but this does not mean that the same effect carries on to humans as well.

Does D-AA Increase Testosterone In Humans​?

After scrounging the web, I was able to find five human studies that observed the interaction between D-AA supplementation and testosterone. My aim with the rest of this article is to go over each of these trials so that you can know for sure whether D-AA actually boosts testosterone or not.

Human Trial #1

The Role And Molecular Mechanism Of D-aspartic Acid In The Release And Synthesis Of LH And Testosterone In Humans And Rats

Effect

Increase

Trial Design

Double blind

Trial Length

12 days

Number of Subjects

43

Gender

Male

Body Type

Healthy 

Methods

43 healthy men (without ED), aged 27-37, were given a daily dose of either 3.12 grams of D-asparate or placebo for 12 days.

Blood samples from each participant were collected at 6 days of treatment, 12 days of treatment, and 3 days after the treatment ended. 

Results

12 days after treatment, the men receiving D-asparate experienced, on average, a 33% increase in LH and a 42% increase in total testosterone levels. 

3 days after the treatment was over, LH levels dropped by ​14% and total T by about 9%. 

My takeaway: D-AA seems to have potent testosterone-boosting properties in the short-term; a 42% increase in 12 days is no joke. 

Effect

None

Trial Design

Double blind

Trial Length

28 days

Number of Subjects

20

Gender

Male

Body Type

Resistance-trained

Methods

​Resistance-trained men received a daily dose of either 3g of D-aspartic acid or placebo over the course of 28 days. During this time, they were also put on a 4-day/week resistance-training program. 

Body composition, muscular strength, and anabolic hormone measurements were taken once before the experiment began and once at the 28-day mark. 

Results

Researchers found that all the variables measured remained relatively the same across both groups. They concluded that D-AA supplementation is not associated with increases in muscular strength or anabolic hormone concentrations. 

My takeaway: Compared to Human Trial #1 (which lasted only 12 days), this study took place over 28 days. So although D-AA supplementation may boost testosterone over the short term, the effect does not seem to prolong past the 28-day mark.

Effect

Increase

Trial Design

Cohort

Trial Length

90 days

Number of Subjects

60

Gender

Male

Body Type

Infertile

Methods

60 infertile men were split into two groups based on their sperm quality:

  1. Oligo-asthenozoospermia (reduced sperm motility and low sperm count)
  2. Asthenozoospermia (reduced sperm motility)

Sperm motility refers to how well the sperm in a given semen sample are moving. ​Sperm count is measured as the amount of sperm/mL of semen. 

Each man was given a daily dose of 2.66g of D-aspartic acid over the course of 90 days.

Semen samples were collected by masturbation; once before D-AA supplementation and once at the 90-day mark. Blood samples were also collected.

Results

In oligo-asthenozoospermic patients, D-AA supplementation increased total sperm count by 52% and sperm motility by 78%. 

In asthenozoospermic patients, D-AA supplementation increased total sperm count by 57% and sperm motility by 81%. 

Another interesting finding of the study was an increased pregnancy rate in the partners of the treated patients by 26.6%. 

Also, LH and testosterone levels increased between 30-60%. 

My takeaway: D-AA supplementation seems to be very effective at increasing fertility and testosterone levels in infertile men.

Effect

None

Trial Design

Double blind

Trial Length

14 days

Number of Subjects

15

Gender

Male

Body Type

Healthy

Methods

15 healthy men (average age=22) were randomly assigned to ingest a daily dose of either 3g of D-AA or placebo over the course of 14 days. ​

Blood samples were taken once before the experiment and once at the 14-day mark. ​

Strength measurements, ​as the 1-rep maximum on bench press and squat, were also recorded. Once before and once after 14 days of D-AA supplementation. 

Results

The subjects given D-AA experienced increased levels of strength (3% stronger on bench press and 5.6% stronger on squat), while placebo did not. 

Testosterone levels across both groups, however, remained relatively unchanged.  

My takeaway: Another study that shows no interaction between D-AA supplementation and testosterone levels in otherwise healthy men. Although strength did increase in the D-AA group, it did not increase by much.

Effect

Decrease

Trial Design

Double blind

Trial Length

4 weeks

Number of Subjects

24

Gender

Male

Body Type

Resistance-trained

Methods

24 resistance-trained men (aged 21-28) were randomly assigned to three experimental groups: 1) placebo, 2) 3g of D-AA, 3) 6g of D-AA. 

All participants were put on a 4-day/week resistance training program for the full month. 

Supplementation was introduced during the final two weeks of the experiment. 

Blood samples were collected at three intervals; once before the experiment began, once at the 2-week mark, and once at the 4-week mark. 

Results

The subjects supplementing with 6g of D-AA experienced a 12.5% decrease in total testosterone and a 15.3% decrease in free testosterone. 

The subjects supplementing with 3g of D-AA experienced a 0.7% decrease in total testosterone and a 2% decrease in free testosterone.

The placebo subjects experienced a 0.7% increase in total testosterone and a 9.4% increase in free testosterone.​

My takeaway: The fact that the control group experienced the best results in this experiment is surprising. Based on the results of this study, it seems like D-AA supplementation has a negligible effect on testosterone and that using too much of it can actually cause a decrease. 

The Bottom Line: D-Aspartic Acid Is Not a Proven Testosterone Booster

Out of the five human trials, only two of them showed D-AA supplementation to increase testosterone levels. Of these two, one experiment lasted only 12-days while the other was carried out in infertile men. The other three showed no significant interaction between D-AA and testosterone. 

So if D-AA is not a proven testosterone booster, why do companies continue to add it in their supplements?

It's because the supplement industry is not highly regulated. This makes it very easy for them to make grand claims that are not really true. 

On the surface, D-AA seems to be a powerful testosterone booster. After all, it is naturally present in the brain and has been shown (in petri-dish and test-tube studies) to stimulate LH production. But when the experiments are run on humans, the results are not so significant. The supplement companies choose to leave that part out. 

D-AA For Bodybuilding

Based on Trial #2 cited above, 28-days of D-AA supplementation had no effect on muscle growth. Nor did it have any effect on power output, as assessed by leg press and bench press 1-rep maximum measurements. 

Trial #4 showed D-AA supplementation to increase strength on the leg press and bench press, but even then the extent was negligible. 

Does D-AA Have Any Benefits?

Based on the research, the only situation where D-AA supplementation seems to provide any benefits is in the case of fertility. 

For infertile men, D-AA supplementation seems to have tremendous benefits in terms of improving sperm quality and increasing testosterone levels.

In otherwise healthy men, D-AA can increase testosterone levels within a 2-week time span, but over the long-term there don't seem to be any benefits. ​

D-AA Side Effects

In doses under 4 grams, there are very few reported negative side-effects of D-AA supplementation. 

In some rare cases D-AA supplementation has led to acne, digestive issues, irritability, mood changes, and headaches. 

(source)

The Down and Low On D-Aspartic Acid

D-AA is perhaps, after Tribulus Terrestris, the most common ingredient added to testosterone booster supplements. But just because you read that it is "scientifically proven" to boost testosterone levels doesn't mean that it will do so in every situation. Context is always important, which is why, even with the research, it is valuable to observe how many subjects were involved in the experiment, over how long did the experiment take place, and what factors led to the certain results. 

In the short-term (up to 2 weeks), D-AA supplementation can increase testosterone levels. Although this positive interaction may last longer in infertile men, the effect in otherwise healthy men is diminished past the 14-day mark. 

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