Testosterone is a well-known hormone that’s responsible for muscle building and libido. People of all ages are looking for natural ways to increase this hormone, and one popular method is to take dietary supplements that claim to boost testosterone. These products often contain the amino acid D-aspartic acid.
This article explains what D-aspartic acid is and whether it increases testosterone.
What Is D-Aspartic Acid?
Amino acids are molecules that have several functions in the body. They’re the building blocks of all types of protein, as well as certain hormones and neurotransmitters. Almost every amino acid can occur in two different forms. For example, aspartic acid can be found as L-aspartic acid or D-aspartic acid. The forms have the same chemical formula, but their molecular structures are mirror images of each other (1).
Because of this, the L- and D- forms of an amino acid are often considered “left-handed” or “right-handed.” L-aspartic acid is produced in nature, including in your body, and used to build proteins. However, D-aspartic acid isn’t used to build proteins. Instead, it plays a role in making and releasing hormones in the body (1, 2, 3).
D-aspartic acid can increase the release of a hormone in the brain that will ultimately result in testosterone production (2). It also plays a role in increasing testosterone production and release in the testicles (3, 4). These functions are the reason why D-aspartic acid is popular in testosterone-boosting supplements (5).
SUMMARY: Aspartic acid is an amino acid found in two forms. D-aspartic acid is the form involved in testosterone production and release in the body. Because of this, it is often found in testosterone-boosting supplements.
Effects on Testosterone
Research on the effects of D-aspartic acid on testosterone levels has yielded mixed results. Some studies have shown that D-aspartic acid can increase testosterone, while other studies have not.
One study in healthy men aged 27–37 examined the effects of taking D-aspartic acid supplements for 12 days (6). It found that 20 out of the 23 men taking D-aspartic acid had higher testosterone levels at the end of the study, with an average increase of 42%. Three days after they stopped taking the supplement, their testosterone levels were still 22% higher, on average, than at the beginning of the study.
Another study in overweight and obese men taking D-aspartic acid for 28 days reported mixed results. Some men had no increase in testosterone. However, those with lower testosterone at the beginning of the study experienced increases exceeding 20% (7).
Another study examined the effects of taking these supplements for longer than a month. The researchers found when men aged 27–43 took supplements of D-aspartic acid for 90 days, they experienced a 30–60% increase in testosterone (8).
These studies did not specifically use a physically active population. However, three other studies did examine the effects of D-aspartic acid in active men. One found no increase in testosterone in young adult men who performed weight training and took D-aspartic acid for 28 days (5). What’s more, another study found that two weeks of taking a high-dose supplement of 6 grams per day actually decreased testosterone in young men who weight trained (9). However, a three-month follow-up study using 6 grams per day showed no change in testosterone (10).
Similar research in women is not currently available, perhaps because some of the effects of D-aspartic acid are specific to the testicles (4).
SUMMARY: D-aspartic acid may increase testosterone in inactive men or those with low testosterone. However, it has not been shown to boost testosterone in men who weight train.
It Does Not Improve Response to Exercise
Several studies have examined whether D-aspartic acid improves the response to exercise, particularly weight training. Some think it may increase muscle or strength gains due to increased testosterone levels.
However, studies have shown that men performing weight training experienced no increases in testosterone, strength or muscle mass when they took D-aspartic acid supplements (5, 9, 10). One study found that when men took D-aspartic acid and weight trained for 28 days, they experienced a 2.9-pound (1.3-kg) increase in lean mass. However, those in the placebo group experienced a similar increase of 3 pounds (1.4 kg) (5). What’s more, both groups experienced similar increases in muscle strength. Thus, the D-aspartic acid didn’t work any better than the placebo in this study.
A longer, three-month study also found that men who exercised experienced the same increase in muscle mass and strength, regardless of whether they took D-aspartic acid or a placebo (10). Both of these studies concluded that D-aspartic acid is not effective at increasing muscle mass or strength when combined with a weight-training program.
No information is currently available about combining these supplements with other forms of exercise, such as running or high-intensity interval training (HIIT).
SUMMARY: D-aspartic acid does not appear to improve muscle or strength gains when combined with a weight training. No information is currently available regarding the effects of using D-aspartic acid with other forms of exercise.
D-Aspartic Acid May Increase Fertility
Although limited research is available, D-aspartic acid shows promise as a tool to help men who are experiencing infertility. One study in 60 men with fertility problems found that taking D-aspartic acid supplements for three months substantially increased the number of sperm they produced (8). What’s more, the motility of their sperm, or its ability to move, improved.
These improvements in sperm quantity and quality appear to have paid off. The rate of pregnancies in the partners of the men taking D-aspartic acid increased during the study. In fact, 27% of the partners became pregnant during the study.
Although much of research on D-aspartic acid has focused on men due to its supposed effects on testosterone, it may also play a role in ovulation in women (11).
SUMMARY: Although more research is needed, D-aspartic acid may improve the quantity and quality of sperm in men with infertility.
Most studies examining the effects of D-aspartic acid on testosterone have used doses of 2.6–3 grams per day (5, 6, 7, 8, 9). As discussed earlier, research has shown mixed results for its effects on testosterone. Doses of around 3 grams per day have been shown to be effective in some young and middle-aged men who were likely physically inactive (6, 7, 8). However, this same dose has not been shown to be effective in active young men (5, 9).
Higher doses of 6 grams per day have been used in two studies without promising results. While one short study showed a decrease in testosterone with this dose, the longer study showed no changes (9, 10).
The study that reported beneficial effects of D-aspartic acid on sperm quantity and quality used a dose of 2.6 grams per day for 90 days (8).
SUMMARY: A typical dose of D-aspartic acid is 3 grams per day. However, studies using this amount have produced mixed results. Based on the available research, higher doses of 6 grams per day do not appear to be effective.
Side Effects and Safety
In one study examining the effects of taking 2.6 grams of D-aspartic acid per day for 90 days, researchers performed in-depth blood testing to examine whether any adverse side effects occurred (8). They found no safety concerns and concluded that this supplement is safe to consume for at least 90 days.
On the other hand, another study found that two of 10 men taking D-aspartic acid reported irritability, headaches and nervousness. However, these effects were also reported by one man in the placebo group (5). Most studies using D-aspartic acid supplements did not report whether side effects occurred.
Because of this, it is possible that more research is needed to confirm its safety.
SUMMARY: Limited information is available concerning any potential side effects of D-aspartic acid. One study showed no safety concerns based on blood analysis after 90 days of using the supplement, but another study reported some subjective side effects.
The Bottom Line
Many people are searching for a natural way to boost testosterone. Some research has shown that 3 grams of D-aspartic acid per day can increase testosterone in young and middle-aged men. However, other research in active men has failed to show any increases in testosterone, muscle mass or strength. There is some evidence that D-aspartic acid may benefit sperm quantity and quality in men experiencing fertility problems. While it may be safe to consume for up to 90 days, limited safety information is available. Overall, more research is needed before D-aspartic acid can be strongly recommended for boosting testosterone.