Side Effects of Aspartic Acid

Many athletes turn to d-aspartic acid bodybuilding supplements to help them build more muscle. Although most studies have shown minimal d-aspartic acid side effects, studies are limited with virtually no knowledge of what — if any — long-term side effects exist.

Many athletes turn to D-aspartic acid bodybuilding supplements to help them build more muscle. (Image: itakdalee/iStock/GettyImages)

What Is Aspartic Acid?

Aspartic acid, or d-aspartic acid, is a non-essential amino acid. This means that your body produces an adequate amount of it without a need to supplement or get the amino acid from food sources. Some people, such as weight lifters and body builders, take supplemental amounts of d-aspartic acid in order to help build muscle mass.

However, body builders who take d-aspartic acid may not be actually helping their exercise routines. According to a small study of 24 participants published in April 2015 in the Journal of the International Society of Sports Nutrition participants who took 6 grams of d-aspartic acid saw a reduction in their total testosterone and free testosterone levels. Testosterone generally helps muscles grow, so a reduction in levels could hinder muscle growth.

An August 2017 study in PLOS One showed similar results. Physically active men showed a reduction in their testosterone levels. Raising their testosterone levels may build more muscle, so that means reducing testosterone levels may hinder muscle growth. Additionally they saw no significant improvement in their exercise performance when taking d-aspartic.

D-Aspartic Acid Sperm Effects

Men have also used d-aspartic acid for improving their fertility. There is limited, but promising, evidence that supports the use of d-aspartic acid for improving male fertility.

Though there isn't a lot of research, one smaller, older study showed some promise for the use of d-aspartic for boosting fertility. The study, published in October 2012 in Advances in Sexual Medicine, found that the 30 participants saw an increase in their sperm counts from taking d-aspartic acid.

Aside from increasing sperm count, the study showed an increase in sperm motility. This means that not only were there more sperm, but the sperm were also better able to move. This lead to more pregnancies in their partners.

Another much smaller study of 10 over weight men published in 2015 in the Open Nutraceuticals Journal also showed similar results. In their study, the overweight men took 3 grams of d-aspartic acid for 28 days. The results indicate an increase feelings of vitality and libido and also increased the subjects' testosterone levels in their blood.

D-Aspartic Acid Side Effects

There is limited research on d-aspartic acid. In the research, there is limited to no mention of side effects from participants who took supplements during the experiments.

For example, the same study published in October 2012 in Advances in Sexual Medicine looking at fertility issues found that of their 30 participants taking 3 grams of d-aspartic acid for 90 days reported no side effects. However, it does not know if there are side effects from long-term use.

Another older, smaller study of 10 men published in October 2013 in Nutrition Research found that 2 of the 10 (or 20%) experienced nervousness, headaches and irritability during the study. However, one member of the control group also noted similar side effects. And since the study is very small, it is impossible to say these side effects are accurate on a larger population of people.

According to the University of Rochester Medical Center, taking amino acid supplements can lead to some side effects. Some of the adverse effects they warn about are a negative nitrogen, which can impact your metabolism, and may cause your kidneys to work harder. They also warn that children should not take d-aspartic because it could affect their growth rate. Finally, they advise that pregnant and breastfeeding women should avoid the supplement.

Know that there is no safe upper limit or even recommended dosage for d-aspartic acid. However, most studies appear to use about 3 grams per day in their participants. If you decide to take d-aspartic acid you should only do so for a short time and follow the label's dosing instructions. If you notice any adverse effects, stop taking the supplement.

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