Low testosterone generally affects men in their later years, but some numbers indicate that the process of hormone decline can begin even earlier. In fact, as many as a quarter of men in their 30s, and almost half of those in their 40s, experience lower testosterone.
It’s no surprise, then, that a number of products have hit the shelves promising to increase testosterone. Many of these products promise their ingredients are backed by “clinical trials,” while neatly picking out one or two studies that vaguely prove their point.
I’ll be looking at one of those ingredients, D-Aspartic Acid, and looking to the whole body of literature to determine if there is merit to the claims that it can increase a man’s testosterone.
✲ Most studies, to date, with D-Aspartic Acid (DAA) dealt with animals; most of these data show a direct correlation between DAA and testosterone.
✲ Human studies have been rare, and their data inconclusive; some show net gains, some no gains, and some saw testosterone reductions.
✲ Inconsistency in human data may possibly be attributable to poor studies.
✲ Differences in results may correlate to other variables (ingredients taken with DAA).
What is D-Aspartic Acid?
Known chemically as an alpha (α) acid, Apartic acid comes in two forms, L- and D-. L-Aspartic acid is the one that forms with other amino acids to form protein chains. D-Aspartic acid’s uses and functions are less well known, but do take action during something called the urea process, performed by the kidneys and pertaining to waste.
Its role regarding testosterone is less clear. Well-researched projects have indicated evidence that DAA plays an important role in the cerebral (brain) development of mammals in the uterus, but that its presence tapers off near the end of pregnancy, and disappears nearly entirely by birth.
Majority of Studies
Sometimes numbers can be unintentionally misleading. The statement “Hundreds of studies show DAA increases testosterone” is factually true. But it leaves a lot of information out. Like the fact that over 300 of the 396 studies were conducted on animals.
And for the sake of clarity, many of these studies were conducted on human analogs, such as mice. Some, however, were also conducted on animals very distant from humans–such as frogs, and even female lizards.
These studies do overwhelmingly support the correlation between DAA and testosterone, by way of its presence in the brain, as previously noted. Animal studies have shown that DAA in-utero helps stimulate the hypothalamus and pituitary gland to produce testosterone. But the data has not necessarily translated to human trials.
I have reviewed dozens of literature analyses, human trials, and clinical studies, and in most of them the conclusions are that DAA has limited effect on men with low testosterone. In trained male athletes there is no effect. And in doses higher than recommended, it may have a feed-back triggering effect, where the body actually produces less testosterone.
I have included here five studies. There were another four with similar results, in the same ratio (half failures, half success), but their data and findings didn’t offer any context not represented here.
One study of men in Italy had participants ingest DAA with vitamins B6 and B12, along with folic acid (this is a proprietary blend in Europe). According to researchers, they found an increase in testosterone and something called the luteinizing hormone (a hormone that triggers the production and distribution of other ‘sex’ hormones).
Another team of researchers wanted to know if there were physiological implications of DAA, and they set about to measure the sperm motility and health of men taking DAA. Their results found increased numbers, swim speed, and swim strength of men taking DAA, as well as higher blood levels of testosterone and luteinizing hormone. One interesting note, this study was led by a scientist from the previous study. This is not in and of itself a disqualifier, but is worth mentioning.
In contrast to the Italian research, scientists publishing in the journal Nutrition Research conducted a 28 day, placebo controlled study of men undertaking weight training. In the study, both groups of men had statistically increased testosterone, both produced by the testes and the pituitary gland–but the increases were not significant between the two groups of men.
Two interesting points about this study, though, are that their hypothesis was that DAA would not work, and their raw data is not available. That means it is entirely possible there was a sizable difference in testosterone levels between placebo and DAA group, but not rising to the level of statistically important.
Another study yielded more mixed results, with some men showing testosterone over 20% higher than baseline. But this study is flawed by several factors: it was not blind (participants knew they were taking DAA, leading to a possible placebo-effect); it was very small (only 10 men); and the DAA was taken with other ingredients (sodium nitrate and vitamin D3).
Lastly, we have perhaps the best-run of all the studies. Their data are fully visible and their methods were sound. In it, they had healthy, actively exercising men randomly assigned to either placebo or DAA groups. The data show that after treatment, the men had lower testosterone after taking DAA, especially at higher doses (6 grams/day). Researchers have hypothesized this may be the body shuts down the process of testosterone production because of signal overload.
What it All Means
Perhaps the most frustrating factor to consider when it comes to these data is that we have far more pertaining to animals than humans. Second most frustrating is that the effects of D-Aspartic Acid in animals seems to be compellingly sound: it does indeed increase testosterone.
It remains to be determined if the factors limiting the human studies can be overcome or designed around. For instance, it could be that the studies without successes are because D-Aspartic Acid only works in men with low testosterone; or it could be that there are other factors that make DAA more effective.
But until such time as many more robust studies are conducted, it seems that there is little reliable evidence that DAA can or will increase testosterone in men.