Study under review: The effects of d-aspartic acid supplementation in resistance-trained men over a three month training period: A randomised controlled trial
When people hear the term anabolic steroid, testosterone often comes to mind. This association makes sense—testosterone treatment can drastically increase muscle mass and strength without any other intervention in both healthy and hypogonadal adults. There is also a clear dose-response effect, meaning more testosterone leads to more muscle mass, although the effect is most pronounced when dealing with changes outside the normal range compared to within it. Essentially, if your goal is to build muscle and increase strength, then increasing testosterone levels is likely to help.
The sports supplement market has capitalized on young men’s drive for muscle gains. There are countless products available to buy that are claimed to boost testosterone levels. Many of these contain D-aspartic acid (DAA), an amino acid that has been shown to increase testosterone levels in rats through both direct actions on the testes and promoting the release of luteinizing hormone from the pituitary gland, which stimulates the testes to produce testosterone. DAA’s theoretical mechanism of action is summarized in Figure 1.
Initial research in humans was similarly promising. The first human trial to investigate the effects of DAA supplementation reported a significant 42% increase in testosterone levels when healthy men supplemented with three grams of DAA per day for 12 days. A follow-up study involving infertile men reported a significant 30-60% increase in testosterone levels with DAA supplementation (three grams a day for 90 days). However, two other studies involving resistance-trained young men found no effect on testosterone levels with three grams a day for 14 days or 28 days.
Of particular concern is that the 14-day study reported supplementing with six grams of DAA actually led to a significant reduction in free testosterone compared to placebo (-15% vs +9.4%). Not only does this finding not support the idea that DAA is a testosterone booster, it suggests that DAA might have the exact opposite effect if taken in higher doses. The study under review is a follow-up to this previous study by the same research lab. The goal of this study was to evaluate the effects on testosterone of supplementing six grams of DAA per day over a longer time—for 12 weeks—in healthy, resistance-trained men.
The supplement market is full of purported testosterone boosting supplements, such as D-aspartic acid (DAA). Animal and early human research has shown that DAA supplementation increases testosterone levels in both healthy and infertile men, but subsequent research in resistance-trained men reported no effect. One study even found that high doses of DAA (six grams a day) reduces testosterone levels over the short-term (two weeks). The study under review sought to evaluate the effects on testosterone of supplementing six grams of DAA per day over a longer time period (12 weeks) in healthy, resistance-trained men.
Other Articles in Issue #37 (November 2017)
Interview: Matt Stranberg, MA, RD, CSCS
In this interview, we chat with Matt about the utility of personal genomics for nutrition, how to keep up with nutrition research, what leads to successful dieting, and much more.
Interview: Mike Howard
Personal trainer and mindset performance coach Mike Howard shares his wisdom on how to stick with goals, his thoughts on Whole30, and more.
Vitamin D for athletes
Even athletes are subject to vitamin D deficiency. How much do they need to reach sufficiency, and does vitamin D supplementation have an effect on performance?
A whole (grain) in the evidence
Whole grain is thought to be heart healthy, mainly because of observational evidence. Are randomized controlled trials consistent with this recommendation?
Can riboflavin reduce muscle soreness?
Most research on riboflavin in athletics has focused on its effects on performance. Its effect on recovery are less well studied.
Can magnesium supplementation reduce cardiovascular disease risk factors in people with diabetes?
Observational, mechanistic, and animal evidence suggests that magnesium deficiency could raise the risk of CVD and diabetes. Could supplementation help?
Is exercise enough to improve the metabolic syndrome?
Diet and exercise combined can make an impact on factors of the metabolic syndrome. But could exercise by itself be enough to make a meaningful improvement?