You're in your early twenties, and you're looking for a supplement that will boost your testosterone level and thus speed up your muscle bulking. Whatever you do, don't try D-aspartic acid. According to a small human study published by sports scientists Darryn Willoughby and Brian Leutholtz in Nutrition Research, the effect of D-aspartic acid on testosterone levels is minimal and the same goes for its effect on muscle strength.
After an Italian study showed that supplementation with 3 g sodium-D-aspartate boosted testosterone levels in elderly men, D-aspartic acid analogues became a modest rage in the sports supplements world. Experiences with pure D-aspartic acid were not particularly hopeful; those with calcium and sodium salts of the amino acid were better. The body absorbs these forms of D-aspartic acid better.
Willoughby and Leutholtz were sceptical about the D-aspartic acid rage. The men in the Italian study had low testosterone levels while bodybuilders generally have a high level as a result of heavy physical training and carefully worked out diets. So is D-aspartic acid effective in this group?
This is the question the researchers tried to answer by doing a 28-day long experiment with 20 recreational bodybuilders whose average age was 22.
The researchers gave half of their subjects 3 g D-aspartic acid daily. The other half of the subjects were given a placebo.
The supplement didn't work. The tables below show that the increases in testosterone level and strength were negligible. The effects were not significant at all.
The researchers observed that the supplementation only resulted in a limited rise in the subjects' D-aspartic acid level. What had risen significantly was the level of the enzyme D-aspartate oxidase – an enzyme that breaks down D-aspartic acid in the intestines, kidneys and liver.
So D-aspartic acid doesn't work, the researchers sum up. "We conclude that 28 days of D-aspartic acid supplementation at a daily dose of 3 g is ineffective in upregulating the activity of the hypothalamo-pituitary-gonadal axis and has no preferential effects in which to increase skeletal muscle mass and strength in resistance-trained men", they write.
This is the case for the free form of D-aspartic acid. The study has little to say when it comes to the sodium and calcium bound analogues of D-aspartic acid, sodium-D-aspartate and calcium-D-aspartate.
Nutrition Research. Available online 15 August 2013.