6 g D-Aspartic Acid a day lowers testosterone levels

Evidence is mounting that D-Aspartic Acid supplementation does not raise bodybuilders’ testosterone levels. Researchers at the University of Western Sydney have confirmed that the eccentric amino acid doesn’t live up to expectations. In the human study they published in the Journal of the International Society of Sports Nutrition high doses of D-Aspartic Acid actually lowered the testosterone level.

D-Aspartic Acid Study

The Australians did an experiment with 24 young men aged between 18 and 36. The men had all been doing weight training for at least 2 years and could lift more than their own bodyweight on the bench presses.

The researchers divided their subjects into three groups of eight men. One group took a placebo for two weeks, the second group took 3 g D-Aspartic Acid daily and the third group took 6 g D-Aspartic Acid every day. [The structural formula of D-Aspartic Acid is shown above.] The subjects took the supplements with breakfast.

The 3-g dose of D-Aspartic Acid had no effect on the subjects’ testosterone level the researchers discovered. The 6-g dose did have an effect, but not what you’d expect: the supplement lowered the subjects’ testosterone level.


The researchers also measured the amount of estradiol and albumin in the subjects’ blood. D-Aspartic Acid had no effect on either of these.

“The need for longer-duration research utilising six grams of D-Aspartic Acid is clear”, the researchers summarised. “Future research should explore supplementation of 6 g D-Aspartic Acid per day over a longer period and observe any correlations between basal testosterone levels and changes in hypertrophy and strength.”

Three and six grams supplementation of d-aspartic acid in resistance trained men.


Although abundant research has investigated the hormonal effects of d-aspartic acid in rat models, to date there is limited research on humans. Previous research has demonstrated increased total testosterone levels in sedentary men and no significant changes in hormonal levels in resistance trained men. It was hypothesised that a higher dosage may be required for experienced lifters, thus this study investigated the effects of two different dosages of d-aspartic acid on basal hormonal levels in resistance trained men and explored responsiveness to d-aspartic acid based on initial testosterone levels.

Twenty-four males, with a minimum of two years’ experience in resistance training, (age, 24.5?±?3.2 y; training experience, 3.4?±?1.4 y; height, 178.5?±?6.5 cm; weight, 84.7?±?7.2 kg; bench press 1-RM, 105.3?±?15.2 kg) were randomised into one of three groups: 6 g.d(-1) plain flour (D0); 3 g.d(-1) of d-aspartic acid (D3); and 6 g.d(-1) of d-aspartic acid (D6). Participants performed a two-week washout period, training four days per week. This continued through the experimental period (14 days), with participants consuming the supplement in the morning. Serum was analysed for levels of testosterone, estradiol, sex hormone binding globulin, albumin and free testosterone was determined by calculation.

D-aspartic acid supplementation revealed no main effect for group in: estradiol; sex-hormone-binding-globulin; and albumin. Total testosterone was significantly reduced in D6 (P?=?0.03). Analysis of free testosterone showed that D6 was significantly reduced as compared to D0 (P?=?0.005), but not significantly different to D3. Analysis did not reveal any significant differences between D3 and D0. No significant correlation between initial total testosterone levels and responsiveness to d-aspartic acid was observed (r?=?0.10, P?=?0.70).

The present study demonstrated that a daily dose of six grams of d-aspartic acid decreased levels of total testosterone and free testosterone (D6), without any concurrent change in other hormones measured. Three grams of d-aspartic acid had no significant effect on either testosterone markers. It is currently unknown what effect this reduction in testosterone will have on strength and hypertrophy gains.

PMID: 25844073 [PubMed] PMCID: PMC4384294

Source: http://www.ncbi.nlm.nih.gov/pubmed/25844073