Abstract
BackgroundAlthough 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.MethodsTwenty-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.ResultsD-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).ConclusionsThe 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.
Highlights
Abundant research has investigated the hormonal effects of d-aspartic acid in rat models, to date there is limited research on humans
The primary findings of the current study were, 1) resistance trained men consuming six grams of d-aspartic acid daily demonstrated significant reductions in total and free testosterone after 14 days of d-aspartic acid supplementation, and 2) the responsiveness to d-aspartic acid supplementation was unaffected by initial testosterone levels in resistance trained men
Our results demonstrate that in resistance trained men three grams daily of d-aspartic acid had no significant effect on total testosterone, estradiol, sex-hormonebinding-globulin, and albumin
Summary
Abundant research has investigated the hormonal effects of d-aspartic acid in rat models, to date there is limited research on humans. In vitro rats studies demonstrated that DAA increased levels of testosterone, luteinizing hormone, progesterone [6] and growth hormone [10] This is believed to occur due to the accumulation of DAA in the anterior pituitary and testes [10]. Additional in vitro studies on isolated rat testes [6] and Leydig cells [11] indicate that DAA increased the rate of testosterone synthesis in a dose dependent manner. In these animals the maximal effective dose of DAA, which elicited the greatest hormonal response (LH, testosterone and progesterone), was 1 μmol.g−1 [6]. In humans the effects of different dosages of DAA on basal testosterone is unclear
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