d-Aspartic acid is a an amino acid that's contained in many foods and also sold as a dietary supplement. D-aspartic acid acts as a neurotrasmitter or neuromodulator. Aspartic acid is important in the development of nervous sytem. It is also a component of transmitters that send nerve impulses between nerve cells. Aspartic acid increases cAMP levels (a signal transporter between the cell surface to inside the cell). Aspartic acid also plays a role in the neuroendocrine system, as a regulator in the synthesis and release of hormones.
In the pituitary gland, aspartic amino acid stimulates the secretion of the following hormones:
- Prolactin, a hormone known to stimulate mammary glands and milk production, among other functions.
- Luteinizing, a hormone which is involved in the reproductive system. In males it plays role in testosterone synthesis; where as in females, it plays role in ovulation and the menstrual cycle.
- Growth hormone (GH).
d-Aspartic acid is mainly present in some glands, such as the testicles, as well as in semen and sperm cells. Studies showing that d-Aspartic acid supplements may increase levels of testosterone that plays an essential role in male fertility.
A study in infertile men suggested that taking 2.66 grams of d-Aspartic acid for three months increased their testosterone levels by 30–60%. Another study in healthy men showed that taking 3 grams daily for two weeks increased testosterone levels by 42%.