D-Aspartic acid is a naturally occurring, endogenous amino acid that is found in nervous and endocrine tissues of the human body. In the body D-aspartic acid is formed when the enzyme aspartate racemase converts L-aspartic acid into D-aspartic acid in the testes and other glands.
D-aspartic Acid is a clinically backed sports and nutrition supplement that is designed to dramatically boost an athletes testosterone level. It is an amino acid found naturally in the body and it works its magic by increasing the production of the messenger hormone Luetenizing Hormone(LH) and the muscle building hormone  testosterone in the pituitary gland and the testes, by enhancing the cellular production of signal molecules that control the output of LH and Testosterone. In studies DAA was shown to increase the concentration of cGMP in the pituitary gland.  cGMP is a signal molecule, also known as a second messenger, that transfers messages in the pituitary cells from other messenger hormones to the DNA. More cGMP means more LH, which is a very good thing. In the testes D-aspartic acid plays a similar role with the signal molecule cAMP, via which D-aspartic acid increases testosterone secretion.
DAA plays a key role in the manufacture of sperm cells and sex hormone. DAA is used in many pharmaceuticals such as the Italian Pharmaceutical product Dadavit, which is aimed at infertile men.
A popular study showing the effects of DAA on testosterone levels was carried out by one of these pharmaceutical companies and in the research study 24 men between the ages 27 and 37 were given a daily dose of 3.12g D-aspartic acid for 12 days consecutively. 24 other men were given placebos. The testosterone level in the men that received the DAA had risen by 33% after only twelve days!