Ornithine is an amino acid produced by the breakdown of arginine, another amino acid. This breakdown occurs during the citric acid cycle, which is a part of the human waste expellation process. During this cycle, L-aginine interacts with the enzyme arginase to create both ornithine and urea. Ornithine is not an essential amino acid, and plays no part in protein synthesis. Since it is non-essential, the human body can generate it without an outside source.
Humans rarely have a deficiency of this acid. Meat, fish, and dairy products are all excellent sources of the compound, and the human body needs very little of it to function. Only five to ten grams of this amino acid are required per day for proper body function, and a typical daily Western diet typically includes approximately five grams of this substance. Supplements are rarely needed for dietary reasons, and ingesting more than ten grams per day can cause intestinal distress.
In the body, ornithine is needed to create proline and citrulline, both of which are essential in supplying energy to cells. This acid is also speculatively linked to an increase in growth hormone and insulin levels, both of which help build muscle. For this reason, ornithine supplements are often marketed to bodybuilders. Common wisdom holds that ornithine is twice as effective as arginine at stimulating growth hormone levels, and supplements that contain both compounds are considered redundant. It is important to note that no human trials have been conducted to verify the link between muscle growth and this amino acid.
The acid is also used medically to treat patients after surgery, or those who have suffered trauma. A compound known as ornithine alpha-ketoglutarate (OKG), has been tested in several studies, and patients who used it reported faster healing, along with an increase in appetite, over those who did not. Also, this compound has been shown to assist in burn recovery. Taking 10-30 milligrams (mg) of OKG after a severe burn resulted in both shorter hospital stays and increased healing for patients.
Another compound, ornithine aspartate, has been used to treat patients with liver cirrhosis who have also developed brain abnormalities. A double-blind study was conducted, in which some patients were given 18 grams of ornithine aspartate per day, while other received a placebo. Those taking the drug showed significant improvement in liver function after two weeks as compared to those who did not recive the supplement.