Here are a few claims backed by research that we found:

Arginine has been linked to enhanced immunity, the release of the Human Growth Hormone, greater muscle mass, rapid healing from injury, increased sexual potency, and helping to reverse atherosclerosis [2]

Arthritis: Found in high concentrations in the connective tissues, arginine is a component of collagen that plays a vital role in the production of new tissue and bone cells. †

Cancer Patients: Arginine retards tumor growth by enhancing immune function. [3, 9] Arginine increases the size and activity of the thymus gland, which produces T-cells. Large doses of arginine can lower polyamines, which are present in various cancers in elevated levels. [1] Arginine has been found to inhibit the growth of several types of tumors in laboratory mice. †

Liver Disorders: Arginine aids in liver detoxification by neutralizing ammonia, and may benefit in the treatment of liver disorders such as liver injury, hepatic cirrhosis, and fatty liver degeneration. [1, 3, 9]

Weight Loss: Arginine facilitates a reduction in body fat, while increasing lean muscle mass. [3] Arginine inhibits the absorption of dietary fat. †

Body Building: More than fifty research studies reportedly support the value of arginine supplementation for athletes. [4] Arginine is considered to be key to efficient muscle metabolism because of its role in the transport, storage, and elimination of nitrogen. Creatine is derived from arginine, as are guanidophosphate and phosphoarginine, all of which have roles in muscle metabolism. †

Fertility: Seminal fluid contains substantial quantities of arginine, and arginine may be beneficial in treating sterility in men. [13] In one study, men with low sperm counts took 4 grams of arginine orally, with 80% of the men showing significant improvement, in some cases resulting in pregnancies. [9] Arginine is also noted by one researcher for its ability to increase libido and induce erections. [7,8] Arginine, ornithine, and aspartic acid have been shown to have a positive effect on sperm viability and motility. [1]

Anti-Aging Considerations:
Arginine is involved in the production of variety of enzymes and hormones. Arginine facilitates the release of HGH, stimulates the pancreas for insulin production, and is a component in the hormone vasopressin produced by the pituitary gland. [3] One mechanism for arginine as an HGH releaser may be its capacity for blocking secretion of the HGH-inhibitor: somatostatin. [8]

HGH-release by means of arginine may offer benefits in the treatment of fractures and injuries, as well strengthening the immune system, building lean muscle, burning fat, and reversing many of the effects of aging . [9]

The elderly respond to arginine with substantially increased levels of glucose and growth hormone. [1] A study at the Division of Endocrinology at the University of Turin involving normal adults aged 66-82 who tripled the level of HGH in their blood after administration of 30-gram injections of arginine. [4,8]

Arginine is essential for optimum growth and in the regulation of protein metabolism. [1] The main source of energy for muscle and other cells is glucose, but glucose metabolism produces ammonia, which is toxic unless rapidly converted to another compound. The primary metabolic role of arginine is in stimulating the enzyme that starts the urea cycle, which converts ammonia into a less toxic compound called urea that the blood carries to the kidneys for excretion. †

As a cholesterol fighter, a high ratio of arginine-to-lysine is recommended. [1] In the urea cycle, citrulline is a precursor of arginine, so it may be that foods rich in citrulline (onions, scallions, garlic) lower cholesterol because the citrulline is converted to arginine in the body. †

As a booster of the immune system , arginine stimulates the thymus and promotes lymphocyte production. [9,10] This may be the key to arginine's ability to promote healing of burns and other wounds. During stress (good or bad), the thymus gland typically shrinks, and sickness results; however, arginine facilitates the maintenance of the gland's proper size and normal production of lymphocytes. [15]

In support of brain function, arginine is believed to serve as a precursor to nitric oxide, a neurotransmitter. [1] Nitric oxide plays a role in the dilation and constriction of small blood vessels in brain. Therefore, arginine may have a positive effect on cerebral circulation. Arginine pyroglutamate is cited for having cognitive-enhancing effects. [16]

Related to its neurotransmitter function and its role as a precursor of nitric oxide, L-arginine has been noted for its critical role in stimulating healthy sex drive and enhanced sexual performance in men. [7] Taken in combination with pycnogenol, arginine has been reported to improve erectile dysfunction significantly. †

L-arginine's possible activity in wound repair may be due to its role in the formation of L-proline, an important amino acid that is essential for the synthesis of collagen. †

In summary, L-arginine is one of the most powerful tools in any anti-aging program because of its functional value in promoting the production of HGH and other hormones, strengthening the immune system, improving lean muscle mass and reducing fat, regulating several vital metabolic processes, improving cholesterol profiles, supporting brain function, and enhancing sexuality. Hundreds of studies have been undertaken to date, and clearly arginine merits further research. †

NOTES: Dietary L-arginine is found in plant and animal proteins, such as dairy products, meat, poultry, fish, and nuts. The ratio of L-arginine to lysine is also important - soy and other plant proteins have more L-arginine than animal sources of protein.
 
The L-form of arginine (and most other amino acids) is more compatible with human biochemistry. L-Arginine is classified as a conditionally essential amino acid, depending on the developmental stage and health status of the individual. Infants are unable to effectively synthesize arginine, making it nutritionally essential for infants. Adults, however, are normally able to synthesize arginine in the urea cycle.

Most researchers recommend the free forms of amino acids (powder form), which do not need to be digested and are absorbed directly into the blood for distribution throughout the body.

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CAUTIONS:
L-arginine should not be used following a heart attack.
L-arginine is also essential for children with rare genetic disorders that impair the formation of L-arginine.
A typical dose of arginine is 2 to 3 g of arginine per day.
For erectile dysfunction, a typical dose is 3 to 5 g per day. It takes approximately 3 to 4 weeks before results are noticeable.
L-arginine is conditionally essential, which means that the body normally has enough.
Severe burns, infections, and injuries can deplete the body’s supply of arginine. Under these conditions, L-arginine becomes essential and it is necessary to ensure proper intake to meet the increased demands.
L-arginine may counteract the benefits of lysine to treat herpes NSAIDS (non-steroidal anti-inflammatories) or other drugs that are hard on the stomach should not be combined with L-arginine. Drugs that alter potassium levels in the body, such as ACE inhibitors and potassium sparing diuretics. In large doses, L-arginine stimulates the release of hormones growth hormone and prolactin. Increased nitric oxide might be dangerous for people with certain medical conditions, such as kidney failure or cancer. And no one knows what’s the right dose or when it should be taken.
The toxicity level for amino acids is 50 to 500 times the therapeutic dose range. [1]
High-dose arginine supplementation may result in watery diarrhea and sometimes stomach cramps and headaches.
Individuals with herpes and other viral infections should not take arginine supplements, because arginine seems to promote the viral growth. [3, 17]
Persons diagnosed as having schizophrenia are advised to avoid dietary supplementation of arginine above 30 milligrams per day. [2, 3]
According to one physician, doses greater than 40 grams per day may pose dangers to patients with liver and kidney disease. [1] Another expert advises against any arginine for patients with liver and kidney disease without the permission of a physician. [9]
Arginine supplementation is not advised for pregnant women or nursing mothers [2], nor should supplemental amino acids be administered to a child. [3, 9]

References

[1] Braverman, M.D., E.R, The Healing Nutrients Within (New Canaan, CT: Keats Publishing, Inc., 1997), pages 18, 21-23, 212, 214, 219-221, 223, 228-229. ISBN 0-87983-706-3

[2] Cooper, M.D., M.P.H., Kenneth H., Advanced Nutritional Therapies (Nashville: 1996, Thomas Nelson, Inc. Publishers), pages 87-88, 93, 94. ISBN 0-7852-7302-6

[3] Balch, M.D., James F., and Balch, C.N.C, Phyllis A., Prescription for Nutritional Healing, Second Edition (Garden City Park, NY: 1997, Avery Publishing Group), pages 35-36. ISBN 0-89529-727-2

[4] Colgan, Ph.D., Michael, Optimum Sports Nutrition: Your Competitive Edge (Ronkonkoma NY: 1993, Advanced Research Press), pages 268, 330, 333-334. ISBN 0-964840-5-9

[5] Barbul, A. et al., Surgery, vol. 90, p. 244, 1981, as cited in Quillin, Ph.D., R.D., Patrick, Healing Nutrients (New York: 1989, Vintage), page 164. ISBN 0-679-72187-8

[6] Pearson, Durk and Shaw, Sandy, Life Extension: A Practical Scientific Approach (New York: 1980, Warner Books), pages 289, 612. ISBN 0-446-38735-5

[7] Lamm, M.D., Steven and Couzens, Gerald Secor, Younger at Last: The New World of Vitality Medicine (New York: 1997, Simon & Schuster), pages 62-64. ISBN 0-684-83438-3

[8] Klatz, D.O., Ronald with Kahn, Carol, Grow Young with HGH (New York: 1997, HarperCollins Publishers, Inc.), pages 200, 201, 206, 304. ISBN 0-06-018682-8

[9] Hendler, M.D., Ph.D., Sheldon Saul, The Doctor's Vitamin and Mineral Encyclopedia (New York: 1990, Fireside), pages 209-215. ISBN 0-671-66784-X

[10] Mindell, Ph.D., Earl, Earl Mindell's Anti-Aging Bible (New York: 1996, Fireside), pages 23-24. ISBN 0-684-81106-5

[11] Murray, N.D., Michael T. and Pizzorno, N.D., Joseph, Encyclopedia of Natural Medicine (Rocklin, California: 1991, Prima Publishing), page 359. ISBN 0-55958-091-7

[12] Le Vert, Suzanne, HGH: The Promise of Eternal Youth (New York: 1997, Avon Books), page 169. ISBN 0-380-78885-3

[13] Quillin, Ph.D., R.D., Patrick, Healing Nutrients (New York: 1989, Vintage), pages 274, 368. ISBN 0-679-72187-8

[14] DiPasqual, M.D., Mauro G., Body Building Supplement Review (no city listed: 1995, Optimum Training Systems), page 37.

[15] Visek, W.J., Journal of Nutrition, vol. 116, p. 36, Jan. 1986, as cited in Quillin, Ph.D., R.D., Patrick, Healing Nutrients (New York: 1989, Vintage), page 165. ISBN 0-679-72187-8

[16] Dean, M.D., Ward and Morgenthaler, John, Smart Drugs & Nutrients (Menlo Park: 1990, Health Freedom Publications), page 68. ISBN 0-9627418-9-2

[17] Whitaker, M.D., Julian, Dr. Whitaker's Guide to Natural Healing (Rocklin, California: Prima Publishing, 1996), page 269. ISBN 1-55958-495-5

Excerpted from the Vitality Research Institute at www.vitality-res.com and the U.C. Berkely Wellness Letter March 2005 at www.wellnessletter.com