L-arginine is an amino acid, one of the building blocks of protein. It is classified as a “semi-essential” amino acid. The human body can synthesize a limited amount of L-arginine from other substances, sufficient to support basic metabolism. However, many individuals such as growing children, athletes, people under stress, sick people and aging persons cannot synthesize enough to meet their basic needs and may need to obtain supplemental L-arginine from the diet. L-arginine can be found in most protein-rich animal- or fish-based foods. Soybeans and nuts also contain some arginine. It is also widely available in over-the-counter supplements.
Function of L-arginine
Nitric Oxide and L-arginine
Nitric oxide is a small, simple molecule that is used by the body to stimulate blood vessels to dilate. Dilated blood vessels obviously allow for improved blood circulation to the relevant tissues. Nitric oxide is released and used locally to micro-regulate blood flow. A deficiency in the ability to produce nitric oxide (aka, not enough L-arginine) can cause systemic impairments in blood circulation.
Erectile Dysfunction

Sperm Quality

Hormones
Oral administration of L-arginine causes an increase in the production of human growth hormone. Administering human growth hormone to men can improve sperm quality quite significantly; in this particular study, 20 percent of infertile men treated with human growth hormone fathered children within one year. Human growth hormone also seems to have a global anti-aging effect on the body, improving vitality, sex drive and energy levels, all of which can certainly assist in improving fertility. However, a big problem with human growth hormone is that it has to be administered by daily injection, a major turn-off for most individuals. L-arginine can be taken orally.
L-arginine Safety
