Arginine What does arginine do? The amino acid arginine has several roles in the body, such as assisting in wound healing, helping remove excess ammonia from the body, stimulating immune function, and promoting secretion of several hormones, including glucagon, insulin, and growth hormone. The effect of arginine on growth hormone levels 1 has interested body builders. In a controlled trial, when arginine and ornithine (500 mg of each, twice per day, five times per week) were combined with weight training, a greater decrease in body fat was obtained after only five weeks than when the same exercise was combined with a placebo.2 In another study, however, 5 grams of arginine powder, taken orally 30 minutes prior to exercise, failed to affect growth hormone release and may have even impaired the release of growth hormone in younger adults.3 Arginine is also needed to increase protein synthesis, which can in turn increase cellular replication. Therefore, arginine may help people with inadequate numbers of certain cells. For example, some,4 though not all,5 studies have found that men with low sperm counts experienced an increase in the number of sperm when they supplemented with arginine. Arginine’s effect on increasing protein synthesis improves wound healing. This effect has been shown in both animals6 and people (at 17 grams per day).7 Arginine is also a precursor to nitric oxide, which the body uses to keep blood vessels dilated, allowing the heart to receive adequate oxygen. Researchers have begun to use arginine in people with angina and congestive heart failure. Nitric oxide metabolism is also altered in people with interstitial cystitis, a condition of the bladder. Preliminary research found that supplementation with 1.5 grams of arginine per day for six months led to a significant decrease in most symptoms, including pain,8 though short-term supplementation (five weeks) has not been effective, even at higher intakes (3-10 grams per day).9 In 1999, a double-blind study using 1.5 grams of arginine for three months in a group of women with interstitial cystitis, reported considerable improvement compared with the effect of a placebo in a variety of indices. Perhaps due to the small size of the study, some of these changes did not quite reach statistical significance.10 Preliminary evidence suggests that arginine may help regulate cholesterol levels.1112 Arginine also appears to act as a natural blood thinner by reducing platelet aggregation. Where is arginine found? Dairy, meat and poultry, and fish are good sources of arginine. Nuts and chocolate also contain significant amounts of this amino acid.