Carnosine is a dipeptide compound composed of alanine and histidine. Carnosine is found in high concentrations in skeletal and heart muscles, and although no definite metabolic role has been ascribed to carnosine, it has been implicated in a variety of physiological processes. Perhaps the best-described function of carnosine is as a “broad-spectrum” antioxidant, where it has been shown to interact with several free-radical species, including singlet oxygen, hydrogen peroxide, and both peroxyl and hydroxyl radicals. In addition, carnosine is able to inhibit cellular damage induced by iron, copper, and zinc. Carnosine also appears to play a role in activating the enzymes responsible for generating muscle contractions (myofibrillar adenosine triphosphatase) as well as serving as an intramuscular buffering agent to retard accumulation of lactic acid. Of the potential therapeutic actions of carnosine, including antihypertensive effects, immune modulation, wound healing, and antitumor/ chemo preventive effects, there is some laboratory and preclinical evidence to suggest benefits, but most of these claims have not been convincingly documented nor subjected to rigorous clinical evaluation. Another possible benefit of carnosine is in the general area of “anti aging” because of the findings that carnosine levels may be reduced in concert with elevations in advanced glycosylation end products. If supplemental carnosine can reduce protein glycosylation, it may have therapeutic benefit in diabetes and other conditions in which glycosylated proteins lead to neuropathy and tissue dysfunction.

Given the potential physiological benefits of carnosine just outlined, its use as a dietary supplement is generally slanted toward sports nutrition, heart health, and anti aging. It’s possible roles in delaying fatigue, reducing stress, buffering acid buildup, healing wounds, improving muscle contraction, and protecting cells from oxidative damage tend to position carnosine as both an ergogenic aid and a general tonic. Unfortunately, much of what is known about carnosine is limited to laboratory and animal studies, and there is simply no convincing clinical evidence that dietary supplements containing carnosine can deliver anything beyond a modest antioxidant effect.

Carnosine is absorbed intact in the small intestine (jejunum) by a specific active transport mechanism. It circulates in the blood for transport to the kidney, liver, and muscle (where the highest concentrations are found). Carnosine is either used by these tissues or hydrolyzed (broken down) into alanine and histidine by the enzyme carnosinase found in the blood, liver, and kidney (Quinn et al, 1992).

As a water-soluble antioxidant, carnosine is capable of decreasing cell membrane oxidation caused by iron, zinc, copper, hydrogen peroxide, singlet oxygen, and both peroxyl and hydroxyl free radicals (Decker et al., 2000). The antioxidant effect of carnosine appears to be far greater than the individual or combined activity of its constituent amino acids, indicating that the peptide linkage between alanine and histidine is involved in some unique way in the overall antioxidant activity of carnosine (Quinn et al., 1992). In animal and test-tube experiments, carnosine has been shown to inhibit oxidation of LDL cholesterol and reduce development of breast cancer in rodents. High doses of carnosine may also possess some immune-stimulating activity, as shown by animal experiments in which very large doses of 50-200 mg/kg per day improved survival time by 50% in x-ray irradiated mice (Quinn et al., 1992). Carnosine appears to promote wound healing, as shown by animal experiments in which 6-20 mg/kg per day for 2 weeks reduced the size and depth of gastric ulcers and accelerated regeneration of the damaged tissue (Alabovskii et al., 1999).

In humans, we know that topical administration of carnosine (in the form of 1% N-acetylcarnosine in eye drops) is effective in treating cataracts (Babizhayev et al., 2002). Although much has been made in marketing material for carnosine-containing supplements (lactate-buffering capacity, carnosine capacity of muscle biopsies, etc.), there is a distinct lack of clinical data to support any of the many alleged benefits of oral carnosine consumption. One of the only published studies in humans shows that high-intensity exercise (strength or endurance training) has no appreciable effect on muscle carnosine concentration (Mannion et al., 1994).

Although no long-term safety studies have been conducted in humans, carnosine is not expected to result in any significant side effects when consumed at levels found in most commercial dietary supplements. Rodent experiments have noted no adverse toxic effects even at doses up to 500 mg/kg of body weight (about 35 g for an average-sized man). The average daily intake of carnosine from foods is probably in the range of 50-250 mg (based on a diet containing at least one serving, or 3-4 oz, of beef, pork, or chicken).

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