Before you take L-Carnosine, you will want to read this:
MIRACULOUS, LIFE-EXTENDING NUTRIENT OR NEUROTOXIN?

The dipeptide, carnosine, composed of two linked amino acids, histidine and beta-alanine, occurs naturally only in meat products, has been recently promoted in some publications for the treatment of disorders that may range from neurological degeneration to brain circulatory deficit.
The studies described were performed on cell culture experiments, i.e. cells grown in bottles away from a living being, or in rodents. After reading these articles, one may have the notion that taking carnosine is a prerequisite for health, youth and longevity.
It must be considered that every coin has two sides ...
Aspartame (NutraSweet), is also a two amino acid peptide (dipeptide) that has been used to sweeten foods and drinks, however, today we know that it may be a dangerous neurotoxin, causing numerous neurological symptoms and disorders.
So, what about carnosine?
In the real biomedical world carnosine is significant when the HUMAN body is unable to detoxify itself of it, i.e. break it down. This simply means, when there is an accumulation of carnosine, serious, even life threatening neurological diseases may set in. This condition is referred to as
CARNOSINEMIA

Carnosinemia is of established biomedical recognition and significance. The condition simply is carnosine overload perpetrated by either a genetical defect due to a lack of production of the detoxifying enzyme carnosinase, or it can occur from the inhibition of the enzyme by too much of its substrate, carnosine.
Saunders DICTIONARY & ENCYCLOPEDIA OF LABORATORY MEDICINE AND TECHNOLOGY, ed. J.L. Bennington, W.B. Saunders and Company, 1984, p.262 defines, "carnosinemia, an inherited condition, transmitted as an autosomal recessive trait, that is characterized by the presence of excessive amounts of carnosine in the blood and urine. Caused by genetic deficiency of the enzyme carnosinase (aminoacyl-histidine dipeptidase), carnosinemia results in progressive neurological damage, severe mental retardation, and myoclonic seizures," as found in Alzheimer's and progressive myoclonous epilepsy, Jacob-Creutzfeldt disease (mad cow or spongy brain diseases), subacute sclerosing panencephalitis, closed head trauma, and hypoxic-ischemic brain injury.
A more current reference, TIETZ TEXTBOOK of CLINICAL CHEMISTRY, ed. C.A. Burtis and E.R. Ashwood, W.B. Saunders Company, 1999, p. 452 describes, "carnosinemia, carnosinase deficiency, excessive amounts of carnosine in the blood and urine, also excessive amount of homocarnosine in the urine, with clinical features of severe neurological disease with no effective treatment."
It should be realized that an overload of substrate, i.e. carnosine in the present case, will cause the inhibition of the degradation/detoxifying enzyme, carnosinase. As a result, there will be an accumulation of high concentrations of carnosine in the blood and tissues. This carnosine accumulation is the same as induced carnosinemia and potentially, in time it may cause many of the deleterious effects described above.
Scientists reported a reduced carnosinase activity in patients with Parkinson's disease, multiple sclerosis, and patients following a cerebrovascular accident, Wassif WS, Sherwood RA, Amir A, Idowu B, Leigh N, Petres TJ, Serum Carnosinase Activities in Central Nervous System Disorders, Clin Chim Acta 1994 Feb;225(1): 57-64.
Might there be a correlation between carnosine overload and these neurological disorders?

As a conclusion, those who are presently taking carnosine may, in fact, induce the potentially dangerous neurotoxic condition, carnosinemia. Therefore, it is not advisable to supplement with carnosine. In the light of all of the above, one can see one of the true benefits of a vegetarian diet. Patients with neurological disorders such as M.S., Parkinson's Disease, A.L.S. and Alzheimer's Disease could very well benefit from a vegetarian diet.
Dr. E.K. Schandl

M.S., Ph.D., FACB, SC(ASCP), CC(NRCC), LNC, CLD, Clinical Laboratory Director, Oncobiologist Clinical/Nutritional Biochemist