Lysine

High dietary intake of protein can elevate lysine, as well as lack of cofactors needed in its utilization and catabolism, such as thiamine and niacin. 

Hyperlysinemia is a rare inborn error of metabolism that causes a defect in the major catabolic pathway of lysine to acetyl CoA.

Low levels of essential amino acids may indicate a poor-quality diet, or maldigestion due to deficient digestive peptidase activity or pancreatic dysfunction. 

Lysine intolerance is a rare condition where intestinal absorption and renal tubular reabsorption of lysine, arginine and ornithine are impaired. This results in deficiencies of these amino acids and can lead to hyperammonemia. 

Lastly, vitamin B3 deficiency has been associated with low levels of lysine and other amino acids.

Lysine is a nutritionally essential amino acid abundant in meat, fish, fowl, and legumes and is needed for formation of body proteins and enzymes.

Lysine can be methylated using S-adenosylmethionine (SAM) to synthesize carnitine, which is needed for fatty acid oxidation. Lysine also generates Acetyl CoA for use in the citric acid cycle. Lysine, proline, hydroxyproline, and vitamin C are important in the synthesis of collagen for skin, bones, tendons and cartilage.

L-lysine supplementation has also been studied for herpes simplex treatment and prophylaxis and may be beneficial.