Lysine is one of the nine essential amino acids. This classification indicates that these amino acids are essential for life, cannot be manufactured by the human body, and must be obtained from food.

Amino acids form the structure for all proteins. Lysine plays many roles in human metabolism, and one of lysine’s most crucial functions is its metabolism into acetyl coenzyme A, one of the key components in the Krebs cycle. 


Background


In the four decades after it was first identified in 1889,1 lysine’s chemical structure was mapped, and it was successfully synthesized in the laboratory. In addition to its role in the Krebs cycle, lysine has many other functions within human metabolism, including aiding in the conversion of fats into energy, improving calcium absorption by bone, forming a matrix for collagen, and helping maintain the serotonergic pathway in the brain. 


In alternative medicine, lysine supplementation has been most discussed as a potential treatment for outbreaks of herpes simplex virus (HSV) infection. Lysine deficiency is relatively uncommon in the United States, but strict vegans can be at risk, as the main source of lysine is animal protein. 


Science


The proposed mechanism by which lysine affects the HSV (primarily HSV type 1 or herpes labialis) is by interfering with the metabolic balance of lysine and arginine.2 HSV cells synthesize higher levels of arginine and lower levels of lysine than human host cells. Increasing cellular lysine concentrations disrupts HSV’s balance between lysine and arginine and inhibits viral replication. 


Research on lysine for early resolution of lesions or prevention of outbreaks has shown some marginal, albeit not statistically significant, improvement. One trial treated 65 patients with histories of recurrent herpes labialis with 1,000 mg of lysine daily for 12 weeks, after which the patients shifted to placebo treatment for 12 weeks.3

Overall, lysine supplementation did not improve healing of active lesions or better prevent the recurrence of outbreaks. However, patients were more likely to be either recurrence-free or have fewer outbreaks on lysine. A small five-month trial of 21 patients with histories of recurrent and frequent outbreaks of HSV found that lysine was no more effective than placebo in these patients.4

Another potential use of lysine supplementation is in the treatment of depression and anxiety. It is thought that lysine deficiency results in a pathological increase in serotonin in the amygdala, which is responsible for emotional regulation and stress response.5 When serotonin increases unchecked, the amygdala becomes overstimulated, resulting in a low-level serotonin syndrome with anxiety, diarrhea, and other symptoms of excess serotonin. 


One study looked at the effect of eating lysine-enriched foods on anxiety in 93 households in an area known to have a low intake of lysine-rich foods.6 At baseline and at the end of the three-month trial, subjects were screened using the State-Trait Anxiety Inventory. In participants with relatively high pre-study anxiety scores, post-study scores after lysine supplementation decreased the most, with an average change of 6.9 points.

Although this is a small difference, it corresponds well with known anxiolytic pharmaceuticals including fluoxetine (8.1-point reduction) and diazepam (6.8-point reduction).6