What Is L-Lysine and How Does It Work?
L-lysine is an essential amino acid β meaning the body cannot synthesise it and must obtain it through diet or supplementation. It is found in protein-rich foods such as meat, fish, eggs, and dairy. As a supplement, L-lysine is taken for a range of proposed benefits including support for collagen formation, immune function, and prevention of cold sore recurrence (oral herpes caused by HSV-1).
The biological roles of lysine are well established: it is a structural component of collagen (required to form hydroxylysine residues that cross-link collagen fibres), a precursor to carnitine (which plays a role in fatty acid metabolism), and it competes with arginine for cellular uptake β the basis of its proposed antiviral mechanism.
Products available at maxfit.ee in this category include NOW L-Lysine 1000mg 100tabs and OstroVit Lysine 200g β both straightforward single-amino acid supplements.
What the Evidence Shows
Collagen Synthesis
Lysine is an established, physiologically necessary component of collagen. Hydroxylysine residues are critical to the structural stability of collagen fibres. This is a well-described biochemical function, not a therapeutic claim β it reflects normal physiology. Lysine deficiency is associated with impaired wound healing and collagen integrity.
EFSA has approved the claim that lysine contributes to normal growth in the context of adequate dietary protein β a reflection of its essential amino acid status.
Herpes Simplex Prevention
The evidence for lysine supplementation in reducing HSV-1 cold sore frequency is the most discussed clinical application. The rationale is that HSV replication requires arginine, and lysine competes with arginine for intestinal absorption and cellular uptake, potentially suppressing viral replication. Several small clinical trials have reported reduced recurrence frequency and severity with lysine supplementation.
A systematic review by Mailoo & Rampes (2017) examined the available trials and concluded that the evidence was suggestive but limited by small sample sizes and methodological variability. No large, adequately powered, high-quality RCT exists. The effect, if real, appears to be dose-dependent and more consistent at higher intake levels.
Athletic Performance and Muscle
As an essential amino acid, adequate lysine intake is necessary for muscle protein synthesis (along with all other essential amino acids). There is no specific evidence that lysine supplementation beyond dietary sufficiency enhances muscle growth or athletic performance in healthy individuals consuming adequate protein.
Effect Sizes and Who May Benefit
For individuals who are lysine-sufficient from diet (most omnivores), supplemental lysine is unlikely to produce measurable benefits for collagen synthesis or muscle. Potential beneficiaries include:
- People with frequent cold sore recurrences looking for a low-risk adjunct approach
- People on restrictive low-protein diets at risk of lysine deficiency (some vegan diets emphasise grains, which are low in lysine)
- Individuals recovering from burns or wounds where collagen turnover is high
EFSA-Approved Claims
EFSA has approved the health claim that lysine (as part of dietary protein) "contributes to the growth and maintenance of muscle mass" and "contributes to the maintenance of normal bones" within the broader context of protein nutrition. These are protein-class claims that apply to complete essential amino acid provision, not specifically to lysine supplementation in isolation.
Safety
L-lysine is generally well tolerated at typical supplemental doses. At very high doses, gastrointestinal side effects (nausea, abdominal cramps, diarrhoea) have been reported. There are theoretical interactions with aminoglycosidic antibiotics (elevated lysine may compete for renal reabsorption, potentially affecting kidney exposure to the drug), but this is not a well-established clinical concern at typical supplement doses.
Honest Verdict
L-lysine is an essential nutrient with clear physiological importance. The evidence for specific therapeutic benefits from supplementation β beyond correcting deficiency β is modest and application-specific. The most supported use is in reducing cold sore recurrence in people prone to HSV-1 outbreaks, though the evidence base remains limited. Lysine is safe, inexpensive, and low-risk, making it a reasonable option for specific use cases.
References
Griffith, R. S., Walsh, D. E., Myrmel, K. H., Thompson, R. W., & Behforooz, A. (1987). Success of L-lysine therapy in frequently recurrent herpes simplex infection. Dermatologica, 175(4), 183-190. https://pubmed.ncbi.nlm.nih.gov/3115841/
Civitelli, R., Villareal, D. T., Agnusdei, D., Nardi, P., Avioli, L. V., & Gennari, C. (1992). Dietary L-lysine and calcium metabolism in humans. Nutrition, 8(6), 400-405. https://pubmed.ncbi.nlm.nih.gov/1486246/
Does L-lysine help prevent cold sores?
Some small clinical trials suggest L-lysine supplementation may reduce cold sore recurrence frequency in people prone to HSV-1 outbreaks. The evidence is suggestive but limited β no large, high-quality RCT exists. It is low-risk to try as an adjunct approach.
Who is most likely to be deficient in lysine?
People following grain-heavy vegan diets may have lower lysine intake, as most grains are relatively low in lysine. Omnivores consuming adequate protein from meat, eggs, or dairy are unlikely to be deficient.
Where can I find L-lysine supplements in Estonia?
You can browse lysine options at maxfit.ee in the individual amino acids section.
