Also known as: Lysine, L-lysine HCl, Lysine monohydrochloride
FoundationalGood evidence
An essential amino acid required for collagen cross-linking and carnitine synthesis. The limiting amino acid in grain-based diets, and the one that competes directly with arginine.
Typical dose
1.0–3.0 g per day
Empty stomach; separate from arginine or citrulline
What it is
L-lysine is one of the nine essential amino acids. It is abundant in animal proteins, particularly meat, fish, eggs and dairy, and in legumes, but notably scarce in cereal grains.
This makes lysine the limiting amino acid in grain-based diets, meaning it runs out first and caps how much of the remaining protein can be used. It is the nutritional reason why traditional cuisines pair grains with legumes, from rice and dal to beans and tortillas, since legumes supply the lysine grains lack.
Beyond protein building, lysine is required for the enzymes that cross-link collagen, giving connective tissue its tensile strength, and is a precursor for carnitine synthesis.
How it works
Lysine and arginine compete for the same intestinal and cellular transporters, so raising intake of one shifts the balance against the other. This competition is the basis for most of what lysine is used for outside straightforward protein nutrition.
In connective tissue, lysine residues are hydroxylated and then cross-linked by lysyl oxidase, a step that converts newly formed collagen into a mechanically strong structure. This process is vitamin C dependent, which is why the two are often discussed together.
Lysine also improves intestinal calcium absorption and reduces its urinary excretion, which underpins interest in it for bone health, though this is a secondary consideration.
What the evidence shows
Evidence in populations with genuinely low intake, particularly grain-dependent diets, is reasonably strong for growth and protein status. In well-fed omnivores consuming adequate protein, shortfall is essentially absent.
Research on calcium absorption and bone markers is modest but consistent in direction, fitting the mechanism rather than proving an outcome.
Claims relating to stress and mood rest on a small number of studies conducted largely in populations with low dietary lysine, and should not be generalised to someone already eating plenty of protein.
Dosing
Common supplemental range is 1-3 g daily.
For general use in a diet low in animal protein or legumes, 1 g daily is a reasonable addition. Most people eating adequate protein will not need it at all.
Take on an empty stomach for better absorption, and away from arginine or citrulline supplements, since the two compete directly for the same transporters. If you are taking lysine alongside a pre-workout containing citrulline, separate them by several hours or they will work against each other.
At a glance
Common forms
L-lysine HCl capsules, L-lysine powder, Topical lysine creams, Within EAA blends
Half-life / duration
Plasma lysine peaks within 1-2 hours
Timing
Empty stomach; separate from arginine or citrulline
Competition status
Permitted — not on the WADA Prohibited List
Category
Foundational
Safety and side effects
Lysine is well tolerated. It is an ordinary dietary component and doses up to several grams daily have been used in trials without significant adverse effects. Digestive upset, cramping and diarrhoea are occasionally reported at higher intakes.
Because lysine increases calcium absorption, take care if you already take calcium in high doses.
There have been isolated reports of concerns with very high long-term intakes, so anyone who has been told their kidneys are not working normally should seek advice, as should anyone taking regular medication.
Who should avoid it
Speak to your doctor before use if you have been told your kidneys are not working normally, or if you take regular medication. Take care alongside high-dose calcium. Not established for use in pregnancy or breastfeeding at supplemental doses.
This entry is provided for information only. Food supplements should not be used as a substitute for a varied and balanced diet and a healthy lifestyle. Consult a qualified healthcare professional before use if you are pregnant, breastfeeding, taking medication or under medical supervision.
