An essential amino acid concentrated in the mucus lining of the gut and in collagen and elastin. Important physiologically, but with almost no case for isolated supplementation in a well-fed person.
Typical dose
500.0–2000.0 mg per day
With food, if used
What it is
L-threonine is one of the nine essential amino acids. It is found in meat, fish, dairy, eggs, lentils and, in reasonable amounts, in many plant proteins. It was the last essential amino acid to be identified, in the 1930s.
Its most distinctive role is in mucin, the glycoprotein that forms the protective mucus layer lining the digestive tract. Mucins are unusually rich in threonine, which means gut mucus production consumes a substantial share of dietary threonine.
It is also a significant component of collagen and elastin, and can be converted to glycine and serine. It is one of the amino acids most commonly added to animal feed, where threonine limitation is a real production issue, which is a considerably more relevant application than human supplementation.
How it works
Threonine residues in mucin proteins carry the attached sugar chains that give mucus its gel-like protective properties. Adequate threonine is therefore necessary for maintaining the intestinal mucus barrier.
Its hydroxyl side chain is also a site for phosphorylation, one of the main ways cells switch protein activity on and off, making threonine residues important in cell signalling generally.
Threonine can be metabolised to glycine and then serine, contributing to the pool used for collagen, glutathione and creatine synthesis. It also feeds into the production of the neurotransmitter glycine in the central nervous system.
What the evidence shows
There is essentially no evidence supporting isolated threonine supplementation in healthy people with adequate protein intake, and no established performance or body composition benefit.
Most of the meaningful research is in animal nutrition, where threonine limitation demonstrably affects gut integrity and growth. Human work on gut barrier function is largely mechanistic rather than interventional.
Older supervised research explored threonine in a small number of specialist medical contexts, based on its relationship to glycine, with modest findings. Those settings are not a reason for general supplementation.
Dosing
Supplemental doses of 500 mg to 2 g daily appear in products, but there is no established protocol because there is no clearly established purpose.
Ordinary protein intake supplies threonine comfortably. A 25 g serving of whey delivers well over a gram, and an omnivorous diet supplies several grams daily.
If gut barrier support is the goal, glutamine has a considerably better-developed literature. If the aim is a complete amino acid profile, an EAA product or simply adequate protein covers threonine without needing to think about it.
At a glance
Common forms
L-threonine powder, Capsules, Within EAA blends
Half-life / duration
Plasma threonine peaks within 1-2 hours
Timing
With food, if used
Competition status
Permitted — not on the WADA Prohibited List
Category
Foundational
Safety and side effects
Threonine is well tolerated. It is an ordinary dietary component and supplemental doses have not been associated with significant adverse effects, with mild digestive upset the occasional complaint.
Older studies used doses considerably higher than typical supplement servings without notable safety problems.
As with all amino acids, anyone under medical care or taking regular medication should check before use. Long-term data on isolated supplementation is limited.
Who should avoid it
Speak to your doctor before use if you take regular medication or are under medical care. Not established for use in pregnancy or breastfeeding at supplemental doses. No significant interactions established.
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.
