L-Threonine

botanicalL-threonine

What is it

L-threonine is an essential amino acid that the body cannot synthesize and must obtain from food. It supports protein synthesis, immune function, intestinal mucus production, and connective tissue and tooth enamel structure.

How it works

L-threonine is absorbed in the small intestine and used in protein synthesis throughout the body. It is particularly abundant in mucin proteins that line the gut, where it helps maintain the protective mucus layer of the intestinal wall. Threonine is also a key component of immune system proteins, particularly antibodies, supporting humoral immunity. In metabolism, threonine can be converted to glycine and acetyl-CoA via the threonine dehydrogenase pathway, contributing to energy production and one-carbon metabolism. Its hydroxyl group makes threonine a target for protein phosphorylation, an important regulatory mechanism in cell signaling. Threonine is also notable for its role in collagen and elastin synthesis, supporting connective tissue health, and is incorporated into tooth enamel proteins. Severe deficiency causes growth impairment, immune dysfunction, and gastrointestinal problems.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Threonine deficiency / nutritional repletion

Grade A

Strong evidence

Supplementation reverses deficiency in restricted diets, parenteral nutrition, and certain inflammatory conditions. As an essential amino acid, adequate intake is required for growth, immunity, and protein synthesis.

Spasticity (multiple sclerosis, spinal cord injury)

Grade C

Moderate evidence

Some older studies used high-dose L-threonine (4.5-7.5 g/day) for spasticity in MS and ALS with mixed results, possibly through effects on glycine metabolism and inhibitory neurotransmission. Not a standard treatment.

Gut barrier / mucin production

Grade C

Moderate evidence

Threonine is highly enriched in intestinal mucins. Animal and limited human evidence suggests adequate threonine supports gut barrier integrity, particularly in stressed or inflammatory states. Direct supplementation evidence in humans is limited.

Immune function (antibody synthesis)

Grade C

Moderate evidence

Threonine is essential for immunoglobulin synthesis. Deficiency impairs humoral immunity. Whether supplementation in non-deficient adults boosts immunity is not well-established.

Wound healing / connective tissue

Grade D

Mixed evidence

Threonine contributes to collagen and elastin synthesis. Direct evidence that supplementation accelerates wound healing in humans is limited.

1 commercial form

L-threonine (free form)

Standard supplement form; well absorbed.

The natural isomer used in proteins.

Dosage

The RDA for threonine is 20 mg/kg/day (about 1,400 mg for a 70 kg adult). Supplement doses typically range 500-2,000 mg/day. Some studies in spasticity have used 4.5-6 g/day. No formal UL exists; doses up to several grams per day appear well-tolerated.

When and how to take it

L-threonine can be taken with or without food. Empty stomach dosing may improve absorption. Split larger doses across the day for steady amino acid availability. Most users tolerate morning dosing well; no strict preferred time.

Food sources

Food	Amount	%DV
Chicken breast (3 oz, cooked)	1,200 mg	—
Beef (3 oz, cooked)	1,100 mg	—
Tuna (3 oz, cooked)	1,100 mg	—
Salmon (3 oz, cooked)	950 mg	—
Eggs (1 large)	300 mg	—
Cottage cheese (1/2 cup)	560 mg	—
Lentils (1 cup, cooked)	660 mg	—
Soybeans (1 cup, cooked)	1,200 mg	—

Safety

L-threonine at typical supplement doses is well-tolerated. Higher doses may cause GI upset, headache, or skin rash in sensitive individuals. Long-term safety at very high doses is not well-characterized. Avoid in inherited threonine metabolism disorders.

Who should be cautious

Pregnant and lactating women should not exceed dietary amounts unless directed by a clinician. Children should not take high-dose supplements without medical guidance. Caution in liver or kidney disease. People with hereditary disorders affecting threonine metabolism should not supplement.

Interactions

Few significant drug interactions documented. May modestly compete with other amino acids for transport at high doses. May enhance the breakdown of other amino acids if very high doses are consumed without adequate complete protein.

Frequently asked questions

Do I need a threonine supplement?⌄

Probably not. Most omnivorous diets provide ample threonine. Supplementation may be considered for specific clinical situations like inflammatory bowel disease, malnutrition, or research protocols.

Does threonine help my gut?⌄

Threonine is concentrated in intestinal mucin proteins, which form the protective gut barrier. Adequate intake supports gut integrity, but supplementation in healthy adults has limited direct evidence.

Can threonine help with spasticity?⌄

Older studies of high-dose threonine for spasticity in MS or ALS showed mixed results. It is not part of standard care.

Is threonine safe?⌄

Yes, at dietary and typical supplement doses. Long-term high-dose safety is less well-characterized.

What foods are high in threonine?⌄

Animal proteins (meat, fish, poultry, dairy, eggs), legumes (lentils, soybeans), and certain seeds. Vegetarians and vegans can get enough from varied plant proteins.

References

L-Threonine - Wikidata — Wikidata link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.