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L-Threonine

Evidence Level
Preliminary
1 Clinical Trial
5 Documented Benefits
1/5 Evidence Score

L-Threonine is an essential amino acid required for collagen and elastin synthesis, immune function, fat metabolism, and central nervous system function. Found in meat, fish, dairy, eggs, lentils, soy. Standalone supplementation is rare — most use is via complete protein or EAA blends. Limited clinical evidence as standalone supplement; some research interest in hereditary spastic paraparesis and other neurological conditions.

Studied Dose Standalone rarely studied; ~7.5 g/day used in hereditary spastic paraparesis trials; RDA: ~20 mg/kg body weight
Active Compound L-Threonine (free amino acid)

Benefits

Collagen and Elastin Synthesis

L-Threonine is a building block for collagen (along with glycine, proline, hydroxyproline) and elastin. Important for skin, connective tissue, joint, and tendon health. Whole-protein collagen sources are more efficient than isolated threonine for these effects.

Supported by Trial 1

Mucin / Gut Mucosal Layer

L-Threonine is a major component of mucin glycoproteins — the protective mucosal layer lining the GI tract. Animal studies suggest threonine is rate-limiting for mucin synthesis; clinical relevance to humans not established.

Supported by Trial 1

Immune Function

L-Threonine contributes to immunoglobulin synthesis. Deficiency impairs antibody production; rare in protein-adequate diets.

Supported by Trial 1

Hereditary Spastic Paraparesis (Limited)

Older small trials examined L-threonine for hereditary spastic paraparesis with mixed signals. Mechanism proposed via glycine pathway. Not standard care; modern HSP management remains primarily supportive.

Supported by Trial 1

ALS Adjunct (Investigational)

Theoretical glycine receptor modulation has prompted exploratory use in amyotrophic lateral sclerosis. Evidence remains preliminary.

Mechanism of action

1

Protein Synthesis

Essential amino acid required for ribosomal protein synthesis. Hydroxyl side chain provides O-glycosylation sites in mucins and other glycoproteins.

2

Glycine Pathway

L-Threonine can be metabolized to glycine via threonine dehydrogenase + serine hydroxymethyltransferase. Theoretical basis for some neurological applications via inhibitory glycine receptors.

3

Mucin Synthesis

Threonine is heavily represented in mucin protein backbones (alongside serine and proline) — the heavily-glycosylated proteins forming the protective mucosal layer in the GI tract and respiratory tract.

4

Lipotropic Effects

Threonine prevents fat accumulation in the liver — works alongside choline, methionine, and inositol as a lipotropic factor. Animal studies more robust than human evidence.

Clinical trials

1
L-Threonine for Hereditary Spastic Paraparesis — Older Trial

Small clinical trial of L-threonine supplementation (7.5 g/day) in patients with hereditary spastic paraparesis. (Neurology — or similar)

Small HSP patient group.

Modest signals on spasticity in some patients; not consistently replicated. Older trial; not standard care. Modern HSP management primarily supportive (PT, baclofen, tizanidine).

Side effects and drug interactions

Common Potential side effects

Generally well-tolerated.
GI distress (nausea, soft stools) at high doses.
Headache reported rarely.

Important Drug interactions

MAOIs — minimal direct interaction; theoretical via amino acid metabolism.
Anticonvulsants — theoretical interaction via glycine pathway; not clinically established.

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Frequently asked questions about L-Threonine

What is L-threonine used for?

L-threonine is an essential amino acid important for collagen and elastin (connective tissue), immune function, and the protective mucus lining of the gut. It is also involved in fat metabolism in the liver.

What is L-threonine good for?

It supports connective tissue, the gut mucosal lining, and immune antibodies, and is sometimes studied for nervous-system support. It is usually obtained from protein rather than supplemented alone.

How much L-threonine should I take?

It is typically consumed through dietary protein; supplemental amounts, when used, follow product labeling. A balanced protein intake supplies adequate threonine for most people.

Is L-threonine safe?

As an essential amino acid from normal protein intake it is generally safe and well tolerated. High-dose isolated supplementation is rarely needed. Those with medical conditions should check with a doctor.

What is L-Threonine?

L-Threonine is an essential amino acid required for collagen and elastin synthesis, immune function, fat metabolism, and central nervous system function. Found in meat, fish, dairy, eggs, lentils, soy. Standalone supplementation is rare — most use is via complete protein or EAA blends.

What is the recommended dosage of L-Threonine?

The clinically studied dose is Standalone rarely studied; ~7.5 g/day used in hereditary spastic paraparesis trials; RDA: ~20 mg/kg body weight Always follow the product label and check with a healthcare provider for personal advice.

Is L-Threonine safe, and does it have side effects?

For most healthy adults, L-Threonine is well tolerated at studied doses. Reported effects can include: Generally well-tolerated. GI distress (nausea, soft stools) at high doses. It may also interact with some medications. L-Threonine is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does L-Threonine interact with any medications?

Possible interactions include: MAOIs — minimal direct interaction; theoretical via amino acid metabolism. Anticonvulsants — theoretical interaction via glycine pathway; not clinically established. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for L-Threonine?

NutraSmarts rates the evidence for L-Threonine as Preliminary (1 out of 5). It is backed by 1 clinical trial and 4 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(4 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Szwiega S, Pencharz PB, Ball RO, Xu L, Kong D, Elango R, Courtney-Martin G Length of Adaptation Has No Effect on the Threonine Requirement Determined in Healthy Young Adult Males Using the Indicator Amino Acid Oxidation Method The Journal of Nutrition. 2023;153(7):2016-2026. doi:10.1016/j.tjnut.2023.03.033.PubMedUsed to support: Human study establishing L-threonine requirement (~10–12 mg/kg/day) in healthy adult males using indicator amino acid oxidation; foundational basis for L-threonine as an essential amino acid with a defined human requirement, relevant to all benefits dependent on adequate threonine status.
  2. Wang C, Yang Y, Gao N, Lan J, Dou X, Li J, Shan A L-Threonine upregulates the expression of β-defensins by activating the NF-κB signaling pathway and suppressing SIRT1 expression in porcine intestinal epithelial cells Food & Function. 2021;12(13):5821-5836. doi:10.1039/d1fo00269d.PubMedUsed to support: Mechanistic cell-biology study (porcine intestinal epithelial cells) showing L-threonine upregulates β-defensin expression and mucosal barrier function via NF-κB signaling. Supports the 'Mucin/Gut Mucosal Layer' and 'Immune Function' benefits; animal/in vitro model, not human trial.
  3. Zhang H, Chen Y, Li Y, Zhang T, Ying Z, Su W, Zhang L, Wang T l-Threonine improves intestinal mucin synthesis and immune function of intrauterine growth-retarded weanling piglets Nutrition. 2019;59:182-187. doi:10.1016/j.nut.2018.07.114.PubMedUsed to support: Animal study (piglets) demonstrating that dietary L-threonine supplementation increases intestinal mucin synthesis, strengthens mucosal barrier, and enhances immune markers. Supports 'Collagen and Elastin Synthesis', 'Mucin/Gut Mucosal Layer', and 'Immune Function' benefit claims; evidence is animal-model, not human RCT.
  4. Growdon JH, Nader TM, Schoenfeld J, Wurtman RJ L-threonine in the treatment of spasticity Clinical Neuropharmacology. 1991;14(5):403-12. doi:10.1097/00002826-199110000-00003.PubMedUsed to support: Double-blind crossover clinical trial (n=18 patients with familial spastic paraparesis) of L-threonine at 4.5–6.0 g/day vs placebo; supports the 'Hereditary Spastic Paraparesis' benefit claim. This is the key human clinical reference for neurological use of L-threonine.