Vitamin B1 (Thiamine)

1. Introduction

Vitamin B1, also known as Thiamine, is one of the eight water-soluble B-complex vitamins. As an essential micronutrient, it cannot be synthesized by the human body and must be obtained through diet or supplementation [1, 2]. Thiamine is naturally present in foods such as whole grains, pork, poultry, nuts, and dried beans, and is also added to fortified grain products [1].

Chemical/Botanical Basics

Thiamine is a compound composed of a pyrimidine ring and a thiazole ring connected by a methylene bridge [2]. It is the first vitamin to be chemically identified, hence its designation as B1. In the body, thiamine exists in various phosphorylated forms, including thiamine monophosphate (TMP), thiamine triphosphate (TTP), and its most biologically active form, Thiamine Pyrophosphate (TPP), also known as cocarboxylase [2].

Mechanism of Action

The primary function of thiamine is its role as the essential cofactor, Thiamine Pyrophosphate (TPP), for several key enzymes involved in energy metabolism [1, 2]. These enzymes include:

1. Pyruvate Dehydrogenase (PDH): Catalyzes the conversion of pyruvate to acetyl-CoA, linking glycolysis to the citric acid (Krebs) cycle.
2. α-Ketoglutarate Dehydrogenase (α-KGDH): A key enzyme in the Krebs cycle.
3. Transketolase: A critical enzyme in the pentose phosphate pathway, which is essential for the synthesis of NADPH and the ribose sugars needed for DNA and RNA synthesis [2].

By facilitating these metabolic processes, thiamine is crucial for carbohydrate, lipid, and branched-chain amino acid metabolism, playing a vital role in energy production, especially in the brain and nervous system [1, 2].

2. Chemical Composition/Key Bioactive Roles

Thiamine’s biological activity is primarily mediated by its phosphorylated derivatives, with TPP being the most significant.

Compound Name	Chemical Role	Biological Function
Thiamine (Vitamin B1)	Free form (dietary)	Precursor to active cofactors
Thiamine Pyrophosphate (TPP)	Coenzyme (Cocarboxylase)	Cofactor for key metabolic enzymes (PDH, α-KGDH, Transketolase) in carbohydrate metabolism and energy production [1, 2].
Thiamine Triphosphate (TTP)	Signaling molecule	May play a role in neuronal membrane function and nerve impulse transmission [2].

3. Health Benefits

Thiamine is essential for maintaining cellular health and energy metabolism, with its deficiency leading to severe neurological and cardiovascular disorders [1, 2].

Preventing Thiamine Deficiency Disorders

Wernicke-Korsakoff Syndrome (WKS): WKS is a severe neurological disorder resulting from chronic thiamine deficiency, most commonly associated with alcohol use disorder [1]. It presents in two phases:

• Wernicke Encephalopathy (WE): Characterized by a triad of symptoms: ophthalmoplegia (eye movement abnormalities), ataxia (impaired coordination), and confusion [1].
• Korsakoff Psychosis: A chronic, debilitating memory disorder characterized by severe short-term amnesia and confabulation [1].
  Thiamine is FDA-approved for the treatment of WE, with high-dose parenteral administration being the standard of care [1].

Beriberi: A disorder caused by thiamine deficiency, presenting in two forms [1]:

• Wet Beriberi: Primarily affects the cardiovascular system, leading to high-output cardiac failure, edema, and respiratory distress [1].
• Dry Beriberi: Affects the nervous system, causing peripheral neuropathy, muscle weakness, and, in severe cases, paralysis [1].
  Thiamine supplementation is the definitive treatment for both forms of beriberi [1].

Supporting Nervous System Function

Thiamine is critical for the proper functioning of the central and peripheral nervous systems [2]. Its role in glucose metabolism ensures the high energy demands of neurons are met. Furthermore, TPP is involved in the synthesis of neurotransmitters, and TTP may play a direct role in nerve impulse transmission [2].

Potential Role in Cognitive Health

Thiamine deficiency is implicated in several neurodegenerative diseases, including Alzheimer’s and Parkinson’s disease, suggesting its importance for long-term cognitive health [2]. Supplementation has been studied for its potential to improve cognitive function, particularly in individuals with subclinical deficiencies.

4. Dosage and Usage

Recommended Daily Allowance (RDA)

The recommended daily intake of thiamine varies by age and sex. For most healthy adults, the RDA is [3]:

Group	RDA (mg/day)
Adult Men (19+ years)	1.2 mg
Adult Women (19+ years)	1.1 mg
Pregnant/Lactating Women	1.4 mg

Food Sources

Thiamine is widely available in the diet. Rich sources include [1]:

• Whole grains and fortified cereals
• Pork and other meats
• Dried beans, peas, and nuts
• Soybeans

Therapeutic Dosage

For the treatment of severe thiamine deficiency (e.g., Wernicke Encephalopathy), high-dose parenteral (IV or IM) administration is used. Typical therapeutic dosages are:

• Treatment of Wernicke Encephalopathy: 100 mg IV/IM per day for 3 to 5 days, or until the patient is able to maintain a normal dietary intake [1]. Some protocols recommend higher doses (e.g., 200-500 mg) [3].
• General Supplementation: Multivitamins commonly contain about 1.5 mg of thiamine, which is sufficient for healthy individuals [1].

5. Safety and Precautions

Thiamine is a water-soluble vitamin, and any excess is rapidly excreted in the urine, making it exceptionally safe [2, 3]. No Upper Limit (UL) has been established for thiamine intake due to the lack of reported toxicity from oral administration [3].

Side Effects

• Oral Supplementation: Side effects are extremely rare with oral intake [3].
• Parenteral Administration: Rapid intravenous injection may rarely cause mild side effects such as nausea, restlessness, or transient vasodilation [3].

Contraindications

• There are no absolute contraindications to thiamine use, except for a documented hypersensitivity or allergy to thiamine, which is rare [1].

Drug Interactions

• Diuretics (e.g., Furosemide): Long-term use of loop diuretics can increase thiamine excretion, potentially leading to deficiency, especially in older adults [3].
• Alcohol: Chronic alcohol consumption interferes with thiamine absorption, storage, and phosphorylation to its active form, TPP, which is the primary cause of Wernicke-Korsakoff syndrome in this population [1].

Warnings

SERIOUS WARNING: Thiamine is critical for individuals at risk of deficiency.
In patients with marginal thiamine status (e.g., those with alcohol use disorder, malnutrition, or persistent vomiting), administering intravenous dextrose (glucose) without prior or concurrent thiamine can precipitate or worsen Wernicke Encephalopathy [1]. This is because the metabolism of glucose requires thiamine (as TPP), rapidly depleting the already low reserves [1]. Therefore, thiamine should always be administered before or with dextrose in at-risk patients [1].

6. References

[1] Martel, J. L., Doshi, H., Sina, R. E., & Franklin, D. S. (2024). Vitamin B1 (Thiamine). StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from: [https://www.ncbi.nlm.nih.gov/books/NBK482360/]()[2] Mrowicka, M., Mrowicki, J., Dragan, G., & Majsterek, I. (2023). The importance of thiamine (vitamin B1) in humans. Bioscience Reports, 43(10), BSR20230374. doi: [10.1042/BSR20230374](). Available from: [https://pmc.ncbi.nlm.nih.gov/articles/PMC10568373/]()[3] National Institutes of Health (NIH) Office of Dietary Supplements (ODS). (2024). Thiamin Fact Sheet for Health Professionals. Available from: https://ods.od.nih.gov/factsheets/Thiamin-HealthProfessional/