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What is Vitamin B1 (Thiamin) and What is the symptoms of Vitamin B1 Deficiency and Toxicity ?

Thiamin (thiamine), or vitamin B1, is a water-soluble vitamin found naturally in some foods, added to foods, and sold as a supplement. Thiamin plays a vital role in the growth and function of various cells.  Only small amounts are stored in the liver, so a daily intake of Thiamin-rich foods is needed.

Food sources of thiamine include whole grains, legumes, and some meats and fish.  Grain processing removes much of the thiamine content, so in many countries cereals and flours are enriched with thiamine.   Supplements and medications are available to treat and prevent thiamine deficiency and disorders that result from it, including beriberi and Wernicke encephalopathy.

Other uses include the treatment of maple syrup urine disease and Leigh syndrome.  They are typically taken by mouth, but may also be given by intravenous or intramuscular injection.

Thiamine supplements are generally well tolerated. Allergic reactions, including anaphylaxis, may occur when repeated doses are given by injection. Thiamine is in the B complex family. It is an essential micronutrient, which cannot be made in the body. Thiamine is required for metabolism including that of glucose, amino acids, and lipids.

Thiamine was discovered in 1897, was the first vitamin to be isolated in 1926, and was first made in 1936. It is on the World Health Organization’s List of Essential Medicines, the safest and most effective medicines needed in a health system. Thiamine is available as a generic medication, and as an over-the-counter drug.

Although symptoms of thiamin deficiency were first recorded in ancient texts of Chinese medicine, the symptoms were not connected with diet until the late 19th century. In 1884, a Japanese physician noted very high rates of illness and death among Japanese sailors eating a limited diet of only rice for months while at sea. When given a more varied diet with whole grains, meats, beans, and vegetables, rates of illness and death nearly disappeared. Around the same time, two Dutch scientists observed that chickens fed white polished rice developed leg paralysis, whereas chickens fed brown unpolished rice did not. Their observations led to the discovery of thiamin present in the outer layers of rice that were removed with polishing.

Recommended Vitamin B Intakes

Intake recommendations for thiamin and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences). DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and sex, include:

  • Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
  • Adequate Intake (AI): Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.
  • Estimated Average Requirement (EAR): Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.
  • Tolerable Upper Intake Level (UL): Maximum daily intake unlikely to cause adverse health effects.

Table 1 lists the current RDAs for thiamin . For infants from birth to 12 months, the FNB established an AI for thiamin that is equivalent to the mean intake of thiamin in healthy, breastfed infants.

Table 1: Recommended Dietary Allowances (RDAs) for Thiamin 【1】
Age Male Female Pregnancy Lactation
Birth to 6 months* 0.2 mg 0.2 mg
7–12 months* 0.3 mg 0.3 mg
1–3 years 0.5 mg 0.5 mg
4–8 years 0.6 mg 0.6 mg
9–13 years 0.9 mg 0.9 mg
14–18 years 1.2 mg 1.0 mg 1.4 mg 1.4 mg
19-50 years 1.2 mg 1.1 mg 1.4 mg 1.4 mg
51+ years 1.2 mg 1.1 mg



Vitamin B1 and Health

Because thiamin is involved in several basic cell functions and the breakdown of nutrients for energy, a deficiency can lead to various problems in the brain and heart that require a constant supply of energy.   

Congestive heart failure

A deficiency of thiamin can lead to abnormal motor functions in the heart. Congestive heart failure is a condition that prevents the heart from properly pumping blood to the rest of the body. The rate of thiamine deficiency in people with congestive heart failure ranges from 21%-98%. [1] It occurs particularly in the elderly, those with a poor nutritional intake, or with the use of high doses of diuretics. Some clinical trials have found that thiamin supplementation compared with a placebo can significantly improve heart function in people with heart failure. [2]

Cognitive function

Research has shown that thiamin deficiency can lead to neurological problems such as cognitive decline. [3] One form of thiamin deficiency called Wernicke-Korsakoff syndrome exhibits mental status changes similar to Alzheimer’s disease. Animal studies suggest that a lack of thiamin may cause oxidative stress or the death of nerve cells, memory loss, formation of plaque, and reduced glucose metabolism, which are all risk factors for Alzheimer’s disease. Research in humans has been limited, so it is not yet clear if thiamin supplementation can help this condition.

Wernicke-Korsakoff syndrome

Wernicke-Korsakoff syndrome is one of the most severe neuropsychiatric sequelae of alcohol abuse. The authors of a 2013 Cochrane review of thiamin to treat or prevent Wernicke-Korsakoff syndrome found only two studies that met their inclusion criteria, and one of these studies has not been published . These randomized, double-blind, placebo-controlled trials compared 5 mg/day by mouth for 2 weeks or daily intramuscular doses of 5 to 200 mg/day thiamin over 2 consecutive days in a total of 177 people with a history of chronic alcohol use. The Cochrane review authors concluded that the evidence from randomized clinical trials is insufficient to guide healthcare providers in selecting the appropriate dose, frequency, duration, or route of thiamin supplementation to treat or prevent Wernicke-Korsakoff syndrome in patients with alcohol abuse.

The authors of the European Federation of Neurological Societies guidelines for diagnosing, preventing, and treating Wernicke’s encephalopathy note that even high doses of oral thiamin supplements might not be effective in raising blood thiamin levels or curing Wernicke’s encephalopathy. They recommend 200 mg thiamin, preferably intravenously, three times daily (total of 600 mg/day) until the signs and symptoms stop, along with a balanced diet. In its guidelines for managing Wernicke’s encephalopathy in emergency departments, the Royal College of Physicians in London supports the administration of oral thiamin hydrochloride (100 mg three times a day) in patients with adequate dietary intakes of thiamin and no signs or symptoms of Wernicke’s encephalopathy. However, the authors recommend parenteral thiamin supplementation for patients at high risk, such as those with ataxia, confusion, and a history of chronic alcohol misuse, because oral supplementation is unlikely to produce adequate blood levels.


The proportion of people with type 1 or type 2 diabetes who have poor thiamin status based on erythrocyte transketolase activity ranges from 17% to 79% in studies conducted to date. In a study of 76 consecutive patients with type 1 or type 2 diabetes, for example, 8% had mild thiamin deficiency and 32% had moderate deficiency based on assays of the transketolase enzyme .

Some small studies have shown that oral supplementation with 150–300 mg/day thiamin can decrease glucose levels in patients with type 2 diabetes or impaired glucose tolerance. However, the authors of these studies did not assess the potential clinical significance of these findings.

A few small randomized studies have assessed the effects of benfotiamine supplements on diabetic neuropathy. Three studies found that, compared to placebo, 120–900 mg/day benfotiamine with or without other B-vitamins decreased the severity of neuropathy symptoms and lowered urinary albumin excretion (a marker of early-stage diabetic nephropathy) . However, another study found no effect of 900 mg/day benfotiamine on urinary excretion of albumin or kidney injury molecule-1, a marker of kidney injury.

Well-designed studies with larger sample sizes and longer durations are required to determine whether thiamin supplements can reduce glucose levels in patients with diabetes or decrease diabetic complications.

Heart failure

The rates of poor thiamin status in patients with heart failure have ranged in studies from 21% to 98%. Explanations for this association include older age, comorbidities, insufficient dietary intake, treatment with diuretics, and frequent hospitalizations .

The authors of one study reported that 33% of 100 patients with chronic heart failure had thiamin deficiency compared to 12% of 50 healthy volunteers . Rates of deficiency were even higher when the investigators excluded those who used thiamin supplements. The different rates of thiamin deficiency in patients with heart failure in these and other studies are probably due to differences in nutrition status, comorbidities, medications and dietary supplements used, and techniques used to measure thiamin status.

The authors of a systematic literature review and meta-analysis found two randomized, double-blind, placebo-controlled trials of thiamin supplementation in people with heart failure that met their eligibility criteria . In these trials, thiamin supplements significantly improved net change in left ventricular ejection fraction. The authors did not assess the clinical significance of this finding, however.

More research is needed to determine whether thiamin supplements might benefit people with heart failure, even if they have normal thiamin status.

Alzheimer’s disease

According to animal model studies, thiamin deficiency might play a role in the development of Alzheimer’s disease. For example, thiamin deficiency produces oxidative stress in neurons, death of neurons, loss of memory, plaque formation, and changes in glucose metabolism—all markers of Alzheimer’s disease. Autopsy studies have shown that transketolase and other thiamin-dependent enzymes have decreased activity in the brains of people with Alzheimer’s disease.

Few studies have assessed the prevalence of thiamin deficiency in people with Alzheimer’s disease. One of these studies found that 13% of 150 patients with cognitive impairment and acute-onset behavioral disturbances were considered thiamin deficient based on plasma levels .

The authors of a 2001 Cochrane review assessed three double-blind, randomized trials (including two crossover trials) that compared the effects of 3 g/day oral thiamin to placebo on cognitive function in patients with Alzheimer’s type dementia . The three studies randomly assigned fewer than 20 patients each, and the two crossover studies did not include a washout period [57-59]. The review authors stated that it was not possible to draw any conclusions from these three studies because they were small and the publications describing them did not provide enough detail to combine these data in a meta-analysis.

Larger, well-designed studies are needed to determine whether thiamin supplements are beneficial for Alzheimer’s disease.

USANA CellSentials supplement facts

  2. DiNicolantonio JJ, Lavie CJ, Niazi AK, O’Keefe JH, Hu T. Effects of thiamine on cardiac function in patients with systolic heart failure: systematic review and meta-analysis of randomized, double-blind, placebo-controlled trials. Ochsner Journal. 2013 Dec 21;13(4):495-9.
  3. Gibson GE, Hirsch JA, Fonzetti P, Jordon BD, Cirio RT, Elder J. Vitamin B1 (thiamine) and dementia. Annals of the New York Academy of Sciences. 2016 Mar;1367(1):21.

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