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Vitamin B1 (Thiamin)

What is vitamin B1?

Vitamin B1 is usually referred to by its name rather than it’s number, and it goes by the name of thiamin. It is also the first water-soluble vitamin I am covering here on the website(click here to review the difference between fat and water soluble vitamins).

The discovery of “thiamine”

This vitamin was discovered in a very interesting way. Late in the 1800s, a Dutch researcher found that birds fed a diet of nutrient-poor rice that did not have the outer layers containing most of the vitamins, they developed neurological problems. This discovery led to a better understanding of the vitamin we know now as thiamin, and also its deficiency disease, beriberi, which you can read on to learn more about later in this article.

What does the body use thiamin for?

The B1 vitamin is used to help our body in many important functions. It aids in the following activities:

  • Generating energy from nutrients (particularly carbohydrates) -- in other words it is important for the body to produce energy

  • Growth, development, and function at the cellular level

  • Normal appetite and digestive functions

  • Supports nervous system functions

Dietary Reference Intakes (DRIs)

An important aspect of thiamin intake is that around pre-adolescent and adolescent years, the recommendations for males and females begin to differ ever so slightly. When assessing intake with your healthcare team, it is important to be mindful of all the sources you are taking, including supplements.


Remember, since thiamin is a water-soluble vitamin that means what is not being used by the body is excreted. As such, disorders affecting how the body uses thiamin, or disorders that cause higher levels of excretion, can have devastating effects on the body of those dealing with the deficiency.

What are potential causes of deficiency?

  • Poor dietary intake

  • Inadequate parenteral nutrition

  • Reduced gastrointestinal (GI) absorption

  • Increased metabolic requirements

  • Excessive loss of thiamin

  • Chronic alcohol consumption (primary cause of deficiency in industrialized countries)

  • Alterations in glucose metabolism of diabetic patients

  • Alzheimer's disease

  • diuretic -induced excretion

A deficiency of the vitamin B1 (thiamin) can lead to two primary conditions.

Wernicke's encephalopathy is an acute (short-term) neurological disorder that appears secondary to a thiamin deficiency. Wernicke-Korsakoff's syndrome is a neurological condition that develops when there are persistent alterations in memory formation accompanying encephalopathy.

Beriberi is a condition involving nerve damage in both the peripheral and central nervous systems, but it can affect multiple organ systems. In general, it causes nervous system and cardiac dysfunction. There are two main types of beriberi, wet and dry. Dry beriberi results from chronically low intake of thiamin, and it presents especially if coupled with a high carbohydrate intake (remember thiamin is needed to convert carbohydrates to energy the body can use). Wet beriberi has the noticeable edema and involves the cardiovascular system more intensely than dry beriberi, in addition to the neuropathy experienced.

Who is at risk of a deficiency?

People who have/have had

  • Bariatric surgery

  • Immunocompromising conditions (i.e. HIV/AIDS)

  • Chronic alcoholics

Symptoms of deficiency

General or Early stages

  • Gastrointestinal: nausea, vomiting, and/or diarrhea, anorexia, indigestion, constipation

  • Cardiovascular and Pulmonary: enlarged heart (cardiomegaly), irregularly fast heart rate (tachycardia)

  • Nervous and Muscular: nerve damage (neuropathy), changes in reflexes, psychological manifestations, degenerative disease (ataxia), malaise, heaviness of legs, weakness, tender calf muscles

  • Eyes and Vision (Ocular): paralysis of the muscles surrounding the eye (ophthalmoplegia), involuntary eye movement (nystagmus)

Infantile Beriberi (2-5 months)

  • Acute: decreased urine output, excessive crying/whining, cardiac failure

  • Chronic: constipation/vomiting, fretfulness, soft and toneless muscles, pallor of skin with cyanosis (blue tint or color to the skin showing a lack of oxygen in the blood)

Dry Berberi

  • Peripheral neuropathy

  • Muscle weakness

  • Cramping (especially lower extremities)

  • Difficulty walking

  • Wernicke-Korsakoff syndrome (with possible neuropathy)

    • Loss of immediate memory

    • Disorientation

    • Nystagmus

    • ataxia

Wet Beriberi

  • Edema (peripheral) of face, legs, trunk, and cavities

  • Tense calf muscles

  • Distended neck veins

  • High blood pressure

  • Decreased urine volume

  • Neuropathy

  • enlarged heart (cardiomegaly)

  • irregularly fast heart rate (tachycardia)

  • Right side heart failure, also affecting the lungs


No upper intake level (UL) has been established for thiamin and no side effects have been reported under 500 mg daily (although staying close to the RDA is recommended as best practice).

Symptoms of Toxicity (in cases of 100 mg given intra- venous or -muscular)


  • Skin irritation

  • Headache

  • Convulsions

  • Cardiac arrhythmia

  • Anaphylactic shock

How to determine levels of thiamin

These tests should be run under direct medical supervision. Ask your doctor and dietitian for more information. You thiamin status can be assessed through measurement of the following:

  • TDP in the blood/urine (blood TDP less than 70 nmol/L may suggest deficiency)

  • Erythrocyte tranketolase activity in hemolyzed while blood (this test measures an enzyme that is dependent on thiamin)

    • >25% increase in activity after adding thiamin to incubation medium indicates deficiency

    • 15-25% suggests adequate status

    • ~120 nmol/L transketolase concentrations used to indicated deficiency

    • 120-150 nmol/L indicates marginal status

  • Blood thiamin concentrations less than 2.5 mcg/dL may suggest deficiency

Urinary thiamin decreases with a thiamin deficiency (since water soluble vitamins are excreted in urine and need to be replenished, therefore in deficiency state the body would try to hold on to or retain this vitamin as much as possible and we wouldn’t see it in the urine in high levels). Amounts less than approximately 40 mcg per day or creatinine (another measure of damage or disease) less than about 27 mcg per gram may suggest a thiamin deficiency.

Sources of Thiamin

Most people are able to get an appropriate amount of this vitamin from their food. Major food sources include pork, sunflower seeds, and legumes.

How stable is Thiamin?

Thiamin content can decrease and the vitamin becomes unstable in the presence of heat, alkali, or oxygen. However, in an acid solution, thiamin becomes heat stable.

Supplementation & Treatment

Thiamin is used to treat inherited metabolic disorders.


FREE Patient Resources

Vitamin B1 (Thiamin)_ Reference_Pt
Download PDF • 2.30MB

Related Professional Resources

Don't you wish you had a quick reference to brush up on thiamin before seeing your clients or patients? This quick reference will help you organize your thoughts and prove to be a great resource in between appointments.   Upon purchase, a high quality pdf file will be available for download. From there, you can turn the file into a print-out, poster, or whatever you would like!


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  1. Pronsky ZM, Elbe D, Ayoob K. Food Medication Interactions (The Foremost Drug-Nutrient Interaction Resource), Micronutrient Food Sources. 18th Edition. 2015. ISBN: 978-0-9710896-6-2

  2. Hart J. Eat Pretty. Chronicle Books. 2014. ISBN 978-1452123660.

  3. Gropper SS, Smith JL, Carr TP. Advanced Nutrition and Human Metabolism, Seventh Edition. Cengage Learning. 2017. ISBN: 978-1305627857.

  4. Mahan KL, Raymond JL. Krause's Food & the Nutrition Care Process 13th Edition. 2011. Saunders. ISBN: 978-1437722338.

  5. Klemm S. What are B-Vitamins? Academy of Nutrition and Dietetics. 2019. Accessed at

  6. Mayo Clinic Staff. Thiamin. 2020. Accessed at

  7. Linus Pauling Institute. Thiamin. Oregon State University. 2020. Accessed at


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