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Vitamin B1 (Thiamin) 101: RDA, Testing, and Supplementing

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Vitamin B1 (Thiamin) 101: RDA, Testing, and Supplementing

Although vitamin B1, also known as thiamin, was not recognized until the 1930s, Chinese literature dating back to 2600 B.C. described B1 deficiency symptoms. B1 was one of the first compounds to be recognized as a vitamin. This article will discuss what vitamin B1 is, including its role in the body, deficiency symptoms, testing, and sources of this important vitamin.


What is Vitamin B1 (Thiamin)?

Vitamin B1, known as thiamin, is a water-soluble vitamin, meaning it's not stored in high amounts in the body. The small amount of storage combined with its rapid metabolism in the body necessitates continuous B1 supplies in our diets. While bacteria in the microbiome of the large intestine reportedly produce B1, the effect of this amount is unknown.

Vitamin B1’s (Thiamin) Role in The Body

B1 has various forms that function as coenzymes. Coenzymes are molecules that are required by enzymes for a reaction to occur. The majority of B1 found in the body is in the form of thiamine diphosphate. Through its coenzymatic actions, B1 affects the breakdown of carbohydrates and amino acids, helping to produce energy (ATP), cholesterol, and neurotransmitters. B1 is also involved in the production of fatty acids, DNA, and RNA.

What Causes Vitamin B1 (Thiamin) Deficiency?

B1 deficiency can be the result of a lack of dietary intake. Certain medical conditions, including HIV/AIDS, diabetes, and alcohol dependence, can lower absorption and increase the excretion of B1, too. People who have had bariatric surgery and older adults are also at an increased risk of B1 deficiency.

Vitamin B1 (Thiamin) Deficiency Symptoms

Berberi disease is the most common result of B1 deficiencies. There are four types of beriberi: dry, wet, cerebral, and gastrointestinal.

Dry beriberi presents primarily as peripheral neuropathies, which is damage to the nerves that are outside of the brain and spinal cord. One of the earlier symptoms is "burning feet syndrome," but exaggerated reflexes, loss of sensation, and muscle weakness can also occur.

Wet beriberi will have neurologic symptoms with the addition of cardiovascular symptoms, including an enlarged heart, rapid heartbeat, swelling, difficulty breathing, and congestive heart failure.

Cerebral beriberi, most often caused by alcohol consumption, can lead to Wernicke's encephalopathy and Korsakoff's psychosis. Wernicke's encephalopathy is diagnosed based on three symptoms: abnormal eye movements, walking difficulties, and cognitive problems. If not treated, Wernicke's encephalopathy can cause Korsakoff's psychosis, characterized by a confused state with severe loss of working and recent memory. These two conditions, Wernicke's encephalopathy and Korsakoff's psychosis, together are referred to as Wernicke-Korsakoff syndrome. When the previous symptoms of Wernicke-Korsakoff syndrome are present, but memory is intact, we refer to that as Wernicke's disease.

Gastrointestinal beriberi results from high lactate levels and, thus, lactic acidosis, causing symptoms of nausea, vomiting, and significant abdominal pain.

How to Test Vitamin B1 (Thiamin) Levels

B1 levels can be assessed in the blood and urine.


B1 levels can be tested in the serum, as offered in the Vitamin B1 test by Access Medical Laboratories, with values ranging from 70-180 nanomoles/liter (nmol/L). Vitamin B1 can also be found on micronutrient tests such as the Micronutrient Test by Spectracell Laboratories.


While not as common as a blood test, B1 levels can be measured in the urine and reflect the amount of dietary B1 intake. Levels in the urine less than 100 micrograms (mcg)/day can indicate insufficient amounts of B1 in the diet, and levels below 40 mcg/day indicate severely low intake levels.

How to Get Enough Vitamin B1 (Thiamin) from Your Diet

The Institute of Medicine has a Food and Nutrition Board that created Dietary Reference Intakes (DRI) measurements for vitamins and minerals. One type of DRI is the Recommended Daily Allowance, defined as the average amount of daily intake required to achieve nutritional adequacy in most of the healthy population. Another DRI, Adequate Intake (AI), is created when there is an insufficient amount of evidence to form an RDA. AIs are defined as the estimated daily amount assumed to reach nutritional adequacy in healthy populations.

AIs have been formed for birth to 1-year-olds. AI for birth to six months is 0.2 mg, and from seven to 12 months is 0.3 mg for both males and females.

Pregnant and lactating women often have different RDAs due to their unique nutritional requirements. The RDA for pregnant and lactating women 14-50 years old is 1.4 mg.

Vitamin B1 sources include food and supplements.

Food Sources of B1 (Thiamin)

B1 is found naturally in certain foods and, in the USA, is a part of enrichments added to foods. About half of dietary B1 is from natural sources, and half is from enriched sources.

Processing foods affects the level of B1. Heating, such as baking and boiling, reduces B1 levels.

Vitamin B1 (Thiamin) Supplements

B1 is also found in supplements, including multivitamins, B vitamin complexes, and as a stand-alone vitamin. Thiamine mononitrate and thiamine hydrochloride are the two most common types of B1 found in supplements as they are stable and water-soluble. Some supplements may contain benfotiamine, a synthetic form of a B1 derivative that will convert into B1 in the body.  



Vitamin B1, or thiamine, is an essential vitamin for the human body. Through its actions as a coenzyme, B1 has the ability to affect a multitude of biochemical processes, from the creation of DNA to the breakdown of carbohydrates. B1 testing can help to rule out deficiencies and ensure proper levels. Knowing dietary and supplement sources of B1 can aid in the prevention of deficiencies and inadequacies.

The information provided is not intended to be a substitute for professional medical advice. Always consult with your doctor or other qualified healthcare provider before taking any dietary supplement or making any changes to your diet or exercise routine.
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