Merck Manual

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Thiamin Deficiency

(Beriberi; Vitamin B1 Deficiency)


Larry E. Johnson

, MD, PhD, University of Arkansas for Medical Sciences

Last full review/revision Oct 2019| Content last modified Oct 2019
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Thiamin deficiency (causing beriberi and other problems) is most common among people whose diet mainly consists of white rice or highly processed carbohydrates in developing countries and among alcoholics.

  • A diet consisting mainly of white flour, white sugar, and other highly processed carbohydrates can cause thiamin deficiency.

  • At first, people have vague symptoms such as fatigue and irritability, but a severe deficiency (beriberi) can affect the nerves, muscles, heart, and brain.

  • The diagnosis is based on symptoms and a favorable response to thiamin supplements.

  • Thiamin supplements, usually taken by mouth, can correct the deficiency.

The vitamin thiamin (vitamin B1) is widely available in the diet. It is essential for the processing (metabolism) of carbohydrates (to produce energy), proteins, and fats and for normal nerve and heart function. Thiamin is not toxic, so consuming excess amounts of thiamin is not a concern. Good sources of thiamin include dried yeast, whole grains, meat (especially pork and liver), enriched cereals, nuts, legumes, and potatoes.

Thiamin deficiency often occurs with other B vitamin deficiencies.


Thiamin deficiency may result from

  • A deficiency of thiamin in the diet

Young adults with severe anorexia and people whose diet consists mainly of highly processed carbohydrates (such as polished white rice, white flour, and white sugar) may not consume enough thiamin. Polishing rice removes almost all of the vitamins.

People who consume excessive amounts of alcohol often substitute alcohol for food and thus do not consume enough thiamin, are at high risk of developing this deficiency. Also, alcohol may interfere with the absorption and metabolism of this vitamin and may increase the body’s need for thiamin.

Thiamin deficiency may also result from

  • Disorders or conditions that increase the body’s need for thiamin, such as an overactive thyroid gland (hyperthyroidism), pregnancy, breastfeeding, strenuous exercise, and fever

  • Disorders that interfere with the metabolism of the vitamin, such as liver disorders

  • Disorders that prevent thiamin from being absorbed, such as diarrhea that lasts a long time


Early symptoms of thiamin deficiency are vague. They include fatigue, irritability, poor memory, loss of appetite, sleep disturbances, abdominal discomfort, and weight loss.

Eventually, a severe thiamin deficiency (beriberi) may develop, characterized by nerve, heart, and brain abnormalities. Different forms of beriberi cause different symptoms.

Dry beriberi

Nerve and muscle abnormalities develop. Symptoms include a prickling (pins-and-needles) sensation in the toes, a burning sensation in the feet that is particularly severe at night, and leg cramps and pain. Muscles may become weak and waste away (atrophy). If the deficiency worsens, the arms are also affected.

Wet beriberi

Heart abnormalities develop. The heart pumps more blood and beats faster. Blood vessels widen (dilate), making the skin warm and moist. Because the heart cannot continue to work at this level, heart failure eventually develops. As a result, fluid accumulates in the legs (as edema) and in the lungs (as congestion), and blood pressure may fall, sometimes leading to shock and death.

Brain abnormalities

Thiamin deficiency causes brain abnormalities primarily in alcoholics. Brain abnormalities may be present without causing any symptoms until something happens to worsen the thiamin deficiency, such as an alcoholic binge. Brain abnormalities can also cause symptoms after an alcoholic is given carbohydrates intravenously. Symptoms occur because these extra carbohydrates further increase thiamin requirements. These brain abnormalities are called the Wernicke-Korsakoff syndrome, which has two parts:

  • Wernicke encephalopathy causes confusion, apathy, difficulty walking, and eye problems, including involuntary eye movements (nystagmus) and partial paralysis of the eyes. If Wernicke encephalopathy is not promptly treated, symptoms may worsen, resulting in coma and even death.

  • Korsakoff psychosis causes memory loss for recent events, confusion, and a tendency to make up facts to fill in gaps in memories (confabulation).

Infantile beriberi

This form occurs in infants (usually by age 3 to 4 weeks) who are breastfed by a mother who has a thiamin deficiency. In these infants, heart failure may occur suddenly. They may lose their voice (aphonia) to some degree, and they may not have certain reflexes.


  • Physical examination

  • Relief of symptoms when thiamin supplements are taken

The diagnosis of thiamin deficiency is based on symptoms.

Tests to confirm the diagnosis are not readily available. Blood tests to measure electrolyte levels are usually done to exclude other possible causes.

The diagnosis is confirmed if thiamin supplements relieve symptoms.


  • Thiamin supplements

All forms of thiamin deficiency are treated with thiamin supplements. They are usually given by mouth. They are given intravenously if symptoms are severe. Because thiamin deficiency often occurs with other B vitamin deficiencies, multivitamins are usually given for several weeks. People are encouraged to eat healthily and are advised to consume 1 to 2 times the daily recommended intake of vitamins. They should not drink any alcohol.

Wernicke-Korsakoff syndrome, a medical emergency, is treated with high doses of thiamin given intravenously or by injection into a muscle (intramuscularly) for several days. Use of alcohol should be stopped.

When people who may have a thiamin deficiency, particularly alcoholics, must be fed intravenously, they are given thiamin supplements first. These intravenous solutions contain glucose. Because thiamin is needed to process (metabolize) glucose, glucose may trigger or worsen symptoms of thiamin deficiency. Giving them thiamin supplements first can prevent Wernicke-Korsakoff syndrome from developing or worsening.

With treatment, most people recover completely. In some people with Wernicke-Korsakoff syndrome, some brain damage is permanent. Symptoms of beriberi may recur years after apparent recovery.

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