Thiamin is widely available in the diet, particularly in whole grains, meat (especially pork and liver), enriched cereal products, nuts, legumes, and potatoes (see table Sources, Functions, and Effects of Vitamins Sources, Functions, and Effects of Vitamins ). Thiamin is involved in carbohydrate, fat, amino acid, glucose, and alcohol metabolism and is particularly important in the function of central and peripheral nerve cells and the myocardium.
Thiamin is essentially nontoxic.
(See also Overview of Vitamins Overview of Vitamins Vitamins may be Fat soluble (vitamins A, D, E, and K) Water soluble (B vitamins and vitamin C) The B vitamins include biotin, folate, niacin, pantothenic acid, riboflavin (B2), thiamin (B1)... read more .)
Etiology of Thiamin Deficiency
Primary thiamin deficiency is caused by
Inadequate intake of thiamin
It is commonly due to a diet of highly refined carbohydrates (eg, polished rice, white flour, white sugar) in developing countries. It also develops when intake of other nutrients is inadequate, as may occur in young adults with severe anorexia; it often occurs with other B vitamin deficiencies.
Secondary thiamin deficiency is caused by
Increased demand (eg, due to hyperthyroidism, pregnancy, lactation, strenuous exercise, or fever)
Impaired absorption (eg, due to prolonged diarrhea)
Impaired metabolism (eg, due to hepatic insufficiency)
In alcoholics, many mechanisms contribute to thiamin deficiency; they include decreased intake, impaired absorption and use, increased demand, and possibly an apoenzyme defect.
Pathophysiology of Thiamin Deficiency
Thiamin deficiency causes degeneration of peripheral nerves, thalamus, mammillary bodies, and cerebellum. Cerebral blood flow is markedly reduced, and vascular resistance is increased.
The heart may become dilated; muscle fibers become swollen, fragmented, and vacuolized, with interstitial spaces dilated by fluid. Vasodilation occurs and can result in edema in the feet and legs. Arteriovenous shunting of blood increases. Eventually, high-output heart failure may occur.
Symptoms and Signs of Thiamin Deficiency
Early symptoms of thiamin deficiency are nonspecific: fatigue, irritability, poor memory, sleep disturbances, precordial pain, anorexia, and abdominal discomfort.
Different forms of beriberi cause different symptoms.
Dry beriberi refers to peripheral neurologic deficits due to thiamin deficiency. These deficits are bilateral and roughly symmetric, occurring in a stocking-glove distribution. They affect predominantly the lower extremities, beginning with paresthesias in the toes, burning in the feet (particularly severe at night), muscle cramps in the calves, pains in the legs, and plantar dysesthesias. Calf muscle tenderness, difficulty rising from a squatting position, and decreased vibratory sensation in the toes are early signs. Muscle wasting occurs. Continued deficiency worsens polyneuropathy, which can eventually affect the arms.
Wernicke-Korsakoff syndrome, which combines Wernicke encephalopathy Wernicke Encephalopathy Wernicke encephalopathy is characterized by acute onset of confusion, nystagmus, partial ophthalmoplegia, and ataxia due to thiamin deficiency. Diagnosis is primarily clinical. The disorder... read more and Korsakoff psychosis Korsakoff Psychosis Korsakoff psychosis is a late complication of persistent Wernicke encephalopathy and results in memory deficits, confusion, and behavioral changes. Korsakoff psychosis occurs in 80% of untreated... read more , occurs in some alcoholics who do not consume foods fortified with thiamin. Wernicke encephalopathy consists of psychomotor slowing or apathy, nystagmus, ataxia, ophthalmoplegia, impaired consciousness, and, if untreated, coma and death. It probably results from severe acute deficiency superimposed on chronic deficiency. Korsakoff psychosis consists of mental confusion, dysphonia, and confabulation with impaired memory of recent events. It probably results from chronic deficiency and may develop after repeated episodes of Wernicke encephalopathy.
Cardiovascular (wet) beriberi is myocardial disease due to thiamin deficiency. The first effects are vasodilation, tachycardia, a wide pulse pressure, sweating, warm skin, and lactic acidosis. Later, heart failure Heart Failure (HF) Heart failure (HF) is a syndrome of ventricular dysfunction. Left ventricular failure causes shortness of breath and fatigue, and right ventricular failure causes peripheral and abdominal fluid... read more develops, causing orthopnea and pulmonary and peripheral edema. Vasodilation can continue, sometimes resulting in shock.
Infantile beriberi occurs in infants (usually by age 3 to 4 weeks) who are breastfed by thiamin-deficient mothers. Heart failure (which may occur suddenly), aphonia, and absent deep tendon reflexes are characteristic.
Because thiamin is necessary for glucose metabolism, glucose infusions may precipitate or worsen symptoms of deficiency in thiamin-deficient people.
Diagnosis of Thiamin Deficiency
Favorable response to thiamin
Diagnosis of thiamin deficiency is usually based on a favorable response to treatment with thiamin in a patient with symptoms or signs of deficiency. Similar bilateral lower extremity polyneuropathies due to other disorders (eg, diabetes Diabetes Mellitus (DM) Diabetes mellitus is impaired insulin secretion and variable degrees of peripheral insulin resistance leading to hyperglycemia. Early symptoms are related to hyperglycemia and include polydipsia... read more , alcoholism Alcohol Toxicity and Withdrawal Alcohol (ethanol) is a central nervous system depressant. Large amounts consumed rapidly can cause respiratory depression, coma, and death. Large amounts chronically consumed damage the liver... read more , vitamin B12 deficiency Vitamin B12 Deficiency Dietary vitamin B12 deficiency usually results from inadequate absorption, but deficiency can develop in vegans who do not take vitamin supplements. Deficiency causes megaloblastic anemia, damage... read more , heavy metal poisoning) do not respond to thiamin. Single-nerve neuropathies ( mononeuropathies Mononeuropathies Single mononeuropathies are characterized by sensory disturbances and weakness in the distribution of the affected peripheral nerve. Diagnosis is clinical but may require confirmation with electrodiagnostic... read more —eg, sciatica) and multiple mononeuropathies Multiple Mononeuropathy Multiple mononeuropathies are characterized by sensory disturbances and weakness in the distribution of ≥ 2 affected peripheral nerves. (See also Overview of Peripheral Nervous System Disorders... read more (mononeuritis multiplex) are unlikely to result from thiamin deficiency.
Electrolytes, including magnesium, should be measured to exclude other causes. For confirmation in equivocal cases, erythrocyte transketolase activity and 24-hour urinary thiamin excretion may be measured.
Diagnosis of cardiovascular beriberi can be difficult if other disorders that cause heart failure are present. A therapeutic trial of thiamin can help.
Treatment of Thiamin Deficiency
Supplemental thiamin, with dose based on clinical manifestations
Ensuring that dietary supplies of thiamin are adequate is important regardless of symptoms.
Because IV glucose can worsen thiamin deficiency, alcoholics and others at risk of thiamin deficiency should receive IV thiamin 100 mg before receiving IV glucose solutions.
Pearls & Pitfalls
The thiamin dose is
For mild polyneuropathy: 10 to 20 mg orally once a day for 2 weeks
For moderate or advanced neuropathy: 20 to 30 mg/day (as a single or divided dose), continued for several weeks after symptoms disappear
For edema and congestion due to cardiovascular beriberi: 100 mg IV once a day for several days
Heart failure is also treated.
For Wernicke-Korsakoff syndrome, thiamin 50 to 100 mg IM or IV twice a day must usually be given for several days, followed by 50 to 100 mg orally once a day until a therapeutic response is obtained. Anaphylactic reactions to IV thiamin are rare. Symptoms of ophthalmoplegia may resolve in a day; improvement in patients with Korsakoff psychosis may take 1 to 3 months. Recovery from neurologic deficits is often incomplete in Wernicke-Korsakoff syndrome and in other forms of thiamin deficiency.
Because thiamin deficiency often occurs with other B vitamin deficiencies, multiple water-soluble vitamins are usually given for several weeks. Patients should continue to consume a nutritious diet, supplying 1 to 2 times the daily recommended intake of vitamins; all alcohol intake should stop.
The risk of thiamin deficiency is increased in people who subsist on highly refined carbohydrates such as polished rice and white flour (as occurs in developing countries) or who are alcoholics.
Early findings can be nonspecific; peripheral neurologic deficits, high-output heart failure, and Wernicke-Korsakoff syndrome (mainly in alcoholics) may also develop.
Diagnose based on clinical findings, including a favorable response to treatment with supplemental thiamin.