Vitamin B1 Thiamin Deficency and Toxicity

Vitamin B1 Thiamin Deficency and Toxicity

Thiamin plays a critical role in enabling virtually every aspect of bodily functioning, any deficiency in this vitamin, if not quickly corrected, can have a serious and possibly lasting effect on one’s health. Some of the symptoms associated with deficiency, especially in the early stages, could have other causes while other symptoms can be more specifically traced to inadequate thiamin intake. Rather than attempt to self-diagnose and self-medicate, you should address any concerns you may have with your doctor, who will order the appropriate tests and determine the best course of treatment.


Thiamin can be found in many foods, one reason why many people in this country do not consume enough in their diet is that the American diet is typically heavy in refined flour products, sugar, and coffee that, along with alcohol, deplete vitamin B levels. Prolonged inadequate intake of thiamin can be damaging to the nervous system, gastrointestinal tract, and heart.
Thiamin is well known for its key role in preventing the disease known as beriberi. All the way back in 2600 BC, Chinese physicians were aware of this condition though not about what caused it. Centuries later, outbreaks of beriberi were also very common on sailing voyages until whole grains were included in the sailors’ diet. During the 1920s, researchers finally identified vitamin B1 (thiamin) as the marker both for preventing beriberi and providing the body with a needed source of energy. Today Beriberi is extremely rare in the U.S., but increased understanding of how energy deprivation due to prolonged insufficient thiamin causes this serious disease has furthered medical knowledge of how to prevent and treat other manifestations of thiamin deficiency. Unfortunately, eradicating beriberi completely is probably very difficult, partly because pregnant or breastfeeding mothers who are themselves thiamin deficient, can pass on the condition to their newborn infants. Also, individuals who abuse alcohol for many years are at high risk for developing Wernicke-Korsakoff syndrome, a special form of beriberi that attacks the cerebrum and causes severe damage.(See the section on Symptoms of Deficiency for a more extensive discussion of the different types of beriberi and the characteristic symptoms of each.)
Today, at least in this country, excessive use of alcohol is the leading cause of thiamin deficiency. The perceptual impairment disturbed mental states, and nerve problems that alcoholics present can be possibly attributed to thiamin deficiency. Heavy alcohol use often leads to cirrhosis of the liver that increases the likelihood of thiamin deficiency developing. Other illnesses that can lead to a state of thiamin deficiency include an overactive thyroid, malabsorption disorders, prolonged diarrhea due to serious infection, and certain types of cancer. Heavy use of coffee and tea may be another contributing factor since these beverages act as diuretics that not only remove water from the body but also water-soluble nutrients like thiamin. Teenagers whose diet consists largely of fast foods, soda pop, sweets, and other empty calories are at risk for thiamin deficiency as well. Chronic stress, medications such as antibiotics and diuretics, and smoking also increase a person’s need for thiamin.
Furthermore, many elderly people, particularly those with symptoms of the serious mental disease, such as schizophrenia and dementia, have low blood levels of thiamin. The combination of inadequate diet and impaired digestion and assimilation, besides being the cause of the thiamin deficiency itself, could be an important contributing factor in the development of certain degenerative diseases frequently associated with aging.


Symptoms of thiamin deficiency vary with the degree of severity. Even mild deficiency can produce symptoms because it is already associated with impaired carbohydrate metabolism. Pyruvic acid builds up in the blood, which can lead to decreased utilization of oxygen by the body’s tissues.
The first symptoms of a possible thiamin deficiency may be general enough to have a variety of causes. They include:  
  • Fatigue
  • Loss of appetite.
Since energy production is impaired, the person feels listless. Later, following the appearance of these early symptoms, the individual may become confused, forgetful, clumsy, and depressed. Physiological disturbances such as insomnia, cardiac arrhythmia and slow heart rate, gastrointestinal problems like abdominal pain and constipation, and a weakened immune system and anemia are also likely. As the condition progresses further, and the myelin sheaths surrounding the nerves become damaged, the individual may also experience a prickly sensation (“pins and needles”) in the legs and muscle atrophy and tenderness. If the optic nerve becomes inflamed, vision will be impaired as well. The following is a summary (not a complete list) of the many different kinds of symptoms, besides the fatigue above and loss of appetite, which a deficiency in thiamin can produce.  
  • Irritability
  • Nervousness
  • Malaise
  • Anxiety
  • Depression
  • Insomnia
  • Burning in mouth or tongue
  • Cracks at corners of mouth
  • Indigestion
  • Constipation
  • Weight loss
  • Neuritis (nerve inflammation)
  • Skin disorders—e.g., acne
  • Pallor of skin with cyanosis
  • Hair loss
  • Early graying of hair
  • Heaviness and weakness in legs
  • Tenderness in calf muscles
  • “Pins and needles” in legs
  • Numbness in feet and toes
  • Muscle atrophy and loss of muscle tone
  • Difficulty walking (especially in dry beriberi and cerebral beriberi)
  • Nystagmus (involuntary jerky movements of the eye in cerebral beriberi)
  • Disorientation and impaired short-term memory (in cerebral beriberi)
  • High cholesterol
  • Edema and decreased urine output, along with high blood pressure, tachycardia and heart enlargement (in wet beriberi) leading to heart failure
  • Weakened immune system
  • Anemia


Severe prolonged deficiency of thiamin has been identified as the cause of the otherwise preventable disorder called beriberi. Beriberi comes in four different forms, all of which are very serious.  
  • Infantile (or childhood beriberi)

Infantile beriberi develops in newborn babies who are breastfed by mothers with a thiamin deficiency. It can also occur if the mother was seriously deficient in this vitamin during pregnancy. Infantile beriberi is an extremely serious medical condition because, if left untreated, it can bring the baby’s growth process to a virtual standstill. High pitched screams and a rapid heartbeat are common features. Infantile beriberi can cause cardiac arrest.  
  • Wet beriberi

Wet beriberi is so-called because it is characterized by severe edema in the arms, legs, and feet, which can spread to other parts of the body. Other symptoms include heart enlargement and breathing difficulties. The condition often leads to heart failure. Wet beriberi occurs in adults and is usually associated with a high carbohydrate diet and excessive physical exertion.  
  • Dry beriberi

This form of beriberi also occurs primarily in adults and is characterized by weight loss, severe muscle atrophy, cramps, and tenderness in the legs, and numbness in the feet and toes. There is also nerve degeneration. Dry beriberi is believed to stem from a combination of energy deprivation and insufficient activity.  
  • Cerebral beriberi (also called Wernicke-Korsakoff syndrome)

Cerebral beriberi is usually related to the chronic excessive use of alcohol. In addition to the fact that alcohol itself decreases the bioavailability of thiamin, the diet of alcoholics tends to be low in thiamin. A third contributing factor is that thiamin is actually required for the metabolism of alcohol, so if the little bit available is going primarily for that purpose, there is not enough left over to be used for the body’s more important metabolic processes. Then, on top of all that, a fourth contributing factor is that the excessive use of alcohol causes damage to the liver that adversely affects its ability to convert thiamin to the enzyme TPP. Some people also have a genetic predisposition towards developing cerebral beriberi. Cerebral beriberi causes degeneration of the brain and affects the person’s orientation and ability to walk. In addition to ataxia (staggering gait), the disorder is characterized by paralysis of the eye muscles, nystagmus (involuntary jerky movement of the eyes, poor muscle coordination, confusion, and impaired short-term memory.
Severe thiamin depletion, such as evidenced with a diagnosis of beriberi, can be fatal if not corrected with an improved diet and thiamin supplements promptly. In most instances, natural food supplements are probably a better choice for treating a thiamin deficiency than synthetic supplements because they seem to work more compatibly with other nutrients and are better tolerated. The natural supplements may also contain important enzymes and cofactors and possibly even yet to be discovered additional B complex vitamins.
Fortunately, biochemical changes reflecting inadequate thiamin intake can be detected via blood plasma or serum levels of thiamin or urinary thiamin excretion levels long before an individual reaches the stage of beriberi-type symptoms. Thiamin deficiency, when caught early enough, is treatable.

People Who May Benefit from Additional Amounts of Thiamin

Usually when vitamin B supplements are prescribed or recommended, it is in the form of a vitamin B complex supplement and often as just one component of a multivitamin. In any case, if you have been diagnosed with a thiamin deficiency or fit into one of the following categories, which could increase your risk for developing a deficiency later, you should consult with your doctor. He or she will review your medical history and current situation, order additional tests if necessary, and thereby determine if and to what extent additional amounts of thiamin might benefit you. These are the people who may benefit from additional amounts of thiamin.  
  • People with longstanding fever or diarrhea or serious chronic illnesses, such as diabetes, overactive thyroid, inflammatory bowel syndrome, and cancers of the gastrointestinal tract
  • Alcoholics and smokers:
  • Infants and children who are not getting enough of this nutrient in their regular diet
  • People whose overall nutrition is poor or who have increased nutritional needs
  • Pregnant and lactating women
  • Women taking birth control pills
  • The elderly, especially those with weakened immune systems and congestive heart failure, for which they are taking diuretics
  • People who drink a lot of coffee or tea
  • People with recurrent skin problems
  • People who have had recent surgery
  • People experiencing excessive stress, fatigue, anxiety, nervousness, insomnia, and hyperactivity


The possibility of toxicity concerning thiamin is not something you realistically need to worry about because there is no evidence that it even exists (at least for the amounts ordinarily ingested). Except for folate, which can be toxic at high levels, and vitamin B6, an excess of which can cause neuropathy, the B complex vitamins as a group, even when taken in large amounts, do not appear to be capable of producing a state of toxicity. This is probably because the body does a very efficient job of eliminating any excess.
Possibly the worst thing that could happen with a very large dose of thiamin is that the person becomes overly stimulated or wired. Also, thiamin injections occasionally cause edema. On the other hand, these findings do not rule out the possibility that a truly massive dose of thiamin would be toxic. In fact, it has already been reported that a dose of 100x the RDA given intravenously or intramuscularly has been associated with symptoms such as a headache, convulsions, cardiac arrhythmia, and anaphylactic shock. But there is no legitimate reason to be taking such a mega-dose.
There could be another problem, however, with simply taking a large therapeutic dose of a single vitamin such as thiamin for a long time--a depletion of other B vitamins. Therefore, if it is necessary to take a particular B vitamin such as thiamin in a large amount on a regular basis, it may be best to take it in the form of a complete vitamin B complex supplement.