Vitamin B1/Thiamine – Deficiency symptoms and Overdosing

Vitamin B1/Thiamin - Deficiency symptoms and Overdosing

Thiamine is the first of the water-soluble vitamins discovered. Like the other B vitamins, it is necessary for the body’s conversion of carbohydrates into energy and to metabolize fat and protein. There are in the body free thiamine, thiamine monophosphate (TMF), thiamin diphosphate (also called thiamine pyrophosphate, TPF) and thiamine triphosphate (TTF).

Thiamine acts as a cofactor for several enzymes that are included in the body’s conversion of glucose to adenosine triphosphate (ATP) – the form of energy used by all our cells. It is particularly active in the brain and nervous system energy conversion. The vitamin also plays a role in the muscles contraction and nerve signal transmission.

Magnesium is needed for the conversion of thiamine into its biologically active coenzyme form.



Thiamine is absorbed into the small intestine by two mechanisms. In small concentrations, it is absorbed by active transport and at higher concentrations through passive diffusion. It is excreted mainly in the urine as free thiamine and as various hydrolyzed and oxidized products.

The absorption of thiamine decreases and the secretion increases by alcohol consumption. Alcohol also inhibits the conversion of thiamine to coenzyme. Regular intake of larger amounts of tea has also been shown to reduce the amount of thiamin in the body. The reason seems to be the tannins found in tea.


Best sources of thiamine

  • Sunflower seeds
  • Flaxseed
  • Pork
  • Invertebrate
  • Beans
  • Peas
  • Oatmeal
  • Nuts.




Thiamine is destroyed when heated above 212 F / 100 C degrees. For example, by careful heating through steam cooking or light frying, most of the thiamine is retained in the food. As with most vitamins, it is the high-temperature preparation for a longer period of time that destroys vitamin content. The loss of thiamine is up to 60 percent when cooking vegetables and 5-35 percent for baking bread. Thiamine, on the other hand, is resistant to freezing.



The recommended daily intake of vitamin B1 is indicated as 1.1 mg for women and 1.3 mg for men. Clinical data (Study 1, Study 2, Study 3, Study 4) indicate that a daily intake of 100 mg for a longer period of time is safe.



Thiamine is not stored to any great extent in the body and the turnover rate is quite high. Therefore, thiamine deficiency can develop after just 4-5 days if you eat a thiamine-low diet. According to the Swedish Food Administration, however, this is unusual in Sweden. Deficiency occurs only in alcoholics and in rare cases after abdominal or intestinal surgery, in severe anorexia nervosa, regular hemodialysis, long-term diarrhea or extreme one-sided diet.

Thiamine deficiency may also occur in people with hyperthyroidism or HIV infection. In a study, thiamine deficiency was also found in nearly half of 80 patients who had undergone gastric bypass surgery. In those cases, the cause was a bacterial overgrowth of the small intestine.

People with thiamine deficiency becomes less able to digest carbohydrates. It causes a substance called pyruvic acid to accumulate in the blood. Mild thiamine deficiency may manifest as fatigue, insomnia, loss of appetite, headaches, depression, and memory and concentration problems.

Serious thiamine deficiency leads to the disease beriberi, which in adults causes weakness, confusion, weight loss, peripheral neuropathy, edema, difficulty breathing (due to fluid in the lungs), tachycardia and heart failure. In small children, vomiting, cramps, and heart failure are symptoms of beriberi.

Severe thiamine deficiency can also cause Wernick’s encephalopathy, which manifests itself as mental disorders, ataxia, repeated involuntary eye movements and eye paralysis (nystagmus, ocular palsy), as well as Wernicke-Korsakoff syndrome; a chronic neuropsychiatric condition considered to be a consequence of Wernick’s encephalopathy.


Analysis and measurement methods

Thiamin status is often evaluated by measuring the activity of transketolase in hemolyzed whole-blood before and after thiamin diphosphate (TTP) has been added. An increase of more than 15 percent after administration of TTP indicates thiamine deficiency. The level of TTP in red blood cells is also considered to be a useful marker for thiamin status, especially if a deficiency is shown more than once.

Clinical response to thiamine supplementation may also be a useful diagnostic test, especially in situations where a delayed diagnosis can have serious consequences.


Vitamin B1 dietary supplement

Vitamin B1 dietary supplements are in the form of tablets or capsules. The intake of thiamine supplement is better at smaller doses (1-30 mg). The best and most common forms of oral intake are thiamine hydrochloride and thiamine mononitrate, but intramuscular and intravenous treatment is much more effective than oral intake.

Thiamine in the form of propyl disulfide and tetrahydrofurfuryl disulfide are fat-soluble formulations that have better absorption than water-soluble thiamine. They have been used in the treatment of severe neurological diseases and pain.

If an individual B vitamin is taken at a dose exceeding 10 times the RDI for a longer period of time, the intake should be supplemented with a vitamin B complex to avoid the risk of imbalance.



No toxic dose for humans has been confirmed. The risk of injury from overdose is very small. In monkeys, the fatal dose is higher than 350 mg/kg body weight. Excess thiamine is rapidly secreted by the kidneys.

Interactions with drugs

Digoxin: Research suggests that Digoxin, a medicine used to treat heart diseases such as heart failure, cardiac fibrillation, and irregular cardiovascular surgery, can reduce the heart’s ability to pick up and use thiamine.

Diuretics: Some studies have found that the diuretic medications may cause thiamine deficiency due to the increase of the excretion of thiamine through the urine. If thiamine deficiency is detected and corrected, cardiac function may be improved in patients with heart failure.

Antacids (acid neutralizing drugs): Treatment with medicines that neutralize stomach acid may increase the need for thiamine.

Contraceptives, oral: Older studies show that the use of birth control pills may cause mild thiamine deficiency, but newer research is lacking.


Interactions with nutrients

Magnesium: Magnesium is needed for the conversion of thiamine into its biologically active form. There are also some thiamine-dependent enzymes that also require magnesium to function. Therefore, patients with a shortage of both thiamine and magnesium may respond poorly to the addition of thiamine unless the magnesium deficiency is also corrected. Also, note that large doses of thiamine can exacerbate an existing magnesium deficiency.

Vitamin B6(pyridoxine): In a study of 16 children diagnosed with ADHD, whose symptoms had improved when receiving 100 mg of Thiamine 4 times a day, nine of the children received a clear deterioration when taking 100 mg of vitamin B6 (pyridoxine) 3 times a day or more). Interestingly, 10 of the children who were improved when they took vitamin B6 got significantly worse when they also received thiamine.

Alpha-lipoic Acid (ALA): ALA was fatal when injected into the abdominal cavity in rats with thiamine deficiency in a dose of 20 mg/kg body weight. ALA, on the other hand, was not toxic to rats that had no thiamine deficiency. Toxicity could be prevented by the fact that the rats with thiamine deficiency received thiamine prior to treatment with ALA.



Deficiency symptoms: 

  • Fatigue
  • Insomnia
  • Loss of appetite
  • Headaches
  • Depression
  • Memory and concentration problems
  • Less able to digest carbohydrates
  • Serious thiamine deficiency leads to the disease beriberi
  • Severe thiamine deficiency can also cause Wernick’s encephalopathy

No toxic dose for humans has been confirmed

It is necessary for the body’s conversion of carbohydrates into energy and to metabolize fat and protein



  • Alcoholism
  • In rare cases after abdominal or intestinal surgery
  • In severe anorexia nervosa
  • Regular hemodialysis
  • Long-term diarrhea
  • Extreme one-sided diet.

It may also be…

  • Coffee 
  • Birth control
  • Anti-acids
  • Refined grains



-Recommended vitamin B1 supplement by




Gaby, Allan. Nutritional Medicine. Concord, New Hampshire: Fritz Perlberg Publishing; 2011.
Wilhelmsson, Peter. Näringsmedicinska uppslagsboken. 2 rev. uppl. Falun: Örtagårdens bokförlag; 2007.


University of Maryland Medical Center:
U.S. National Institutes of Health: