Vitamin B1 deficiency can lead to fatigue and several serious diseases

An estimated 2.2 billion people worldwide are deficient in vitamin B1, which is primarily caused by an unbalanced diet, excessive consumption of coffee or tea, various medications, environmental toxins, and genetic defects. The same applies to high alcohol intake, where long-term abuse can lead to life-threatening brain inflammation. Evidence suggests that higher doses of vitamin B1 in supplement form may have a beneficial effect on many symptoms and diseases.

Vitamin B1 (thiamine) is a water-soluble vitamin, and since the body cannot store it, a daily intake is required. Vitamin B1 primarily functions as a cofactor for many enzymes and is essential for cellular energy metabolism, including the metabolism of glucose (blood sugar), fats, and amino acids. Vitamin B1 is important for the integrity and repair of DNA, as well as for the nervous system, cognitive functions, the heart, circulation, muscles, digestion, and sleep quality. In addition, vitamin B1 helps counteract oxidative stress and chronic inflammation, which are involved in most chronic diseases. Vitamin B1 specifically plays a role in the selenium-containing antioxidants GPX and Txnrd. It also helps bind excess iron, thereby preventing the formation of hydroxyl radicals, which are among the most harmful free radicals.
In a recent review article, the authors therefore examined the role of vitamin B1 in health and in the development of a wide range of diseases. They also looked more closely at how very high doses may have beneficial effects on various genes and diseases.

Deficiency diseases and symptoms

Because vitamin B1 is essential for cellular energy metabolism, the first symptoms of deficiency are often nonspecific and depend on which cells lack energy. Common deficiency symptoms include chronic fatigue, mood swings, depression, irritability, difficulty concentrating, brain fog, poor memory, loss of appetite, digestive problems, and sleep disturbances. A 2018 study showed that vitamin B1 deficiency may be associated with cardiovascular disease, diabetes, and mental disorders.
Another population study found a significant deficiency of vitamin B1 among cancer patients.
Severe deficiency results in the classic deficiency disease beriberi, which occurs in two forms. Wet beriberi leads to a weakened heart and fluid retention in the body. Without treatment, the condition can result in life-threatening heart failure. Dry beriberi is seen primarily in individuals with alcoholism and is characterized by neuritis, muscle weakness, and gait disturbances. Alcoholism itself lowers blood levels of vitamin B1 and simultaneously impairs the function of vitamin B1 transporters in the brain. Wernicke’s encephalopathy, an acute and life-threatening brain inflammation, is often caused by prolonged alcohol abuse. The condition frequently occurs together with Korsakoff’s syndrome, which is characterized by permanent memory impairment.

Sources of vitamin B1 and causes of widespread deficiency

Good sources of vitamin B1 include a varied diet rich in whole grains, seeds, nuts, mushrooms, garlic, beans, other vegetables, as well as meat, organ meats, and fish. Although it should be easy to obtain sufficient vitamin B1 by eating a healthy diet, it is estimated that 30% of the world’s population is deficient, primarily due to excessive intake of ultra-processed foods and beverages.
Persistently elevated blood sugar levels, which are common due to high carbohydrate intake, can lead to increased loss of vitamin B1 through urine.
Chronic inflammation, which characterizes many chronic diseases, also reduces the body’s vitamin B1 levels.
Diuretics, acid-reducing medications, and excessive consumption of tea, coffee, and alcohol can make it more difficult to absorb or utilize the vitamin.
Environmental toxins such as lead, mold, and microplastics may also impair absorption and utilization. The same applies to genetic factors, which may be either inherited or acquired.

Higher doses for specific diseases and alcoholism

The official recommended daily intake of vitamin B1 is between 1.1 and 1.3 mg, which should be easy to obtain from a healthy diet. However, according to several researchers, this is not always sufficient to optimize the body’s vitamin B1 status, and for this reason, much higher doses have been used in cases of deficiency symptoms and various diseases.
As an initial approach, supplementation with 100 mg of vitamin B1 one to three times daily may be considered in individuals who have great difficulty waking in the morning, experience daytime fatigue, or have poor sleep.
Studies have shown that higher doses corresponding to 300 mg daily may have a beneficial effect on blood pressure in individuals with elevated blood sugar. It is also assumed that such higher doses may help lower blood sugar in individuals with early signs of metabolic syndrome, thereby contributing to the prevention of type 2 diabetes. In addition, 400 mg of vitamin B1 daily may be considered as adjunct therapy in connection with stroke.
A research team from Aarhus University Hospital found in a placebo-controlled study that very high doses ranging from 600 to 1,800 mg daily may alleviate chronic fatigue in patients with the chronic intestinal diseases Crohn’s disease and ulcerative colitis. The highest doses were given to men and adjusted according to body weight.
It is possible that very high doses of vitamin B1 may also be effective in other forms of chronic fatigue. Although the exact mechanisms are not known, it is assumed that high doses compensate for defective enzyme function, including the transport of vitamin B1 from the blood to the energy-producing mitochondria in brain cells and elsewhere.
It is therefore assumed that high doses of vitamin B1 may affect the brain and nervous system by improving energy metabolism, blood flow, reducing high blood pressure, decreasing local inflammation, and increasing the synthesis of the neurotransmitter dopamine, which plays a role in mood and motivation.
For reference, vitamin B1 supplements should be taken separately from acid-reducing medications, and it is also advisable to ensure adequate intake of other B vitamins due to multiple interactions.
In cases of severe deficiency, such as Wernicke-Korsakoff syndrome and certain chronic intestinal diseases, vitamin B1 is administered by injection to achieve a faster effect.

Facts about vitamin B1, its different forms, and supplementation

• In plants, vitamin B1 is found in a non-phosphorylated form
• In human and animal tissues, vitamin B1 is found in phosphorylated active forms
• Thiamine diphosphate (TDP) is the primary form involved in energy transfer and regulation of various metabolic functions
• The highest concentrations of vitamin B1 are found in muscles, heart, brain, liver, and kidneys
• Higher doses are generally safe, as excess vitamin B1 is excreted in the urine
• Very high doses, especially injections, may in rare cases cause nausea, gastrointestinal discomfort, restlessness, and allergic reactions
• It is generally advisable to divide higher doses throughout the day
• Vitamin B1 is available in several forms in dietary supplements
• The most common standard forms are thiamine hydrochloride and thiamine mononitrate

References:

Julia Kazmierczak-Baranska et al. Thiamine (vitamin B1) – An Essential Health Regulator. Nutrients 2025

Simone Passarelli et al. Global estimation of dietary micronutrient inadequacies: a modeling analysis. The Lancet Global health. 2024

Palle Bager et al. Randomized clinical trial: High-dose oral thiamine versus placebo for chronic fatigue in patients with quiescent inflammatory bowel disease. Alimentary Pharmacology and Therapeutics. 2020