Vitamin B1 (thiamine) helps your body turn food, above all carbohydrates, into energy. In its active form, thiamine diphosphate, it drives key enzymes in the energy metabolism of every cell, which is why the brain, nerves, muscles and heart depend on it most. Vitamin B1 contributes to normal energy-yielding metabolism, normal functioning of the nervous system, normal psychological function and the normal function of the heart. Adults need about 1.0 to 1.3 mg a day.
Key facts about vitamin B1
- Daily need (D-A-CH reference values): 1.0 mg for women and 1.1 to 1.3 mg for men, depending on age; 1.2 to 1.3 mg from the second trimester of pregnancy and 1.3 mg while breastfeeding.
- The nutrient reference value (NRV) used on EU and Swiss labels is 1.1 mg.
- No tolerable upper intake level has been set; surplus thiamine from food and usual supplements is excreted in the urine.
- The body holds only about 25 to 30 mg, so stores run low within a few weeks if intake stops.
- Good sources per 100 g: wheat germ about 1.9 mg, sunflower seeds about 1.5 mg, lean pork 0.6 to 1 mg, oat flakes about 0.6 mg.
What does vitamin B1 do in the body?
Thiamine is absorbed in the small intestine and converted into thiamine diphosphate (also called thiamine pyrophosphate). This coenzyme is needed by several enzymes that sit at the centre of energy production:
- Pyruvate dehydrogenase links the breakdown of glucose to the citric acid cycle, the main energy pathway in the cells.
- Alpha-ketoglutarate dehydrogenase is a step inside the citric acid cycle itself.
- Transketolase works in the pentose phosphate pathway, which supplies building blocks for DNA and RNA.
- Branched-chain keto acid dehydrogenase breaks down the amino acids leucine, isoleucine and valine.
Nerve cells and the brain run almost entirely on glucose, and the heart muscle never rests. That is why these tissues are affected first when vitamin B1 runs short. Thiamine also has a role in the nerve cell membranes and in the conduction of nerve signals.
In the EU and Switzerland, the following health claims are authorised. Vitamin B1 (thiamine) contributes to:
- normal energy-yielding metabolism;
- normal functioning of the nervous system;
- normal psychological function;
- the normal function of the heart.
Thiamine works alongside the other B vitamins in the same pathways. Read how it fits in with the group in what each B vitamin does, and in the partner article on pantothenic acid (vitamin B5), the vitamin that makes coenzyme A for the same energy cycle.
Why is vitamin B1 important? The lesson of beriberi
Vitamin B1 was the first B vitamin to be discovered, and the story explains why it matters. In the late 19th century, beriberi, a disease of nerves and heart, was widespread in East Asia, including in the Japanese navy, where sailors lived largely on polished white rice. The naval doctor Kanehiro Takaki changed the rations to include more barley, meat and vegetables, and cases dropped sharply. In the Dutch East Indies, Christiaan Eijkman then observed that chickens fed polished rice developed similar symptoms, while those fed unpolished rice did not. The protective substance in the rice husk was later isolated and named thiamine.
Polishing removes the bran and germ, where most of the grain's vitamin B1 sits. The same principle still applies today: wholegrain foods provide far more thiamine than refined white flour or white rice.
Which foods are high in vitamin B1?
Thiamine is found in whole grains, seeds, nuts, legumes and pork. Many plant foods are good sources, so a vegan or vegetarian diet based on whole foods covers the need well.
| Food | Vitamin B1 per 100 g (approx.) |
|---|---|
| Wheat germ | 1.9 mg |
| Flaxseed | 1.6 mg |
| Sunflower seeds | 1.5 mg |
| Macadamia nuts | 1.2 mg |
| Pork, lean, cooked | 0.6 to 1 mg |
| Oat flakes | 0.6 mg |
| Wholemeal bread | 0.3 mg |
| Green peas, cooked | 0.3 mg |
| Brown rice, cooked | 0.2 mg |
| Lentils, cooked | 0.2 mg |
| Potatoes, boiled | 0.1 mg |
| White rice, cooked (not fortified) | 0.02 mg |
Thiamine is water-soluble and sensitive to heat, so part of it passes into cooking water and is lost with long cooking. Sulphites, used as preservatives, also destroy it. Raw freshwater fish and shellfish contain enzymes (thiaminases) that break thiamine down, and large amounts of tea and coffee can reduce its uptake. For most people these effects are small, but they add up in a diet that is already low in vitamin B1. In Switzerland flour is generally not fortified with thiamine, so whole grains matter more than in countries such as the USA, where refined flour is enriched.
How much vitamin B1 do you need per day?
The reference values for Germany, Austria and Switzerland (D-A-CH) are based on energy needs, so they are slightly higher for younger men:
| Group | Women | Men |
|---|---|---|
| 19 to under 25 years | 1.0 mg | 1.3 mg |
| 25 to under 51 years | 1.0 mg | 1.2 mg |
| 51 to under 65 years | 1.0 mg | 1.2 mg |
| 65 years and older | 1.0 mg | 1.1 mg |
| Pregnancy, 2nd / 3rd trimester | 1.2 / 1.3 mg | |
| Breastfeeding | 1.3 mg |
The European Food Safety Authority (EFSA) expresses the need per unit of energy: 0.1 mg of thiamine per megajoule (MJ) for all adults. Because the body cannot store much, a steady daily intake matters more than occasional large amounts.
Vitamin B1 deficiency: symptoms and who is at risk
A mild shortfall shows up with signs that are easy to overlook: loss of appetite, weight loss, tiredness, irritability, low mood, poor concentration and memory problems. If the deficiency continues, it affects the nerves and the heart:
- Dry beriberi: tingling, burning or numbness in the feet and legs, muscle weakness and reduced reflexes.
- Wet beriberi: a fast heartbeat, breathlessness and swelling of the legs, which can lead to heart failure.
- Wernicke encephalopathy: confusion, an unsteady gait and abnormal eye movements. This is a medical emergency; without prompt thiamine given by a doctor it can progress to Korsakoff syndrome with lasting memory loss.
Who is at risk?
- People with alcohol dependence: alcohol reduces the intake, absorption and storage of thiamine. This is the most common cause in Europe.
- After bariatric surgery and in conditions with long-lasting vomiting, including severe morning sickness (hyperemesis gravidarum).
- People with diabetes, who lose more thiamine in the urine.
- Older adults with a low food intake, and people on dialysis.
- Long-term use of some medicines, such as loop diuretics (for example furosemide), which increase losses in the urine.
Thiamine status is measured with a blood test (thiamine diphosphate in whole blood). If you belong to a risk group or have symptoms like these, speak to your doctor; do not self-diagnose. Tiredness has many causes, and our guide to which deficiencies make you tired covers the most common ones.
Can you take too much vitamin B1?
From food and usual oral supplements, practically not. Neither EFSA nor the US National Academies have set an upper limit, because no adverse effects have been shown even with oral doses many times the requirement; the kidneys excrete what is not needed. Rarely, very high doses can cause stomach upset. Allergic reactions have been reported mainly after injections, which are given only under medical supervision. High-dose single products are not needed by healthy people, so discuss them with your doctor or pharmacist.
Should you take a vitamin B1 supplement?
If you eat a varied diet with whole grains, legumes, nuts and seeds, you are unlikely to need extra thiamine. Supplements make sense mainly for the risk groups above, and in that case a doctor should set the dose. For everyone else, a multivitamin that provides around the reference intake of vitamin B1 together with the other B vitamins can help to reach daily needs consistently.
Vitamin B1 in Sanbera formulas
All four Sanbera formulas contain vitamin B1. Per daily serving of three tablets, Daily Essential Women, Daily Essential Men, Nightly Reload Women and Nightly Reload Men each provide 0.83 mg of thiamine (75% NRV). Combining a Daily and a Nightly formula gives 1.66 mg, well within a safe range. Vitamin B1 contributes to normal energy-yielding metabolism, normal functioning of the nervous system and the normal function of the heart. The formulas are vegan and made in Switzerland.
Frequently asked questions
Is vitamin B1 good for the nerves?
Vitamin B1 contributes to the normal functioning of the nervous system, because nerve cells depend on glucose for energy and need thiamine to use it. A deficiency can cause tingling, burning and weakness in the legs. High-dose thiamine and benfotiamine have been studied for nerve pain, for example in diabetes, with mixed results; that is a question for your doctor.
What does vitamin B1 do for the heart?
Vitamin B1 contributes to the normal function of the heart. The heart muscle beats continuously and needs a constant supply of energy, which thiamine helps to release from glucose. Severe deficiency can cause wet beriberi with a fast heartbeat, breathlessness and swollen legs. More on nutrients and the heart in our article on vitamins and minerals for a healthy heart.
Why do people with alcohol problems need vitamin B1?
Alcohol reduces the absorption of thiamine in the gut, lowers how much the liver can store and increases losses, while heavy drinkers often eat less. Thiamine deficiency is therefore common in alcohol dependence and can lead to Wernicke encephalopathy, a serious brain disorder. During alcohol withdrawal, doctors routinely give thiamine, usually at high doses and often by injection.
Is vitamin B1 the same as vitamin B12?
No. Vitamin B1 (thiamine) and vitamin B12 (cobalamin) are two different B vitamins. Both contribute to normal functioning of the nervous system and energy-yielding metabolism, but B12 is also needed for red blood cell formation and is found naturally only in animal foods, while B1 is plentiful in plant foods. Read more about vitamin B12 and its deficiency signs.
Does vitamin B1 keep mosquitoes away?
There is no good evidence for this popular idea. The theory is that thiamine changes the smell of your skin, but a controlled study at the University of Wisconsin found that taking vitamin B1 did not make people less attractive to mosquitoes. Authorities do not recommend vitamin B1 as a repellent; use a tested insect repellent and protective clothing instead.
Why is thiamine called the morale vitamin?
In the 1930s and 1940s, thiamine was nicknamed the "morale vitamin" because people with low intakes in early studies became irritable, depressed and unable to concentrate. Today the authorised wording is that vitamin B1 contributes to normal psychological function. Extra thiamine does not improve mood in people whose intake is already adequate.
Sources
- National Institutes of Health, Office of Dietary Supplements: Thiamin, Health Professional Fact Sheet
- EFSA Panel on Dietetic Products, Nutrition and Allergies (2016): Dietary Reference Values for thiamin
- German Nutrition Society (DGE): Reference values for thiamin
- European Commission: EU Register of nutrition and health claims
- U.S. Department of Agriculture: FoodData Central (food composition values)
This article is for general information and does not replace advice from a doctor or pharmacist. Food supplements are not a substitute for a varied, balanced diet and a healthy lifestyle.