Vitamin B1 (Thiamine): Benefits, Foods, Deficiency, B1-B6 and Dosage (The Complete 2026 Guide)

★ Thiamine 10 mg per capsule

B Complex Vitamins (30 capsules)

Vitamin B1 never works alone: it produces energy with B2 and B3, and becomes active through magnesium. Our complex brings together all eight B vitamins in active forms, including 10 mg of thiamine, in a daily vegetable capsule made in France.

8 B vitamins Active forms 1 capsule per day Vegan

Discover the B Complex Vitamins →

1. Thiamine, TDP: the glucose vitamin

The story of vitamin B1 begins with a colonial puzzle. In the 19th century, Asia sees an explosion of a disease that paralyzes and causes death from heart failure: beriberi. beriberiIn 1897, a Dutch military physician in Java, Christiaan Eijkman, notices that his chickens fed white rice develop a paralysis that heals as soon as they're given whole grain rice again. The cause was not a microbe, as everyone thought, but the absence of something. This "something," isolated in 1926 and named thiamine, became the first identified vitamin and earned Eijkman the Nobel Prize in 1929. This discovery gave birth to the very concept of vitamins and to the numbering that logically begins with B1.

In the body, thiamine doesn't work as-is: it is phosphorylated into thiamine diphosphate (TDP, also called thiamine pyrophosphate), its active form, a reaction that requires magnesium. This apparently technical detail has major clinical consequences that we will encounter in section 7. TDP then serves as a coenzyme for three central enzymes:

• pyruvate dehydrogenase, which allows the glucose digestion product to enter the cell's energy center; if it blocks, pyruvate transforms into lactate, hence the lactic acidosis of severe deficiencies;
• alpha-ketoglutaratedehydrogenase, a step in the Krebs cycle, the loop that produces most of our energy;
• transcetolase , which fuels the pentose phosphate pathway, supplier of DNA building blocks and antioxidant power in cells. The activity of this enzyme in red blood cells is historically used to measure B1 status.Two practical consequences flow from this biochemistry. First, thiamine is the

sugar vitamin : the more the body burns carbohydrates, the more it consumes. Second, the tissues most dependent on glucose are the most vulnerable: the brain, which consumes one-fifth of everything we absorb, peripheral nerves, and heart muscle. This explains why deficiency produces a neurological and cardiac picture, not, for example, a skin one. This also explains a phenomenon that has cost patients their lives: infusing glucose to a deficient person before giving them thiamine consumes their last reserves at once and can trigger acute encephalopathy. The order matters. 2. What is vitamin B1 for? The claims recognized by EFSA

Key takeaways

European Regulation No. 432/2012 authorizes four claims for thiamine, provided the product contains at least 15% of the NRV (0.165 mg) per serving. Vitamin B1 contributes to:

• normal energy metabolism ;
• normal functioning of the nervous system ;
• normal psychological functions ;
• normal heart function.

The last one deserves special attention, because it is unique. No other B vitamin carries a cardiac claim, and very few nutrients in general. EFSA granted it on the basis of a simple reasoning: thiamine deficiency causes documented cardiac insufficiency for more than a century, wet beriberi, reversible with treatment. The heart muscle beats continuously and derives most of its fuel from glucose and fatty acids; when pyruvate dehydrogenase is blocked, it finds itself in permanent energy deficit, blood vessels dilate, blood flow increases to compensate, and the heart eventually fails. We detail this mechanism and its modern implications in section 8.

3. How much vitamin B1 per day? A requirement proportional to calories

This proportionality to calories has a consequence that few people realize: a diet high in simple sugars and refined products increases the need for thiamine while providing little vitamin, since refining has removed it. A high-calorie diet based on sodas, white bread, and processed foods is, in theory, the worst possible intake-to-requirement ratio. Conversely, an athlete who eats a lot but varied foods naturally meets their increased needs, because the whole foods they consume in large quantities provide it proportionally. This is also why alcoholics combine all the risk factors: alcohol provides empty calories that increase the requirement, while blocking the absorption of the vitamin. Like biotin,

no upper safety limit has been set for oral intake: intestinal absorption is saturable beyond approximately 5 mg per dose, the remainder is simply not absorbed, and what does pass is eliminated in the urine. Medical doses of 100 to 500 mg per day, or even more by injection in Gayet-Wernicke encephalopathy, are well tolerated, with very rare allergic reactions to the injectable form. This safety profile explains an emergency medicine principle: when in doubt, treat first. 4. Foods rich in vitamin B1 (and what destroys it)

Key takeaways

Thiamine is the most fragile of the B vitamins, and four enemies lie in wait for it. First, refinement : hulling rice or bolting flour removes the germ and bran, where it concentrates, with losses of 70 to 80%. This is exactly what triggered beriberi epidemics in Asia when rice polishing machines spread, and this is why many countries now enrich flour. Then heat and water : thiamine is water-soluble and heat-sensitive, losses reach 25 to 50% when boiling in water, much less with steaming or if you reuse the cooking liquid. And baking soda, sometimes added to soften legumes or preserve the color of vegetables, destroys it almost completely in an alkaline environment.

And finally, antithiamines , the least known. The thiaminases from raw fish and shellfish break down the vitamin; deficiencies have been described in heavy consumers of raw fish, and especially in farmed cats and foxes fed this way, which helped understand the mechanism. Cooking destroys them, so the occasional sushi poses no problem. The sulfites, used as preservatives in wine, light dried fruits and certain industrial preparations, also break down the molecule. Tea and coffee in large quantities, betel leaves and certain plants contain polyphenols that oxidize it. None of these factors pose a problem on their own in a varied diet; they matter when they add up to already low intakes.

5. Deficiency and beriberi: the two faces of insufficiency

Before these established presentations, early deficiency manifests through signs that no one links to a vitamin: fatigue, irritability, loss of appetite, concentration and working memory problems, heavy legs, cramps, sometimes nausea and constipation. This is what French authors call marginal deficiency, which they acknowledge has poorly established clinical consequences (Guilland, Rev Prat, 2013). This ambiguity explains part of the marketing around B1: these symptoms are so common they can be attributed to anything.

Should we be concerned in France? Available data suggest not for the general population. A Japanese study of 270 independent adults aged 25 to 97 years found no cases of deficiency or even borderline values, with no age-related differences, whereas the reported prevalence is 2 to 6% in Europe and the United States (Uchida, Cureus, 2023). Risk is concentrated in specific situations, detailed in the following section.

6. Alcohol, bariatric surgery, vomiting: who is really at risk

The particularity of thiamine is that the body stores almost none: approximately 25 to 30 mg total, essentially in muscle, liver, heart and brain, or two to three weeks of consumption. This is the shortest reserve of all B vitamins, compared to the three to five year reserves of vitamin B12. An interruption in intake of just a few weeks is therefore enough to create true deficiency, which explains the rapid onset of severe presentations.

Alcohol is the leading cause in wealthy countries, and it works through multiple mechanisms simultaneously: alcoholic beverages provide calories without vitamins, increasing the need; alcohol blocks the intestinal transporter of thiamine; it reduces its conversion to active form in the liver and its storage; and it is often accompanied by unbalanced nutrition. A systematic review of homeless people with heavy alcohol consumption found B1 deficiency prevalence rates up to 51% depending on studies, the most frequently deficient vitamin of all those measured (Ijaz, Int J Equity Health, 2017).

The message of this series is essential for a population that has nothing to do with the stereotypical image of vitamin deficiency: young women and men, often otherwise in good health, who vomit after their surgery and to whom no one thinks to give thiamine. The typical timeframe is one to three months after the procedure. The rule, in France as elsewhere, is systematic vitamin supplementation after bariatric surgery, for life, and absolute vigilance in the face of any vomiting that lasts more than a few days. The same logic applies to severe vomiting in pregnancy (hyperemesis gravidarum), a classic cause of encephalopathy in young women, and to eating disorders with malnutrition, where too-rapid refeeding (refeeding syndrome) can trigger it.

Other situations deserve to be recognized: long-term diuretic treatment for heart failure, which increases urinary thiamine losses (section 8); dialysis ; chronic vomiting regardless of its cause;prolonged hospitalization, where status deteriorates even in patients who are eating, as demonstrated by a Japanese study of 471 hospitalized elderly people, of whom 84% saw their thiamine drop in one week; and infants breastfed by a thiamine-deficient mother, still a cause of infant mortality in Southeast Asia. Non-bariatric digestive surgery , cancers and pancreatitis complete the list (Kohnke et Meek, Ann Clin Biochem, 2020).

7. Why vitamin B1 and B6 in alcohol withdrawal?

"Why B1 and B6 in withdrawal" is one of the most frequently asked questions about this vitamin, and the answer comes in three parts.

B1 because withdrawal can kill neurons. A chronic drinker enters withdrawal with thiamine reserves nearly empty. However, stopping alcohol, resuming food intake, and glucose infusions suddenly ramp up sugar metabolism, thus thiamine consumption. If reserves are empty, pyruvate dehydrogenase becomes blocked where glucose is most abundant, in specific brain regions (mammillary bodies, thalamus, around the third ventricle), and Gayet-Wernicke encephalopathy is triggered, sometimes within hours. Hence the absolute rule in emergency medicine: thiamine before glucose, never the reverse, and in high doses by parenteral route, without waiting to confirm the diagnosis, since the vitamin is harmless and delay, meanwhile, leaves permanent amnesia (Mateos-Díaz, Med Clin, 2022).

B6 because the deficit is present here too, and the brain needs it to calm down. Alcohol lowers vitamin B6 through a documented mechanism: acetaldehyde, its breakdown product, displaces the active form from its carrier proteins and accelerates its destruction. However, pyridoxal-5-phosphate is essential for the manufacture of GABA, the main inhibitory neurotransmitter, precisely the one whose system is dysregulated during withdrawal: alcohol stimulated it artificially, its cessation leaves a hyperexcitable brain, hence anxiety, tremors and seizure risk. Correcting B6 does not replace withdrawal medications, but is part of restoring the body's equilibrium. Our vitamin B6 guide details its role and reminds that, unlike B1, it has a safety ceiling not to be exceeded.

Magnesium, the forgotten piece. The transformation of thiamine into its active form requires magnesium, and chronic drinkers are almost always deficient in it. This is a point that clinicians regularly highlight: a patient who does not respond to thiamine may simply be suffering from hypomagnesemia, a situation worsened by the frequent association of proton pump inhibitors and diuretics (Wijnia, 2022). In hospital practice, magnesium, thiamine, B6 and vitamin PP form the quartet of withdrawal management. In daily practice, this reminds us of one simple thing: B vitamin supplementation makes little sense if magnesium status is low. Our Magnesium+ combines a microencapsulated bisglycinate, malate and taurine with 2 mg of vitamin B6.

A word about "B1-B6 vitamin therapy", which is highly sought after: under this name circulate pharmaceutical products combining the two vitamins, prescribed for neuropathies, pain and withdrawal support. These are medications, with doses far exceeding supplements and, for B6, a safety limit to respect since prolonged high-dose supplementation can itself cause neuropathy. A dietary supplement of B vitamins at nutritional doses does not operate in this category and does not claim to replace it.

8. Heart, diuretics and heart failure

The heart muscle beats one hundred thousand times a day without interruption, making it one of the most energy-hungry tissues in the body. When thiamine is lacking, energy production from glucose is blocked, heart cells become exhausted and peripheral vessels dilate; the heart compensates by increasing its output, until it can no longer. This mechanism, described for a century as wet beriberi, manifests as shortness of breath, edema and a rapid pulse, and it regresses within days on thiamine, making it one of the rare reversible heart failures.

The topic returned through an unexpected door: loop diuretics (furosemide, bumetanide), the cornerstone of heart failure treatment, increase the urinary elimination of thiamine. Research has found low levels in a notable proportion of heart failure patients on long-term treatment, who often also have advanced age, decreased appetite and a salt-restricted diet that is sometimes monotonous. Several small supplementation trials showed improvement in ejection fraction, but they involved only dozens of patients, with heterogeneous methodologies and inconsistent results. Cardiology guidelines have not adopted systematic supplementation, while recommending considering it when heart failure worsens without explanation in a malnourished patient or one on high doses of diuretics.

A word about sepsis, where thiamine made headlines. A protocol combining vitamin C, thiamine and hydrocortisone had sparked enormous hope following spectacular preliminary results. The confirmatory randomized trial dampened that enthusiasm.

The lesson extends beyond intensive care: a vitamin whose deficiency causes a disease is not necessarily a treatment for that disease when deficiency is not the cause. This is true for the heart, sepsis, and most of the promises surrounding B vitamins.

9. Benfotiamine and diabetic neuropathy

Ordinary thiamine is absorbed by a saturable intestinal transporter: beyond a few milligrams per dose, the excess simply doesn't enter. The benfotiamine circumvents this limit. This fat-soluble derivative, synthesized in Japan in the 1950s, crosses the intestinal wall by diffusion, is then converted to thiamine in the body, and raises blood and tissue concentrations far more than the water-soluble form at equal dose. It's not a "better" vitamin, it's a vitamin better delivered.

The interest focused on diabetes, for a mechanistic reason. Chronic excess glucose overwhelms the sugar degradation pathways and produces compounds toxic to nerves and blood vessels, including the famous advanced glycation end products. Now transketolase, the thiamine-dependent enzyme, diverts this surplus toward a harmless exit pathway. By stimulating this enzyme, benfotiamine would reduce the formation of deleterious compounds. Moreover, diabetics frequently have reduced thiamine status due to increased urinary loss.

Two nuances are warranted. On one hand, the positive trials are modest in size and short in duration, focusing mainly on symptoms (pain, tingling) rather than on the progression of nerve damage; the authors themselves call for longer-term trials to confirm. On the other hand, benfotiamine is in Europe a medication in certain countries and not a dietary supplement, at doses of 150 to 600 mg per day: it falls under medical prescription, not self-medication. To cover a nutritional need, thiamine hydrochloride or thiamine mononitrate, at a few milligrams, do exactly the same job for a fraction of the price.

10. Sleep, mood, energy: what is true and what is not

"Vitamin B1 and sleep" is a frequent search query, and the association is not absurd: thiamine carries the claim "contributes to normal psychological functions," its deficiency causes irritability, anxiety, concentration problems and fragmented sleep, and it appears in most market "relaxation" or "anti-stress" formulas. But two very different claims must be distinguished. Correcting a deficiency improves these symptoms : this is established, and it is even one of the ways deficiency was historically described. Adding B1 to someone who is not deficient improves their sleep : this is not shown by any trial.

A few older studies on small samples reported improved mood and alertness in supplemented young women, without these results being reproduced on a large scale. Recent literature on thiamine and sleep is limited to deficient or hospitalized populations. If your sleep is deteriorating, the levers with documented efficacy are elsewhere: schedule regularity, morning light, screens and evening light, caffeine after 2 PM, alcohol in the evening (which fragments sleep and, incidentally, depletes thiamine), and for the nutritional aspect, magnesium, which several trials support for its effect on stress and sleep quality in people with low status. Our chronic fatigue guide details the nutrients that actually have data, and our Optimal Sleep relies on other active ingredients than B vitamins.

The same reasoning applies toenergy and sports performance. Thiamine enables glucose to be burned, so an athlete deficient in it sees performance drop; but in an athlete with normal status, B vitamin supplementation trials have not shown gains in endurance or power. What is true, however, is that the requirement increases with energy expenditure (section 3): an athlete at 4,000 kcal needs about 4 mg of thiamine per day, which abundant and varied food naturally provides, but which a high-calorie diet based on refined products may not cover. It is there, and only there, that additional supplementation makes sense.

11. The myths: mosquitoes, weight loss, megadoses

12. Forms, blood dosage, and interactions

How is status measured? Two methods coexist: measurement of thiamine diphosphate in whole blood by chromatography, and the activity of red blood cell transketolase before and after thiamine addition, with the gap reflecting the deficiency. A recent study conducted in Laos on over 500 children compared these markers to actual clinical response to thiamine: both distinguish populations well, but their distributions overlap so much that neither reliably predicts whether a given child will respond to treatment (Hess, Curr Dev Nutr, 2024). Practical conclusion, also valid in adult medicine: faced with serious clinical suspicion, treat first and discuss later, since thiamine costs almost nothing and presents no risk.

13. Choosing well: B1 alone or B complex?

Vitamin B1 is a case where common sense and science say the same thing: there is almost no reason to take it in isolation. It intervenes in a chain where B2 and B3 ensure the following steps, it needs magnesium to become active, and situations that create B1 deficiency (alcohol, surgery, malnutrition) also create deficiencies in other B vitamins. A few guidelines for choosing:

• The dose : 1 to 10 mg per day cover all nutritional intake scenarios, including athletes. Beyond that, absorption plateaus; doses of 100 mg and above are medication doses.
• The form : thiamine hydrochloride or mononitrate, both are equivalent. Benfotiamine requires a prescription and specific indication, not for routine use.
• The entire B group : verify that B2 and B3 are present, as they are the direct partners of B1 in energy production.
• Magnesium : adequate status determines thiamine effectiveness, and it is often low in stressed, athletic, or alcohol-consuming individuals.
• The promises : "immediate energy," "mosquito repellent," "sugar burner" are unfounded claims. The only authorized claims are energy metabolism, nervous system, psychological functions, and cardiac function.

Frequently asked questions about vitamin B1

Learn More