Vitamin B1 – Thiamine

Vitamin B1, also known as thiamine, is a water-soluble vitamin with a special place in nutrition history: research into beriberi, the disease caused by its deficiency, gave rise to the very idea of vitamins, and in 1926 the anti-beriberi factor became the first vitamin ever isolated in pure form. It is essential for converting food into energy and for normal nerve function, including the health of the myelin sheaths that insulate nerve fibers. Unlike vitamin B12, which the liver can store for years, thiamine is held in only small amounts — roughly 25-30mg in an adult, with a biological half-life of about 9-18 days — so signs of depletion can appear within two to three weeks of inadequate intake. A steady daily supply from food or supplementation is therefore essential.

Vitamin B1 – Key Mechanisms

Vitamin B1’s biological activity depends on its conversion in the cell to thiamine pyrophosphate (TPP) — also called thiamine diphosphate (TDP) — the active coenzyme form. This conversion requires magnesium and ATP. TPP is an essential cofactor for five human enzymes: the four below, which drive energy and amino acid metabolism, plus 2-hydroxyacyl-CoA lyase, which breaks down certain fatty acids (such as phytanic acid) inside peroxisomes.

Pyruvate dehydrogenase complex (PDC): the most important thiamine-dependent step in energy metabolism. This enzyme complex sits at the gateway between glycolysis and the TCA (Krebs) cycle, converting pyruvate to acetyl-CoA. Without functional PDC — which requires TPP — pyruvate can’t be turned into acetyl-CoA efficiently and is diverted to lactate instead, which is why severe deficiency causes lactic acidosis. This bottleneck explains why vitamin B1 deficiency causes such profound energy failure even when carbohydrate intake is adequate: the fuel is present but the gate is locked.

Alpha-ketoglutarate dehydrogenase: a second TPP-dependent step within the TCA cycle itself, converting alpha-ketoglutarate to succinyl-CoA. When this fails, the cycle cannot complete its revolutions regardless of acetyl-CoA availability, further compromising aerobic energy production.

Transketolase: a key enzyme in the non-oxidative branch of the pentose phosphate pathway. It reshuffles sugar molecules to supply ribose-5-phosphate — the starting material for the sugars in RNA and DNA — and recycles sugars back into the pathway’s NADPH-producing branch (NADPH is used for antioxidant defense and fatty acid synthesis). Vitamin B1 deficiency can therefore impair cell replication and antioxidant capacity. Transketolase activity in red blood cells is also the classic lab test for thiamine status.

Branched-chain alpha-keto acid dehydrogenase (BCKDH): involved in the breakdown of the branched-chain amino acids — leucine, isoleucine, and valine — the most abundant essential amino acids in muscle, making up roughly 35% of the essential amino acids in muscle protein.

Thiamine may also have roles in nerve tissue beyond its coenzyme functions. A minor form, thiamine triphosphate, is found in nerve and muscle tissue and can activate certain ion channels in lab studies, but its role in the human body is still unknown. What is well established is that prolonged deficiency can permanently damage nerves and the brain — which is why some neurological symptoms don’t fully resolve even after thiamine is restored.

Vitamin B1 – RDA (Recommended Dietary Allowance)

* Adequate Intake (AI) for infants. Source: US National Academies, via the NIH Office of Dietary Supplements. The daily value used on food labels is 1.2mg.

Vitamin B1 – ODA (Optimal Daily Allowance)

1.5-3mg/day for most adults. People with high carbohydrate intake, heavy exercise loads, or alcohol use sit toward or above the higher end.

The ODA isn’t an official reference value. The reasoning behind it: thiamine needs scale with energy intake — EU reference values set adult intake at 0.4mg per 1,000 kcal — so a 4,000 kcal training diet calls for about 1.6mg/day, and the rest of the range adds a margin. There’s no evidence that intakes beyond this improve health or performance in people who aren’t deficient.

Vitamin B1 is Found In (per 100g)

* Value from USDA’s SR Legacy data, where the Foundation Foods entry doesn’t include it.

Pork is the standout animal source: loin cuts in USDA data range from about 0.5 to 1.0mg per 100g, compared with roughly 0.05-0.15mg for chicken breast and beef and 0.03-0.35mg for most fish. Among plant foods, seeds and nuts lead per 100g; legumes and whole grains contain less per 100g but are usually eaten in bigger portions. Fortified cereals and nutritional yeast can contain very high amounts but vary by product — check the label.

Anti-thiamine factors: several foods contain compounds that actively destroy or block thiamine — a genuinely underknown dietary consideration:

• Thiaminase enzymes are found in some raw fish and shellfish — notably carp and related species, some herring and smelt, and certain clams and mussels — as well as bracken fern, horsetail, and some bacteria. Thiaminase breaks the thiamine molecule apart before it can be absorbed. Cooking inactivates it, so cooked fish and shellfish aren’t a concern, and many fish don’t contain it at all. The clearest human evidence comes from 1970s studies in northeastern Thailand, where villagers who regularly ate raw fermented fish had poorer thiamine status that improved when the fish was cooked. There’s no evidence that occasional sushi or sashimi in a varied diet causes problems.
• Polyphenols such as the tannins in tea — and related compounds in coffee — can bind and inactivate thiamine, and unlike thiaminase they survive heat. The evidence comes from a handful of mostly older studies: in rural northern Thailand, drinking tea or chewing fermented tea leaves worsened thiamine status, and a US study found lower blood thiamine during a period of regular tea drinking. These effects were seen mainly where intake was already marginal. Vitamin C blocks the reaction in lab studies, and there’s no evidence that normal tea or coffee intake causes deficiency in people who eat enough thiamine.
• Betel nut, chewed in parts of South and Southeast Asia, contains heat-stable polyphenol anti-thiamine compounds rather than thiaminase. In the Thai studies, 10mg of supplemental thiamine a day offset the effect of raw fermented fish but not of betel nut chewing.

Vitamin B1 Helps With

• Converting carbohydrates into usable energy — the gateway step from glucose into aerobic metabolism
• Supporting healthy nerve and muscle function, including the heart muscle
• Helping maintain healthy nerve fibers, including their myelin sheaths
• Facilitating TCA cycle energy production through multiple enzyme steps
• Supporting DNA and RNA synthesis via the pentose phosphate pathway
• Breaking down branched-chain amino acids
• Neurotransmitter synthesis — acetylcholine is made from acetyl-CoA, which neurons produce mainly through the TPP-dependent pyruvate dehydrogenase step

Vitamin B1 – For Athletes and Active People

Vitamin B1 requirements rise with energy intake — especially carbohydrate, since all glucose burned aerobically passes through the TPP-dependent pyruvate dehydrogenase step. That’s why EU reference values are expressed per 1,000 kcal: an athlete eating 4,000 kcal a day needs roughly 1.6mg. Whether training raises needs beyond what the extra food supplies hasn’t been firmly established.

The bigger practical risk is a high-calorie diet that’s low in thiamine — or cutting calories to make weight. Whether refined carbohydrates are a problem depends on where you live. Where white flour is routinely enriched (as in the US, Canada and the UK), white bread can contain more thiamine than wholemeal: about 0.48mg versus 0.28mg per 100g in USDA data. Where flour isn’t enriched, milling strips out most of the thiamine, and athletes fueling mainly on white bread, pasta, rice and sugar can fall short.

Pyruvate dehydrogenase is the main gateway for carbohydrate into aerobic metabolism. In genuine deficiency this step slows, more pyruvate is diverted to lactate, and aerobic ATP production suffers. Whether a marginal shortfall affects performance is less clear. In a Dutch study, eight weeks of restricting thiamine together with riboflavin, B6 and vitamin C lowered VO2max by about 10% and the onset of blood lactate accumulation by about 20% — but a follow-up study couldn’t attribute the decline to any single vitamin, and an earlier controlled study that induced thiamine deficiency on its own found no effect on performance.

Supplementing athletes who aren’t deficient hasn’t shown clear benefits either. Two small studies of fat-soluble thiamine derivatives (one in six trained cyclists) found no change in exercise performance, while one small study reported lower lactate and perceived exertion with thiamine supplementation. Getting enough matters; taking more than enough hasn’t been shown to help.

Vitamin B1 is also lost in sweat, though in small amounts — older measurements put it at roughly 10µg per 100ml of sweat. That’s negligible for typical training, but sweating up to 10 liters a day in the heat could add up to about 1mg — enough to matter if intake is already borderline.

During prolonged endurance exercise, the body oxidizes more branched-chain amino acids for fuel, a step that runs through the TPP-dependent BCKDH complex. These amino acids supply only a small share of total energy, though, and there’s no evidence that extra thiamine changes this in people who aren’t deficient.

Benfotiamine is often marketed for nerve health and recovery, but the evidence is weaker than its reputation. Despite the common description, it isn’t truly fat-soluble, and in mice it raised thiamine levels in blood and liver but not in the brain. Short trials (3-6 weeks) in diabetic neuropathy reported modest symptom improvements, while longer trials — 24 months in type 1 diabetes and 12 months in type 2 — found no effect on nerve function. No studies have tested it for nerve injuries in athletes.

Vitamin B1 – Insufficient Doses

Deficiency risk is higher in:

• People with chronic heavy alcohol use — alcohol impairs vitamin B1 absorption, disrupts its conversion to TPP, and is often accompanied by inadequate dietary intake. This is the most common cause of severe vitamin B1 deficiency in high-income countries.
• People eating diets based primarily on polished white rice without fortification — the vitamin B1 in rice is concentrated in the bran and germ, which are removed during polishing. This drove the beriberi epidemics in Asia in the late 1800s and early 1900s, after mechanized milling made polished rice widespread, and it still causes infantile beriberi in parts of South and Southeast Asia today.
• People with malabsorption or persistent vomiting — Crohn’s disease, coeliac disease, after bariatric surgery, or severe pregnancy sickness (hyperemesis gravidarum)
• People on long-term dialysis — vitamin B1 is water-soluble and cleared during treatment
• Those on prolonged IV nutrition without vitamin B1 supplementation
• People who regularly eat raw fermented fish or chew betel nut, particularly when thiamine intake is already low
• People with HIV/AIDS
• Older adults, who more often have low blood thiamine levels
• People with diabetes, who often have low blood thiamine levels
• People eating high-carbohydrate diets built on unfortified refined grains, sugar, or alcohol rather than whole-food vitamin B1 sources

Deficiency conditions:

Wet beriberi: the cardiovascular form. Peripheral blood vessels dilate abnormally, causing the heart to pump harder to maintain perfusion — eventually leading to high-output cardiac failure, peripheral edema, and breathlessness. Can progress to death without treatment.

Dry beriberi: the neurological form. Peripheral neuropathy beginning in the legs (tingling, numbness, burning), ascending muscle weakness, foot drop, wrist drop, and eventually muscle atrophy. Named “dry” because edema is absent.

Infantile beriberi: occurs in breastfed infants, usually in the first six months of life, whose mothers are thiamine-deficient. The acute cardiac form can kill within hours if untreated, but it typically responds dramatically to injected thiamine.

Wernicke-Korsakoff syndrome: the most severe and medically urgent deficiency presentation. It is most often linked to chronic heavy alcohol use, but also occurs with malnutrition, persistent vomiting (including hyperemesis gravidarum), after bariatric surgery, and in serious illness such as cancer or sepsis. Wernicke’s encephalopathy is the acute phase, classically a triad of confusion, ataxia (unsteady gait), and ophthalmoplegia (abnormal eye movements) — but only around 16% of patients show all three, so it is often missed. It is a medical emergency treated with high-dose injected vitamin B1. Without prompt, adequate treatment it frequently progresses to Korsakoff syndrome (historically called Korsakoff’s psychosis): severe amnesia — particularly inability to form new memories — confabulation (unconsciously fabricating memories to fill gaps), and personality changes that may be permanent.

A note on history: in the 1890s, Christiaan Eijkman, a Dutch physician working in Java, found that chickens fed polished rice developed a beriberi-like nerve disease that rice bran prevented. He first thought the bran neutralized a toxin; his successor Gerrit Grijns correctly concluded that polishing removed an essential nutrient. Eijkman shared the 1929 Nobel Prize in Physiology or Medicine for this work. In 1912, Casimir Funk, believing he had isolated the protective substance, coined the term “vitamine” — a vital amine — later shortened to “vitamin” when it became clear that not all vitamins are amines. Funk’s extract turned out to be mostly nicotinic acid (niacin); the anti-beriberi factor itself was first isolated in pure form in 1926 by Barend Jansen and Willem Donath, making thiamine the first vitamin ever isolated. Robert Williams worked out its structure and synthesized it in 1936.

General symptoms of deficiency (earlier stages):

• Fatigue and low energy
• Loss of appetite
• Irritability and poor concentration
• Muscle weakness
• Tingling or numbness beginning in the feet and hands
• Impaired reflexes

Vitamin B1 – Excessive Doses

No Tolerable Upper Intake Level has been established for vitamin B1, because no adverse effects have been reported from high intakes from food or oral supplements. Absorption becomes less efficient at high doses, and the excess is excreted in urine. Trials in Alzheimer’s disease that gave 3g a day orally — around 2,500 times the RDA — reported no significant side effects.

Injected thiamine is different: rare allergic reactions, including anaphylaxis, have been reported with intravenous or intramuscular use. In a study of nearly 1,000 patients given 100mg intravenously, about 1% had minor, mostly local reactions and one person (0.1%) had generalized itching. This is a concern for clinical injections, not oral supplements.

Different Types of Vitamin B1

• Thiamine Hydrochloride — the standard supplemental and injectable form; water-soluble, widely available, and well-studied. Oral thiamine hydrochloride is commonly used for prevention in lower-risk heavy drinkers; anyone with suspected Wernicke’s needs injections.
• Thiamine Mononitrate — absorbs less moisture and is more stable than the hydrochloride in dry products, which is why it’s the usual choice for fortified flour and cereals and is common in multivitamins. Once dissolved, both forms deliver the same thiamine.
• Benfotiamine — a synthetic thiamine derivative that is converted to thiamine after absorption. Often described as fat-soluble, but lab testing shows it is only sparingly soluble in water and doesn’t dissolve in oils; it is converted in the gut into a form that is easily absorbed. It raises blood thiamine levels considerably more than thiamine hydrochloride, but in animal studies it didn’t raise thiamine levels in the brain. It is the most studied form for diabetic neuropathy, with mixed results: short trials suggest modest symptom relief, while longer trials found no effect on nerve function.
• Sulbutiamine — a synthetic, fat-soluble disulfide derivative (two modified thiamine molecules joined together) that, unlike benfotiamine, does raise thiamine levels in the brain. It has been used in France to treat weakness and fatigue and is marketed elsewhere as a nootropic. The evidence is thin: the largest controlled trial (326 people with post-infection fatigue, 28 days) found no overall benefit over placebo, and positive reports come mainly from uncontrolled studies.
• Fursultiamine (TTFD) and related allithiamine-type compounds — fat-soluble disulfide derivatives developed in Japan and sold as supplements. They are well absorbed, but human research is limited, and small studies in athletes found no performance benefit.

Which form for your goal:

Vitamin B1 – How to Take It

Vitamin B1 can be taken at any time of day, with or without food. Because the body holds only small amounts, consistent daily intake matters more than precise timing.

For general maintenance, 1.5-3mg/day (the ODA above) is plenty, and a multivitamin or B complex usually covers it. Many single-ingredient B1 supplements contain 50-100mg — far more than needed, but no adverse effects have been reported at these doses. Benfotiamine doses used in diabetic neuropathy trials are 300-600mg/day, and it was well tolerated in trials lasting a year or more; note that the absence of an upper limit applies to thiamine itself, not automatically to synthetic derivatives. Wernicke’s prevention and treatment is a medical matter: suspected cases are treated with high-dose injected thiamine (European guidelines recommend at least 200mg three times a day).

Daily intake from food is sufficient for most people eating a varied diet that includes whole grains, pork, legumes, nuts, and seeds. If the diet relies heavily on white rice, unfortified refined carbohydrates, or alcohol, supplementation is worth considering.

Vitamin B1 – Interactions

Alcohol is the most significant thiamine antagonist — it reduces absorption in the small intestine, impairs storage and conversion to TPP, and is frequently associated with low dietary vitamin B1 intake. Long-term use of loop diuretics such as furosemide increases thiamine loss in urine and has been linked to low thiamine status in people with heart failure. The chemotherapy drug fluorouracil (5-FU) can interfere with the conversion of thiamine to TPP. Thiaminase in some raw fish and shellfish destroys dietary thiamine before absorption.

Antacids may also reduce the thiamine available for absorption: thiamine breaks down faster in alkaline conditions, and in a 1941 lab study, calcium and magnesium carbonate antacids caused appreciable thiamine losses in gastric juice — partly through alkaline breakdown and partly by binding the vitamin. This hasn’t been confirmed in human studies, but if you take antacids regularly, spacing them a couple of hours apart from B1 supplements is a simple precaution.

Vitamin B1 – Synergy

• Works with other B vitamins in energy metabolism — the pyruvate and alpha-ketoglutarate dehydrogenase complexes need four other cofactors alongside TPP: FAD (from B2), NAD+ (from B3), coenzyme A (from B5), and lipoic acid. B6 runs the transamination step that feeds branched-chain amino acids into BCKDH. A B complex covers these together.
• Magnesium is needed both to convert thiamine into TPP and for TPP-dependent enzymes to work, so low magnesium can blunt thiamine’s effects. That is well established in the lab, but clinical evidence is limited: a 2022 trial in patients with alcohol withdrawal found that lactate levels normalized more consistently when magnesium was given alongside thiamine, while a 2023 multicentre trial found oral magnesium added little clinical benefit in alcohol withdrawal (though it also failed to raise blood magnesium levels). Correcting low magnesium is standard practice when treating Wernicke’s.
• Works with B12 and folate in neurological health and myelin maintenance.
• Supports acetylcholine synthesis alongside choline — acetylcholine is made from choline and acetyl-CoA, which TPP helps generate.

Vitamin B1 – Antagonistic Interactions

• Alcohol impairs absorption, storage, and activation of vitamin B1 — the most clinically significant interaction.
• Thiaminase in some raw fish and shellfish breaks down dietary vitamin B1 before absorption; cooking inactivates it.
• Polyphenols in tea (and related compounds in coffee) may reduce vitamin B1 availability with heavy intake — mainly relevant when intake is already low.
• Loop diuretics increase urinary vitamin B1 excretion.
• Fluorouracil (5-FU) chemotherapy can interfere with the conversion of thiamine to TPP.
• Diets high in unfortified refined carbohydrates increase vitamin B1 use without supplying much of it.
• Antacids may reduce the thiamine available for absorption through alkaline breakdown and binding — shown in lab studies, not yet confirmed in people.

Food values: USDA FoodData Central — sunflower seeds, raw (Foundation Foods, FDC ID 2515381, thiamine from SR Legacy); macadamia nuts, raw (Foundation Foods, 2515378, thiamine from SR Legacy); pork loin, lean only, roasted (SR Legacy, 168233); flaxseed, ground (Foundation Foods, 2262075); Atlantic salmon, farmed, cooked (SR Legacy, 175168); 100% whole wheat bread, commercial (Foundation Foods, 2758994); green peas, boiled (SR Legacy, 170420); black beans, cooked (SR Legacy, 173735); brown rice, cooked (SR Legacy, 169704); lentils, cooked (SR Legacy, 172421). White bread comparison: commercial white bread (Foundation Foods, 2758993). RDA values from the US National Academies, via the NIH Office of Dietary Supplements. % Daily Values use the FDA’s current Daily Value of 1.2mg.