Vitamin B1 (Thiamin) Calculator

What is Vitamin B1 (thiamin)?

Vitamin B1, also known as thiamin or thiamine, is a water-soluble vitamin that plays a central role in energy metabolism. As a precursor of thiamin pyrophosphate (TPP), it serves as an essential cofactor for several key enzymes involved in glucose metabolism, including pyruvate dehydrogenase (which converts pyruvate to acetyl-CoA for entry into the Krebs cycle), alpha-ketoglutarate dehydrogenase (a step within the Krebs cycle itself), and transketolase (a key enzyme in the pentose phosphate pathway that generates ribose for nucleic acid synthesis and NADPH for antioxidant defense). Without adequate thiamin, these metabolic pathways slow, leading to impaired energy production and accumulation of metabolic intermediates that can damage tissues.

Thiamin is also critical for nerve conduction. The exact mechanism is not fully understood, but TPP appears to be required for the maintenance of myelin sheaths and for the synthesis of neurotransmitters including acetylcholine. Thiamin deficiency affects the nervous system first, producing the symptoms of beriberi and Wernicke-Korsakoff syndrome.

Recommended daily intake

The Recommended Dietary Allowance (RDA) for thiamin, established by the U.S. National Academies of Sciences, Engineering, and Medicine, varies by age, sex, and life stage:

• Adult men (19+): 1.2 mg/day
• Adult women (19+): 1.1 mg/day
• Pregnancy: 1.4 mg/day
• Lactation: 1.4 mg/day
• Adolescents 14-18: 1.2 mg (M), 1.0 mg (F)

No Tolerable Upper Intake Level (UL) has been established for thiamin because there are no reports of adverse effects from high oral intakes. Thiamin is water-soluble, and excess is rapidly excreted in the urine. However, intravenous thiamin in very high doses can rarely cause allergic reactions.

Food sources of thiamin

Thiamin is found in a wide variety of foods, but the richest sources are:

• Pork: ~0.9 mg per 100 g (one of the richest sources)
• Fortified breakfast cereals: often 1.0-1.5 mg per serving
• Whole grains: brown rice, oats, whole wheat, 0.3-0.5 mg per cup
• Sunflower seeds: ~1.5 mg per 100 g
• Legumes: black beans, lentils, 0.2-0.4 mg per cup cooked
• Yeast extract (Marmite/Vegemite): very high, ~10 mg per 100 g
• Trout and other fish: 0.2-0.4 mg per 100 g
• Nuts (macadamia, pistachio): 0.3-0.7 mg per 100 g

Refined grains (white flour, white rice) lose much of their thiamin during milling, which is why many countries mandate fortification of white flour and refined cereals with thiamin. In the United States, enriched flour contains 0.44 mg of thiamin per 100 g.

Deficiency, beriberi and Wernicke-Korsakoff

Thiamin deficiency produces two classic syndromes. Beriberi occurs in two forms: "wet" beriberi, characterized by cardiovascular symptoms including edema, tachycardia, and right-sided heart failure; and "dry" beriberi, characterized by peripheral neuropathy with symmetric muscle weakness, sensory loss, and diminished reflexes. Beriberi is most common in populations whose diet consists largely of polished white rice without adequate fortification, and in chronic alcohol users.

Wernicke-Korsakoff syndrome is a severe neurological complication of thiamin deficiency most often seen in chronic alcoholics. Wernicke encephalopathy presents acutely with the triad of ataxia, ophthalmoplegia (eye movement paralysis), and confusion. If untreated, it progresses to Korsakoff syndrome, a chronic condition characterized by severe anterograde amnesia, confabulation, and irreversible brain damage. Emergency administration of intravenous thiamin (typically 500 mg IV three times daily for 3-5 days) is essential before any glucose-containing fluids are given, as glucose metabolism consumes thiamin and can precipitate or worsen Wernicke encephalopathy.

Risk factors for deficiency

Several populations are at increased risk of thiamin deficiency:

• Chronic alcohol users: alcohol impairs thiamin absorption and storage
• Bariatric surgery patients: reduced intake and absorption
• HIV/AIDS: increased metabolic demand and reduced intake
• Hyperemesis gravidarum: prolonged vomiting depletes thiamin stores
• Long-term diuretic use: furosemide and other loop diuretics increase thiamin excretion
• Dialysis patients: thiamin is lost in dialysate
• High-carbohydrate diets: thiamin requirement scales with carbohydrate intake
• Older adults: reduced intake, absorption, and storage

Special populations

Pregnancy increases thiamin requirements to 1.4 mg/day due to increased energy metabolism, fetal demand, and urinary losses. Lactating women require the same 1.4 mg/day to support milk production, which contains approximately 0.2 mg of thiamin per liter. Older adults may benefit from thiamin supplementation even when intake appears adequate, as absorption efficiency decreases with age.

Athletes consuming high-carbohydrate diets may have increased thiamin requirements because thiamin is consumed in proportion to glucose metabolism. Some studies suggest that athletes consuming more than 50% of calories from carbohydrate may need 1.5-2.0 mg of thiamin daily. However, the typical Western diet usually provides adequate thiamin for most athletes.

Testing and diagnosis

Thiamin status can be assessed by measuring erythrocyte (red blood cell) transketolase activity and the percentage increase in activity when TPP is added (the "TPP effect"). A TPPE greater than 15-25% suggests thiamin deficiency. Direct measurement of thiamin pyrophosphate in whole blood by high-performance liquid chromatography (HPLC) is more accurate but less commonly available. Clinical diagnosis of Wernicke encephalopathy is made on the basis of clinical presentation, often confirmed by MRI showing characteristic lesions in the mammillary bodies and periaqueductal gray matter.

Supplementation guidance

For most healthy adults consuming a varied diet, thiamin supplementation is unnecessary. Multivitamins typically contain 1.5-3 mg of thiamin, which is well within safe limits. For chronic alcohol users, a daily multivitamin containing thiamin is recommended. For patients with confirmed deficiency or at high risk, oral thiamin supplements of 50-100 mg daily are typically used. In acute Wernicke encephalopathy, intravenous thiamin (500 mg three times daily for 3-5 days) is the standard treatment.

Thiamin is sometimes combined with other B vitamins (B6, B12) in "B-complex" supplements, often marketed for energy. While B vitamins are essential for energy metabolism, supplementation above the RDA does not increase energy levels in adequately nourished individuals, energy is limited by other factors (caloric intake, oxygen delivery, muscle conditioning).

Drug interactions

Loop diuretics (furosemide, bumetanide) increase thiamin excretion and may cause deficiency with long-term use, particularly in heart failure patients. Metformin may reduce thiamin absorption and has been associated with lower thiamin levels in some studies. Fluorouracil (5-FU), a chemotherapy agent, can inhibit thiamin phosphorylation. Chronic alcohol consumption impairs thiamin absorption and storage through multiple mechanisms. Patients on long-term diuretics or metformin should be aware of the potential for thiamin depletion and consider a multivitamin supplement.

Clinical considerations and nuances

Thiamin plays several specific clinical roles that practitioners should know. In the emergency department, any patient with signs of Wernicke encephalopathy (ataxia, ophthalmoplegia, confusion), particularly chronic alcohol users or those with malnutrition, should receive intravenous thiamin (500 mg IV three times daily for 3-5 days) before any glucose-containing fluids. Giving glucose without thiamin can precipitate or worsen Wernicke encephalopathy by exhausting residual thiamin stores during glucose metabolism. This is one of the most important "never events" in emergency medicine.

Heart failure patients on long-term loop diuretic therapy (furosemide, bumetanide, torsemide) are at risk of thiamin deficiency because loop diuretics increase urinary thiamin excretion. Studies have shown that 20-90% of heart failure patients on chronic loop diuretics have biochemical thiamin deficiency, and some small trials have suggested that thiamin supplementation (50-200 mg daily) improves cardiac function in this population. Cardiology guidelines do not yet routinely recommend thiamin supplementation for heart failure patients, but many cardiologists consider it reasonable for patients on high-dose loop diuretics.

Bariatric surgery patients (especially Roux-en-Y gastric bypass) are at high risk of thiamin deficiency due to reduced intake, reduced absorption (the proximal small intestine is bypassed), and frequent vomiting in the early postoperative period. Guidelines recommend a daily multivitamin containing at least 50 mg of thiamin for all bariatric surgery patients, with higher doses (100 mg daily) for those with persistent vomiting. Any bariatric patient with neurologic symptoms, heart failure, or unexplained fatigue should be evaluated for thiamin deficiency and treated empirically if suspected.

Hyperemesis gravidarum (severe nausea and vomiting of pregnancy) can cause thiamin deficiency through prolonged vomiting and reduced intake. Wernicke encephalopathy has been reported in hyperemesis patients, particularly after treatment with IV glucose without thiamin. Pregnant patients with hyperemesis requiring IV fluids should receive thiamin supplementation (100 mg daily) along with other B vitamins.

Clinical considerations and nuances

Choline has several specific clinical applications. In prenatal nutrition, choline has emerged as a critical nutrient for fetal brain development. Animal studies show that maternal choline supplementation improves offspring memory, attention, and information processing speed, with effects that persist into adulthood. Human trials suggest similar benefits, for example, a 2018 randomized trial found that infants of mothers who took 930 mg/day of choline during the third trimester had faster information processing speed at 4 and 13 months compared with those whose mothers took 480 mg/day. The American Medical Association has recommended that all prenatal vitamins include choline, and the 2020-2025 Dietary Guidelines for Americans specifically identify choline as an important nutrient during pregnancy. However, most prenatal vitamins still do not contain choline, and most pregnant women fall short of the 450 mg/day AI.

In non-alcoholic fatty liver disease (NAFLD/MASLD), choline deficiency has been linked to hepatic steatosis because choline is required for VLDL assembly and triglyceride export from the liver. Patients on long-term parenteral nutrition without choline develop fatty liver, which resolves with choline repletion. Some observational studies have linked higher choline intake to lower NAFLD risk, and small trials have tested choline supplementation for NAFLD treatment, with mixed results. Choline is not yet a standard treatment for NAFLD, but ensuring adequate intake is reasonable.

In cognitive aging and dementia, choline (as a precursor for acetylcholine) has been studied as a potential preventive or therapeutic intervention. CDP-choline (citicoline) and alpha-GPC are forms that cross the blood-brain barrier more efficiently and have been studied in animal models of dementia and in human trials of stroke recovery and cognitive decline. Results have been mixed, with some trials showing modest cognitive benefit and others showing no effect. CDP-choline is used in some countries as a prescription medication for stroke recovery and cognitive impairment, but it is not approved for these uses in the U.S.

In sports nutrition, choline has been studied for endurance exercise because prolonged exercise can deplete acetylcholine and theoretically contribute to fatigue. Some studies have shown that choline supplementation (typically as choline citrate or phosphatidylcholine, 1-2 grams before exercise) can prevent the decline in plasma choline during prolonged exercise (marathons, ultramarathons, long cycling events). However, the evidence for performance benefit is inconsistent, and choline is not a standard part of most sports nutrition recommendations.

For people with homocystinuria (a genetic disorder of methionine metabolism) or with high homocysteine from other causes, choline (as betaine) can serve as a methyl donor to convert homocysteine back to methionine, lowering plasma homocysteine. Betaine anhydrous (trimethylglycine) is used clinically for this purpose, often in combination with vitamin B6, folate, and B12. The combination is also sometimes used for elevated homocysteine in cardiovascular risk reduction, though trials have not consistently shown clinical benefit.

Practical takeaways

Vitamin B1 (thiamin) is an essential water-soluble vitamin required for energy metabolism and nerve function. Most adults need 1.1-1.4 mg per day, which is easily obtained from a varied diet that includes whole grains, pork, legumes, and fortified cereals. Deficiency is rare in well-nourished populations but is a real concern for chronic alcohol users, bariatric surgery patients, and those on long-term diuretics. If you fall into a high-risk group, a daily multivitamin containing thiamin is a sensible safeguard. For everyone else, focus on whole grains and minimally processed foods to ensure adequate intake.