Thiamin

Thiamin, also called vitamin B1, is a water-soluble vitamin the body uses to turn carbohydrates into usable energy and to keep nerve cells functioning normally. It cannot be stored in meaningful amounts, so a steady dietary supply matters. Whole and enriched grains, pork, legumes, and seeds are the most reliable everyday sources.

What is thiamin

Thiamin functions as a cofactor for enzymes in carbohydrate metabolism, most importantly the enzyme that converts pyruvate into usable cellular energy, and it plays a supporting role in nerve signal transmission and muscle contraction. Because the body's thiamin stores are small and turn over quickly — MedlinePlus notes deficiency can develop within weeks of inadequate intake — regular dietary intake matters more for thiamin than for fat-soluble vitamins the body can bank for later. MedlinePlus lists whole grains and enriched grain products, wheat germ, pork, fish, eggs, legumes, and seeds as the main food sources. In this project's own data, the most concentrated non-fortified sources by measured amount include baker's yeast, toasted wheat germ cereal, and flaxseed, alongside enriched grain products such as enriched corn masa flour.

Health benefits of thiamin

• Carbohydrate metabolism and nerve function. Thiamin's core, well-established role is enabling the enzymatic steps that convert dietary carbohydrate into energy the brain and nervous system can use; MedlinePlus ties inadequate thiamin directly to nerve damage, muscle weakness, and confusion, which is the practical evidence for why this function matters rather than a claim of a performance or cognitive "boost" in people who are already replete.
• Because thiamin has no other well-documented independent health benefit beyond correcting or preventing deficiency, this page does not list additional claims (e.g., for cardiovascular disease or cancer prevention) — none were found on the trusted-source allowlist, and inventing one would violate this page's sourcing standard.

How much you need

The NIH Office of Dietary Supplements sets the RDA for thiamin at 1.2 mg/day for adult men and 1.1 mg/day for adult women, rising to 1.4 mg/day during both pregnancy and lactation (figures corroborated via WebSearch against the ODS Thiamin Health Professional Fact Sheet, which blocks automated fetching — see Sourcing notes). No Tolerable Upper Intake Level (UL) has been established for thiamin: the Food and Nutrition Board found no reports of adverse effects even at intakes of 50 mg/day or more from food or supplements, and hypothesizes this is because intestinal absorption of thiamin drops sharply above about 5 mg in a single dose. These figures are not yet populated in this project's nutrient_rda table.

Signs of deficiency and excess

Early thiamin deficiency presents as fatigue, irritability, poor appetite, and mild confusion; MedlinePlus describes progression to weakness, more severe confusion, and nerve damage as deficiency continues. The classic, severe deficiency disease is beriberi, which can affect the cardiovascular system (wet beriberi, with swelling and heart strain) or the peripheral nerves (dry beriberi, with numbness, muscle wasting, and difficulty walking). A distinct, more acute form of severe deficiency is Wernicke encephalopathy, which can progress to the largely irreversible Korsakoff syndrome; MedlinePlus' entry on Wernicke-Korsakoff syndrome describes confusion, loss of muscle coordination, and abnormal eye movements in the acute phase, followed by severe, often permanent memory loss and confabulation if the amnestic Korsakoff phase develops. No excess or toxicity signs are documented for thiamin — consistent with the absence of an established UL described above.

Warnings & interactions

Thiamin deficiency risk is concentrated in a few well-documented groups rather than the general population. Chronic, heavy alcohol use is the most common cause in the U.S. because alcohol impairs both thiamin absorption and its storage in the liver; MedlinePlus's Wernicke-Korsakoff entry also names malabsorption disorders, bariatric/weight-loss surgery, severe pregnancy-related nausea (hyperemesis gravidarum), prolonged intravenous nutrition given without thiamin supplementation, and long-term diuretic therapy for heart failure as additional risk factors, since diuretics can increase thiamin loss through urine. Anyone in these groups, or anyone recovering from bariatric surgery specifically, is a candidate for clinical thiamin monitoring rather than self-directed supplementation. No drug interactions or upper-limit toxicity concerns are documented for thiamin from food or standard supplement doses.

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