Thiamin
A B vitamin, also called vitamin B1, that is critical for turning food into energy. The body stores very little, so it needs a steady supply from food.
1.1 mg women
How much you need
The official Recommended Dietary Allowance for adults, per day:
| Age | Men | Women | Pregnancy | Breastfeeding |
|---|---|---|---|---|
| 19–50 years | 1.2 mg | 1.1 mg | 1.4 mg | 1.4 mg |
| 51–70 years | 1.2 mg | 1.1 mg | — | — |
| Over 70 | 1.2 mg | 1.1 mg | — | — |
People aged 18 fall in the official 14–18 group — 1.2 mg a day for males and 1.0 mg for females, and 1.4 mg in pregnancy and when breastfeeding. There is no upper limit at any age. Pregnancy and breastfeeding change what you need — confirm yours with your midwife, obstetrician or doctor.
Upper limit
No upper limit has been set for thiamin, because there are no reports of harm from high intakes (50 mg a day or more) from food or supplements — possibly because absorption falls quickly above 5 mg. The Food and Nutrition Board noted that excessive intakes could still have adverse effects.
What it does
Thiamin, also called vitamin B1, plays a critical role in energy metabolism and so in the growth, development and function of cells [1]. Its main active form, thiamin diphosphate, is an essential cofactor for five enzymes involved in the metabolism of glucose, amino acids and fats [1]. The body holds only about 25 to 30 mg, stored mainly in the liver in very small amounts, and thiamin has a short half-life, so people need a continuous supply from the diet [1].
Forms
Supplements most often contain thiamin mononitrate or thiamin hydrochloride; multivitamins with thiamin typically provide about 1.5 mg [1]. Benfotiamine, a synthetic derivative used in some supplements, is converted to thiamin in the body [1].
Where it comes from
- Breakfast cereals, fortified with 100% of the Daily Value for thiaminfortified1 serving1.2 mg
- Egg noodles, enriched, cookedfortified1 cup0.5 mg
- Pork chop, bone in, broiled3 ounces0.4 mg
- Trout, cooked, dry heat3 ounces0.4 mg
- Black beans, boiled½ cup0.4 mg
How these five were chosen: The five foods with the most thiamin per serving in the NIH fact sheet's food table. Fortified foods are marked.
| Item | Percent of the adult daily amount (1.2 mg) |
|---|---|
| Breakfast cereal | 100% |
| Egg noodles, enriched | 42% |
| Pork chop | 33% |
| Trout | 33% |
| Black beans | 33% |
Getting the most from it
Heat reduces thiamin: bread has 20% to 30% less than its raw ingredients [1]. Because it dissolves in water, much is lost when cooking water is thrown away, and unless white rice is enriched, it has a tenth of the thiamin in brown rice [1]. About half the thiamin in the U.S. diet comes from foods it has been added to [1].
In the United States
Most Americans get enough thiamin: in 2003–2006 data, only 6% had usual intakes below the average requirement [1]. Adults aged 20 and older average 1.95 mg a day from food for men and 1.39 mg for women, and 4.89 mg and 4.90 mg including supplements [1]. Cereals and bread are the most common sources in the U.S. diet, and pork is another major source [1]. There are no current data on how many Americans are deficient [1].
Who is most likely to run low
- People with alcohol dependence — up to 80% of people with chronic alcoholism develop thiamin deficiency, because alcohol reduces its absorption and storage [1]
- Older adults — up to 20% to 30% have laboratory signs of some degree of deficiency [1]
- People with HIV/AIDS [1]
- People with type 1 or type 2 diabetes, whose blood thiamin can be much lower than in healthy people [1]
- People who have had bariatric surgery, after which severe deficiency can lead to beriberi or Wernicke's encephalopathy [1]
What deficiency looks like
Early deficiency can cause weight loss and loss of appetite, confusion, short-term memory loss, muscle weakness and heart symptoms such as an enlarged heart [1]. Its most common effect is beriberi, mainly nerve damage and wasting, which in rare cases causes heart failure; supplemental thiamin cures it quickly [1]. In the United States, deficiency more often shows as Wernicke-Korsakoff syndrome: Wernicke's encephalopathy, which kills up to 20% of those untreated, followed by Korsakoff's psychosis, with severe short-term memory loss, disorientation and confabulation [1]. In about a quarter of people at that chronic stage, treatment does not bring recovery [1].
What the evidence supports, and what it doesn't
Established. Thiamin is essential for energy metabolism, and deficiency causes beriberi and Wernicke-Korsakoff syndrome [1]. Supplemental thiamin quickly cures beriberi [1].
Not supported by trials. Alzheimer's disease: a 2001 Cochrane review of three trials of 3 g a day, each with fewer than 20 patients, could draw no conclusions [1]. Wernicke-Korsakoff syndrome: a 2013 Cochrane review found the trial evidence insufficient to guide the dose, frequency, duration or route of thiamin treatment — although guidelines still treat it with high-dose thiamin, preferably by injection [1].
Mixed. Diabetes: some small studies found that 150 to 300 mg a day lowered blood sugar in people with type 2 diabetes or impaired glucose tolerance, without assessing whether that mattered clinically, and studies of benfotiamine for diabetic nerve and kidney damage have mixed results [1]. Heart failure: a meta-analysis of two small trials found that thiamin improved how well the heart pumped, but its clinical significance was not assessed [1].
Too much
The body excretes excess thiamin in urine, and no harm has been reported from high intakes from food or supplements [1].
Medicines that interact
Thiamin is not known to interact with any medicines, but some medicines lower thiamin [1]. Furosemide (Lasix), a diuretic, increases thiamin loss in urine, possibly to deficient levels [1]. Fluorouracil, a chemotherapy drug, has caused cases of beriberi and Wernicke's encephalopathy [1]. If you take either regularly, talk to your doctor or pharmacist about your thiamin status.
References
- NIH Office of Dietary Supplements. Thiamin — Fact Sheet for Health Professionals. Updated 9 February 2023. ods.od.nih.gov
How we reviewed this page
Every value on this page comes from the NIH Office of Dietary Supplements — Thiamin, Health Professional Fact Sheet, which presents the official U.S. intake recommendations set by the National Academies. The source was last updated on February 9, 2023, and this page was checked against it on October 18, 2026. Numbered markers link to the source for each claim, so you can check the original rather than take our word for it.
Drafted with AI assistance, then edited and fact-checked by a human. No value is published on the strength of a model's recall.
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General information only. This is not medical advice.