Thiamine (thiamin, vitamin B1) is a water-soluble B vitamin the body needs to turn food into energy. The body stores very little, so it needs a steady supply from food; as a supplement it is used to cover low intake and in people at risk of deficiency.
Also known as: thiamin, vitamin B1, thiamine mononitrate, thiamine hydrochloride.
ODS lists a Recommended Dietary Allowance of 1.2 mg a day for men and 1.1 mg for women 19 and older (1.4 mg in pregnancy and while breastfeeding). No upper limit has been set. Multivitamins with thiamine typically provide about 1.5 mg; the most common supplement forms are thiamine mononitrate and thiamine hydrochloride.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. ODS says most people in the US get enough thiamine. Groups more likely to fall short include people with alcohol dependence (up to 80% of people with chronic alcoholism develop deficiency), older adults, people with HIV/AIDS or diabetes, and people who have had bariatric surgery; a review found 84 cases of Wernicke's encephalopathy after bariatric surgery between 1991 and 2008.
Deficiency causes beriberi (nerve damage and wasting) and Wernicke-Korsakoff syndrome. Wernicke's encephalopathy is the acute, life-threatening stage; without treatment up to 20% of people with it die. Guidelines cited by ODS recommend thiamine for it preferably into a vein, because even high doses by mouth might not raise blood levels enough.
What studies show: a 2013 Cochrane review found only two trials of thiamine for preventing or treating Wernicke-Korsakoff syndrome in people who misuse alcohol, and concluded the evidence is not enough to guide dose, frequency, route or length of treatment (Day 2013). Per ODS, small studies found 150 to 300 mg a day lowered blood sugar in type 2 diabetes, a meta-analysis of two trials in heart failure found better heart pumping (ejection fraction), and three tiny trials of 3 g a day in Alzheimer's disease were too small to draw conclusions; the clinical meaning of the first two findings was not assessed.
Safety, per ODS: no adverse effects have been reported from high intakes, possibly because absorption falls quickly above 5 mg, so no upper limit was set. The diuretic furosemide is linked to thiamine loss in urine, and the chemotherapy drug fluorouracil has been linked to cases of beriberi and Wernicke's encephalopathy.
We could not find a single published half-life or time to peak for thiamine that applies to a supplement dose, so we do not list one. ODS says thiamine has a short half-life and the body stores only small amounts, mainly in the liver, so people need a continuous supply from food.
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