Quick answer

Thiamine, or vitamin B1, is a B vitamin your body needs to turn food into energy. Adults need 1.1 to 1.2 mg a day, and most Americans get that from fortified grains, pork, fish and beans. The body keeps only a small store, and no harm has been reported from high intakes.^1,2

Key facts

Only about 6% of people in the United States take in less thiamin than the average requirement.²
Above about 5 mg a day the gut absorbs a smaller share, and the body passes the extra in urine.^2,3
Pork, fortified cereals and breads, beans and fish are among the best food sources.^1,2
Furosemide, a diuretic, and fluorouracil, a chemotherapy medicine, can lower thiamin levels.¹

What thiamine does

Thiamin is one of the water-soluble B vitamins. Thiamin and thiamine are two spellings of the same nutrient, also known as vitamin B1. It occurs naturally in some foods, is added to others and is sold as a supplement.²

In the body, thiamin becomes thiamin diphosphate, which five enzymes need to break down sugars, amino acids and fats.²

Those enzymes sit at the center of how cells draw energy from carbohydrate, protein and fat, and the need for thiamin rises when a diet is richer in carbohydrate. Because the vitamin dissolves in water and the body holds so little of it, a regular supply matters.^2,3,4

An adult body holds only about 25 to 30 mg of thiamin, about 80% of it as thiamin diphosphate.^2,3

What the evidence shows

The three statements below are functions European regulators accepted for thiamin after a scientific review by EFSA. They are graded moderate because they describe what the vitamin does in a body that gets enough, not an added effect from taking more. In the EU, a food may carry them only if it is at least a source of thiamin.⁵

Contributes to normal energy-yielding metabolism*^1,2,5

Moderate evidence

Thiamin is needed by the enzymes that release energy from food: as thiamin diphosphate, it is a cofactor for five enzymes that break down sugars, amino acids and fats. 'Contributes to normal energy-yielding metabolism' is the wording European regulators permit for thiamin after EFSA review. It does not mean extra thiamin gives more energy to someone who already gets enough.

Amount studied: Recommended intake: 1.2 mg a day for men and 1.1 mg for women, from all sources

Contributes to normal functioning of the nervous system*^3,5

Moderate evidence

A long-established role of the vitamin, included in the EU list of permitted nutrient-function statements after EFSA review. EFSA explains that the brain and nerves depend on thiamin diphosphate, because enzymes that need it help make the chemical messengers acetylcholine and GABA. It does not mean extra thiamin changes how the brain or nerves work in people who already get enough.

Amount studied: Recommended daily intake from food and supplements

Contributes to normal function of the heart*^3,5

Moderate evidence

Included in the EU list of permitted nutrient-function statements after EFSA review. EFSA reports that the heart is among the organs holding most of the body's thiamin, and that heart tissue has some of the highest levels of its active form. It does not mean extra thiamin changes how the heart works in people who already get enough.

Amount studied: Recommended daily intake from food and supplements

Each statement rests on the recommended daily intake, which most people in the United States already reach through food.²

How much you need

Men need 1.2 mg of thiamin a day from all sources.^1,2

Women need 1.1 mg a day, and 1.4 mg during pregnancy and while breastfeeding.^1,2

Labels use a Daily Value of 1.2 mg, so a product with 100% of the Daily Value covers the amount set for men. The dosage guide lists the amounts for children and teens, the European approach and what people actually eat.²

Where to get it

Whole grains, fortified bread, cereal, pasta and rice, meat (especially pork), fish, legumes such as black beans and soybeans, seeds and nuts all provide thiamin.¹

A serving of breakfast cereal fortified with 100% of the Daily Value has 1.2 mg. A cup of enriched egg noodles has 0.5 mg, and a 3 ounce pork chop, 3 ounces of trout or half a cup of black beans each have about 0.4 mg.²

Breads and cereals are the most common sources in the US diet, largely because so many are fortified, and pork is another major one. Dairy foods and most fruit contain little.²

Forms in supplements

The forms most used in supplements are thiamin mononitrate and thiamin hydrochloride, which are stable and dissolve in water.^1,2

Benfotiamine is a synthetic form of thiamin used in some supplements. It does not dissolve in water and is converted to thiamin in the body.^1,2

In a crossover trial in 24 healthy men, a multivitamin made with fursultiamine, a fat-soluble thiamin derivative, gave more than three times the blood thiamin of one made with thiamin nitrate. A second trial found fursultiamine and benfotiamine about the same.⁶

Multivitamins that contain thiamin typically provide about 1.5 mg, and sometimes more.²

What's in ours

What’s in ours

Men's Multi: Vitamin B1, 7 mg per serving, from the label

The amount in our multivitamin is several times the recommended daily intake behind the statements above. It is also above the level where the gut starts to absorb a smaller share, and no upper limit applies to thiamin.^2,3

Who is more likely to run low

Thiamin deficiency is rare in the United States, but NIH lists groups more likely to run low: people with alcohol dependence, older adults, people with HIV/AIDS, people with diabetes and people who have had bariatric surgery.^1,2

Alcohol appears to be the most common cause in wealthy countries. Up to 80% of people with chronic alcoholism develop thiamin deficiency, because alcohol cuts absorption, liver stores and the body's use of the vitamin.²

For people at high risk, such as heavy drinkers with confusion or unsteady walking, NIH notes that thiamin by mouth may not raise blood levels enough, and guidelines call for injections given by a clinician. That needs urgent medical care, not a supplement.²

Side effects, medicines, and who should ask first

NIH reports no adverse effects from high thiamin intakes of 50 mg a day or more from food or supplements, although experts note that very large intakes could still have effects.^1,2

No upper limit has been set for thiamin, because no harm has been reported from high intakes. Absorption falls above about 5 mg a day, and what the body does not need leaves in urine.^2,3

Thiamin given by injection can rarely cause a serious allergic reaction (anaphylaxis), most often after repeated injections, and deaths have been reported. Warmth, itching, hives, weakness, sweating and nausea have also been reported.⁴

Your doctor may want to check on you

Furosemide, a loop diuretic, has been linked in research to lower thiamin levels, possibly low enough to be deficient, because more thiamin is lost in urine. NIH says people who take it regularly should discuss their thiamin status with their health care providers.^1,2,7

Reported in studies

Your doctor may want to check on you

Fluorouracil, a chemotherapy medicine, has been linked in published cases to severe thiamin deficiency, including beriberi and Wernicke's encephalopathy, possibly because it speeds up thiamin breakdown and blocks its active form. NIH notes that thiamin supplements might reverse some of these effects; that is a decision for the cancer care team.^1,2

Reported in studies

Do not take thiamin if you have had an allergic reaction to it, including to an injection⁴
Ask first if you take furosemide or another loop diuretic, or are having chemotherapy with fluorouracil
Ask first if you drink heavily, have had bariatric surgery, or have diabetes, HIV/AIDS or heart failure
Ask first if you are pregnant and vomiting often, or if you are breastfeeding

Questions people ask

Is thiamine the same as vitamin B1?

Yes. Thiamin and thiamine are two spellings of vitamin B1. Supplement labels usually name the form, most often thiamine mononitrate or thiamine hydrochloride.²

Does thiamine give you more energy?

Thiamin is needed to release energy from food, and most people already get enough from their diet. The graded statements above describe that normal role. None of the sources we use shows extra thiamin adding energy for people who are not short of it.²

Can you take too much thiamine?

From food and tablets, no harm has been reported, even at 50 mg a day or more, and no upper limit is set. The gut absorbs less as the dose rises, and the body passes the excess in urine. Injected thiamin is different: rare serious allergic reactions have been reported.^2,4

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Sources

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.