Get to Know Vitamin B1

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Get to Know Vitamin B1

This is the second piece in a series on vitamins and minerals, also called micronutrients. In this series, we’ll cover what each micronutrient does, food sources, supplements, and signs of deficiencies and excess.

Let’s take a look vitamin B1, which is part of a complex of other B vitamins. Like most vitamins, B vitamins have a number of different jobs in the body. One of their main roles is to help turn the food that we eat into energy.

What is vitamin B1?

Vitamin B1, also called thiamin or thiamine, is a water-soluble vitamin (meaning, it dissolves in water) that is found naturally in some foods, is added to some foods, and is available as a dietary supplement.

What does vitamin B1 do?

Vitamin B1 plays a key role in energy metabolism, as well as the growth, development, and function of cells. When you consume vitamin B1 from foods or supplements, it’s absorbed in the small intestine. Humans can store small amounts of this vitamin in the liver, but we need to consume vitamin B1 daily to meet the body’s needs, as the amount that can be stored only lasts a few weeks.

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According to the Office of Dietary Supplements (ODS), which is part of the National Institutes of Health, “About 80% of the approximately 25-30 mg of thiamin in the adult human body is in the form of thiamin diphosphate,” which is the main metabolically active form of the vitamin. In addition, the bacteria in the gut makes some vitamin B1, but it’s not known how much they contribute to the role of this vitamin in the body. Thiamin diphosphate is involved in certain enzymes that play a role in the metabolism of glucose, amino acids, and lipids.

What foods have vitamin B1?

Vitamin B1 is found in a variety of foods, so it’s generally easy to get enough of this vitamin from food sources. Whole grains, meats, and fish naturally contain vitamin B1; it’s also added to breads, cereals, and baby formulas. Here are some examples of foods that are good sources of vitamin B1:

  • Fortified breakfast cereals
  • Enriched breads, noodles, and rice
  • Pork
  • Fish
  • Beans and lentils
  • Sunflower seeds
  • Flaxseeds
  • Nuts
  • Yogurt
  • Acorn squash
  • Tofu

Vitamin B1 is found in multivitamin/mineral supplements, B-complex supplements, and in supplements that only contain vitamin B1. The most common form of vitamin B1 in supplements are thiamin mononitrate and thiamin hydrochloride, which are water-soluble forms. Benfotiamine is a synthetic form of the vitamin that’s found in some supplements, as well; this form is not water soluble and is converted to thiamin in the body, says ODS.

How much vitamin B1 you need?

The Recommended Daily Allowance for vitamin B1 is as follows:

  • For men age 19 and older: 1.2 milligrams (mg) daily
  • For women age 19 and older: 1.1 mg daily
  • For pregnancy and lactation: 1.4 mg daily

What are signs of vitamin B1 deficiency?

Most people in the U.S. are able to consume enough vitamin B1 on a daily basis, with only a very small amount of people getting below the recommended daily amount. It’s relatively easy to meet daily needs from food sources alone. For example, one-half cup of cooked enriched rice provides 1.4 mg of vitamin B1, which is more than what most adults need every day.

While vitamin B1 deficiency is rare in the U.S., some people may have trouble meeting their daily needs. A deficiency can result from inadequate intake, decreased absorption in the gut, or increased losses in the urine. People at risk for a vitamin B1 deficiency include:

  • People with alcohol dependency, due to alcohol reducing vitamin B1 absorption
  • People with HIV/AIDS, likely as a result of malnutrition
  • Older adults, due to various factors including chronic disease and reduced absorption
  • People who have had bariatric surgery, due to reduced absorption of the vitamin
  • People with diabetes, due to increased clearance from the kidneys

Signs of vitamin B1 deficiency may include:

  • Loss of appetite
  • Muscle weakness
  • Pain in the limbs
  • Swollen feet or legs
  • Shortness of breath
  • Confusion or memory loss

A severe vitamin B1 deficiency can lead to a disease called beriberi. According to MedlinePlus, there are two forms of beriberi:

  • Wet beriberi, which affects the cardiovascular system
  • Dry beriberi/Wernicke-Korsakoff syndrome, which affects the nervous system

Wernicke-Korsakoff syndrome can occur with alcohol abuse, and may lead to numbness and tingling in the hands and feet, loss of muscle function, confusion, memory loss, and difficulty walking.

Vitamin B1 deficiencies are treated with oral doses of thiamin; for more severe deficiencies, thiamin may be given intravenously or by intramuscular injections for up to several or more weeks.

What are signs of vitamin B1 toxicity?

Because vitamin B1 is water soluble, excess amounts are excreted in the urine. For this reason, there is no established upper limit of vitamin B1, and toxicity is unlikely. However, the Food and Nutrition Board at the Institute of Medicine of the National Academies have noted that “excessive intakes of thiamin could have adverse effects.”

Other things to know about vitamin B1

Some medicines can affect vitamin B1 levels, such as:

  • Furosemide, a diuretic
  • Fluorouracil, a chemotherapy drug

Talk with your health care provider if you are taking either of these drugs; they may recommend a vitamin B1 supplement.

Eating a lot of raw seafood could lead to a vitamin B1 deficiency; this is because raw fish contains an enzyme called thiaminase that breaks down vitamin B1. However, if you are eating other food sources of vitamin B1 and/or taking a dietary supplement that contains this vitamin, the chances of this happening are likely quite low.

Learn more about vitamins and minerals by reading the other pieces in this series:

Get to Know Vitamin A

Get to Know Vitamin B2

Get to Know Vitamin B3

Get to Know Vitamin B5

Get to Know Vitamin B6

Get to Know Vitamin B7

Get to Know Vitamin B9

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES

Amy Campbell, MS, RD, LDN, CDCES on social media

A Registered Dietitian and Certified Diabetes Educator at Good Measures, LLC, where she is a CDE manager for a virtual diabetes program. Campbell is the author of Staying Healthy with Diabetes: Nutrition & Meal Planning, a co-author of 16 Myths of a Diabetic Diet, and has written for  publications including Diabetes Self-Management, Diabetes Spectrum, Clinical Diabetes, the Diabetes Research & Wellness Foundation’s newsletter,, and

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