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Vitamins, Minerals and Dietary Supplements

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Vitamin B1 (thiamin)

What is vitamin B1? Why do we need it?

Also known as thiamin, vitamin B1 is a water-soluble vitamin. Since it is not stored in body fat, after the body uses what it needs, any excess vitamin B1 is excreted in the urine.

Why do we need it?

Like most of the B vitamins, thiamin plays a variety of roles in the human body. Its most important function is to help the body's cells convert carbohydrates into ATP – the fuel the body runs on. It is also involved in metabolic activities relating to the heart, brain and muscles, and it helps ensure proper nerve cell function.

How much vitamin B1 should I take?

According to the National Academy of Science, the recommended daily allowance (RDA) for thiamin is as follows:

  • Adult men: 1.5 milligrams/day
  • Adult women: 1.1 milligrams/day
  • Children aged 7-10: 1 milligram/day
  • Infants: 0.4 milligrams/day
  • Pregnant/lactating women: 1.6 milligrams/day

What are some good sources of vitamin B1?

Thiamin is found in almost all foods, but the best sources are pork and other lean meats. Other good sources include enriched and fortified cereals, oatmeal, corn, nuts, beans, cauliflower and sunflower seeds.

What can happen if I don't get enough vitamin B1?

Vitamin B1 deficiency can result in edema and abnormal heart rhythm. Severe B1 deficiency (also known as beriberi) is rare in the U.S. but can occur in severely malnourished people, alcoholics, or people on long-term dialysis. Symptoms may include paralysis, loss of balance, loss of feeling in the legs and feet, visual problems and congestive heart failure.

What can happen if I take too much?

To date, no toxic effects have been reported for vitamin B1. Because it is water-soluble and is not stored in the body, the chances of enough B1 building up to toxic levels are highly unlikely. Most people taking multivitamins with high levels of B1 or eating foods rich in amounts of B1 need not worry about toxicity.


  • B vitamins may cut heart disease risk. Harvard Health News April 1998.
  • B vitamins and the heart: what men can learn from women. Harvard Men's Health Watch June 1998.
  • Cheraskin E, Ringsdorf WM, Medford FH, Hicks BS. The "ideal" daily vitamin B1 intake. J Oral Med 1978; 33:77-79.
  • Recommended Dietary Allowances, 10th ed. Washington, D.C.: National Academy Press, 1989.
  • Insel PM. Thiamin: essential for health. Health Line November 1995.
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