Vitamin B1, also called thiamine or thiamin, is one of 8 B vitamins. All B vitamins help the body to convert food (carbohydrates) into fuel (glucose), which is "burned" to produce energy. These B vitamins, often referred to as B complex vitamins, also help the body metabolize fats and protein. B complex vitamins are necessary for healthy skin, hair, eyes, and liver. They also help the nervous system function properly.

All the B vitamins are water-soluble, meaning that the body does not store them.

Like other B complex vitamins, thiamine is considered an "anti-stress" vitamin because it may strengthen the immune system and improve the body's ability to withstand stressful conditions. It is named B1 because it was the first B vitamin discovered.

Thiamine is found in both plants and animals and plays a crucial role in certain metabolic reactions. For example, it is required for the body to form adenosine triphosphate (ATP), which every cell of the body uses for energy.

Thiamine deficiency is rare, but can occur in people who get most of their calories from sugar or alcohol. People with thiamine deficiency have difficulty digesting carbohydrates. As a result, a substance called pyruvic acid builds up in their bloodstream, causing a loss of mental alertness, difficulty breathing, and heart damage (a disease known as beriberi).

Beriberi

The most important use of thiamine is to treat beriberi, which is caused by not getting enough thiamine in your diet. Symptoms include swelling, tingling, or burning sensation in the hands and feet, confusion, difficulty breathing (from fluid in the lungs), and uncontrolled eye movements (called nystagmus). Although people in the developed world generally do not have to worry about getting enough thiamine because foods such as cereals and breads are fortified with the vitamin, people can develop a deficiency fairly quickly, because the body does not store thiamine.

Wernicke-Korsakoff syndrome

Wernicke-Korsakoff syndrome is a brain disorder caused by thiamine deficiency; as with beriberi, it is treated by giving supplemental thiamine. Wernicke-Korsakoff is actually two disorders: Wernicke's disease involves damage to nerves in the central and peripheral nervous systems and is generally caused by malnutrition stemming from habitual alcohol abuse. Korsakoff syndrome is characterized by memory impairment and nerve damage. High doses of thiamine can improve muscle coordination and confusion, but only rarely improves memory loss.

Cataracts

Some preliminary evidence suggests that thiamine -- along with other nutrients -- may lower risk of getting cataracts. People with plenty of protein and vitamins A, B1, B2, and B3 (niacin) in their diet are less likely to develop cataracts. Getting enough vitamins C, E, and B complex (particularly the B1, B2, B9 [folic acid], and B12 [cobalamin) may further protect the lens of your eyes from developing cataracts. More research is needed to be sure.

Alzheimer's disease

Because lack of thiamine can cause dementia in Wernicke-Korsakoff syndrome, it has been proposed that thiamin might help reduce severity of Alzheimer's disease. Scientific studies have not always shown any benefit from thiamin, however. Much more research would be needed before thiamine could be proposed as an effective treatment for Alzheimer's disease.

Heart failure

Thiamine may be related to heart failure in two ways. First, low levels of thiamine can lead to "wet beriberi," a condition where fluid builds up around the heart. However, it isn't clear that taking thiamin will help people with heart failure not related to beriberi.

Many people with heart failure take diuretics (water pills), which help rid the body of excess fluid. But diuretics may also cause the body to get rid of too much thiamin. A few small studies suggest that taking thiamin supplements may help. A multivitamin, taken regularly, should provide enough thiamine.

Most foods contain small amounts of thiamine. Large amounts can be found in pork and organ meats. Other good dietary sources of thiamine include whole-grain or enriched cereals and rice, wheat germ, bran, brewer's yeast, and blackstrap molasses.

Vitamin B1 can be found in multivitamins (including children's chewable and liquid drops), B complex vitamins, or if can be sold individually. It is available in a variety of forms including tablets, softgels, and lozenges. It may also be labeled as thiamine hydrochloride or thiamine mononitrate.

As with all medications and supplements, check with a health care provider before giving vitamin B1 supplements to a child.

Daily recommendations for dietary vitamin B1 are listed below.

Pediatric

• Newborns to 6 months: 0.2 mg (adequate intake)
• Infants 7 months to 1 year: 0.3 mg (adequate intake)
• Children 1 - 3 years: 0.5 mg (RDA)
• Children 4 - 8 years: 0.6 mg (RDA)
• Children 9 - 13 years: 0.9 mg (RDA)
• Males 14 - 18 years: 1.2 mg (RDA)
• Females 14 - 18 years: 1 mg (RDA)

Adult

• Males 19 years and older: 1.2 mg (RDA)
• Females 19 years and older: 1.1 mg (RDA)
• Pregnant females: 1.4 mg (RDA)
• Breastfeeding females: 1.5 mg (RDA)

Doses for conditions like beriberi and Wernicke-Korsakoff syndrome are determined by a doctor. For Wernicke-Korsakoff syndrome, thiamine is given intravenously.

A daily dose of 50 - 100 mg is often taken as a supplement. Thiamine appears safe even at high doses; however, you should talk to your doctor before taking a large amount.

Because of the potential for side effects and interactions with medications, you should take dietary supplements only under the supervision of a knowledgeable health care provider.

Thiamine is generally nontoxic. Very high doses may cause stomach upset.

Taking any one of the B vitamins for a long period of time can result in an imbalance of other important B vitamins. For this reason, you may want to take a B complex vitamin, which includes all the B vitamins.

If you are currently being treated with any of the following medications, you should not use vitamin B1 without first talking to your health care provider.

Digoxin --Laboratory studies suggest that digoxin (a medication used to treat heart conditions) may reduce the ability of heart cells to absorb and use vitamin B1; this may be particularly true when digoxin is combined with furosemide (Lasix, a loop diuretic).

Diuretics -- Diuretics (particularly furosemide, which belongs to a class called loop diuretics) may reduce levels of vitamin B1 in the body. It's possible that other diuretics may have the same effect. If you take a diuretic, ask your doctor if you need a thiamine supplement.

Phenytoin (Dilantin) -- Some evidence suggests that some people taking phenytoin have lower levels of thiamine in their blood, and that may contribute to the side effects of the drug. However, that is not true of all people who take phenytoin. If you take phenytoin, ask your doctor if you need a thiamine supplement.

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