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Vitamin B1—Thiamin, the Carbo Burner

Thiamin was first discovered in Japan in the early 1900s, when the lack of thiamin in white rice caused beriberi. Thiamin was first synthesized in 1936. Thiamin is found in rice bran and rice germ, both of which are removed when white riceis made from brown rice. Thiamin plays a key role in the metabolism of energy in all cells. Thiamin is part of the coenzyme ThiaminPyroPhosphate (TPP), which helps convert pyruvate to acetyl-coenzyme A (also known as acetyl-CoA). This is a necessary step in the production of cellular energy from carbohydrates as shown in Figure -3. Magnesium is needed to convert thiamin to TPP. Although refined grains are often fortified with thiamin, their original magnesium is depleted by an average of 76 percent. Magnesium deficiency may also have played a part in beriberi since so much magnesium is lost when white rice is refined.

Thiamin Coenzyme forms are:

ThiaminPyroPhosphate (TPP)

Thiamin Triphosphate (TTP

Thiamin is also found in the form of thiamin triphosphate in nerve and muscle cells. This form of thiamin ctivates the transport of electrolytes across the membranes of nerve and muscle cells. This allows healthy nerve conduction and muscle action.

The amount of dietary thiamin needed is based on the amount needed in producing energy. Thiamin needs will be met by most normal diets if enough food is

Figure -3 The role of thiamin in energy production.

eaten to meet energy requirements. People generally get enough thiamin to meet the Recommended Daily Allowance (RDA), although marginal thiamin deficiency affects about one quarter of the people in the United States and Canada. Elderly people are at risk of thiamin deficiency because of low intakes and reduced

absorption.

The RDA for men is 1.2 mg per day and for women, 1.1 mg.Please see Table 1  for B vitamin RDAs and Adequate  Daily Intakes (AI) for all ages. When enough information cannot be gathered to establish an RDA, an AI is established as a rough guide. Please refer to Table 2 for common supplemental amounts of the B vitamins for adults. These amounts are well above the RDAs, yet still below any established upper intake levels. These amounts may be high enough to compensate for extra stress and food that is depleted of some of its B vitamins.

Thiamin deficiency can result from inadequate food intake. Thiamin deficiency is common among alcoholics, who often have inadequate food intakes. Alcohol provides energy without providing many of the necessary nutrients. Alcohol also impairs the absorption of thiamin, while increasing excretion of thiamin. Enzymes present in raw fish and shellfish destroy thiamin. Also, tannins in tea and coffee can oxidize thiamin, reducing the availability of thiamin in the diet. Extreme thiamin

Table 1 RDAs for the B vitamins are bold and the AIs are not bold.

Table 2 Typical supplement amounts of the B vitamins

Summary for Thiamin—Vitamin B1

Main function: energy metabolism.

RDA: men, 1.2 mg; women, 1.1 mg.

No toxicity reported, no upper intake level set.

Deficiency disease: beriberi.

Healthy food sources: whole grains, and found in most raw or lightly cooked foods.

Degradation: easily destroyed by heat.

Coenzyme forms: ThiaminPyroPhosphate (TPP), Thiamin Triphosphate (TTP).

deficiency can lead to an enlarged heart, weight loss, muscular weakness, poor short-term memory, and cardiac failure. If thiamin is absent or too low in the diet for prolonged periods, this can result in beriberi. Beriberi can result from the consumption of unfortified refined grains such as white flour. Beriberi can cause damage to the nervous system, heart, and muscles.

Milligrams and Micrograms

One gram           = 1000 mg (milligram)

One milligram     = 1000 mcg (microgram)

Some vitamin and mineral amounts are measured in milligrams and some are measured in micrograms.

Thiamin is found in small but sufficient quantities in most nutritious foods, especially whole grains; please refer to Graph 1. Only highly refined foods are lacking in thiamin. Pork products are very high in thiamin. Healthy foods rich in thiamin include soy milk, acorn squash, pistachio nuts, fortified foods, green peas, and watermelon. Thiamin supplements and the thiamin used in food fortification are usually in the form of thiamin hydrochloride or thiamin nitrate. Thiamin is not toxic in food or in the amounts found in most vitamin upplements.

Cooking can reduce thiamin in two ways. Thiamin is destroyed by heat. Also, thiamin is easily leached out of food by water, as seen in Figure 4. To minimize the loss of thiamin and other water-soluble vitamins during cooking, food can be steamed or made into stews and soups.

Figure 4 Thiamin can be lost in cooking

Graph 1 Thiamin amounts in some common foods.

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