Vitamin B1 (Thiamin)
While Americans are continuing their love affair with vitamins, most people don't think much about thiamin. For many years, the biggest controversy about this vitamin had been how to spell it with an "e" on the end or without. But some of our ancestors weren't so fortunate and succumbed in large numbers to the ravages of beriberi, the traditional name for thiamin deficiency.
Scientists first isolated thiamin in 1926, but centuries before this, the deficiency disease ran rampant throughout the Far East. The earliest mention of what was most certainly thiamin deficiency was in Neiching, a Chinese medical book, dating back to 2697 B.C.E. Beriberi means "I can't, I can't" in Sinhalese and earned its name because of a peculiar head movement associated with the nerve damage accompanying the disease. In a nutrition coup similar to that for vitamin C, a nineteenth-century surgeon in the Japanese navy found that adding meat and whole grains to the usual navy rations dramatically reduced the incidence of beriberi among sailors. Although it's tragic that thousands of sailors died, those long sea voyages were the perfect vehicle for helping scientists to learn about vitamins.
Fifteen years later, a Dutch prison physician discovered a similar connection. Prisoners who were fed polished rice, that had lost most of its thiamin along with the rice bran, developed beriberi. The "scraps" of rice bran, in turn, were used as chicken feed. He noticed that when the chickens ate the same rice as the prisoners, they also developed the disease. More important, he discovered that by feeding the chickens rice bran, the disease was cured.
When it was isolated in the early 1920s, it was named "the B vitamin." Later, nutrition researchers had to assign numbers to the other B vitamins, which they discovered shortly thereafter, and figured out that what was thought to be one nutrient were actually several. Once they named it, it was easy to learn what the vitamin does in the body. The major role of thiamin is as a coenzyme, as are the other B vitamins, that helps release energy from carbohydrate in the foods you eat. Thiamin is also involved in nerve transmission, sitting on the nerve cell membrane, and helps orchestrate nerve impulses and movement in muscles as a result.
The symptoms of thiamin deficiency dramatically show its importance in nerve function, although the specific clinical picture depends on the person's age. Beriberi can either be wet, referring to water retention, or dry, characterized by muscle wasting. Dry beriberi strikes the nervous system and induces spasms and uncontrolled movement, and wet beriberi mostly affects the heart. The deficiency is most common in infants between the ages of two and three months. Thiamin-deficient babies with wet beriberi cry in loud piercing tones, turn blue, vomit, and have trouble breathing. The heart becomes enlarged, and death can follow within hours unless they receive a dose of thiamin. In infants with dry beriberi, crying ranges from hoarseness to no sound at all, and nerve damage shows up as purposeless movement of the hands and arms.
Wet beriberi in adults causes fluid retention, rapid heartbeat, heart enlargement, and eventual congestive heart failure. Adults can also develop a type of beriberi that affects the brain and nervous system, Wernicke-Korsakoff syndrome. Although each of those two words can be two separate disorders, they often appear together, especially in cases of alcohol abuse. The symptoms include mental confusion, unsteady gait, and significant memory dysfunction. Scientists now believe that some people may have a subclinical deficiency, showing no overt signs, only general symptoms such as irritability, headaches, and fatigue.
How Much Do We Need?
The new DRI for thiamin is lower than the 1989 RDA at 1.2 mg for men and 1.1 mg for women. Because of its role in energy metabolism, the requirement is based on caloric intake. So the more calories you take in, the more thiamin you need as well, and this is true for all B vitamins that help process energy. Although it's widely distributed in the food supply through grain products, excellent sources include organ meats, pork, brewer's yeast, and whole grains. Thiamin is one of the safest vitamins, with no reports of side effects even at high doses of 500 mg daily over a month-long period.
Like other B vitamins, thiamin is lost in the flour milling process as the outer covering and bran are removed. To combat nutrient deficiencies, several decades ago the government passed legislation, the Flour Enrichment Act, mandating the addition of thiamin, riboflavin, niacin, and iron to flour. So the term enriched grain products refers to cereals and baked goods made from flour that has this added quartet of nutrients. Of course, if you eat the whole grain product, you get the added bonus of bran and the germ inside the grain head. The germ contains even more vitamins and minerals and, of special interest, fat soluble nutrients such as vitamin E.
Some other ways of losing thiamin include the practice of adding sodium bicarbonate, baking soda, to green beans and peas to keep the pretty green color during cooking, and to dried beans and peas to soften their skins. The baking soda inactivates the thiamin, so it no longer can carry out its functions in the body. High cooking temperatures also destroy the vitamin, with temperatures used to cook meats, vegetables, and grain products causing losses of up to 50 percent. Just like its other water soluble relatives, thiamin will be lost in cooking water that you pour down the drain. One storage technique that doesn't affect this sensitive vitamin is freezing.
Several compounds that occur naturally in foods can interfere with thiamin, and they're important enough to have earned a name for this action: antithiamin factors (ATF). Some of the foods that contain ATF include freshwater fish guts, shellfish, ferns, tea, and some vegetables. Scientists have reported cases of thiamin deficiency caused by excessive intake of tea and coffee in combination with a diet that's not high in thiamin to start with. The minerals calcium and magnesium interact with tannin compounds in tea, coffee, nuts, and wine to compound the thiamin interference. But there are some helpers as well, with vitamin C boosting thiamin status and the acid in fruits and vegetables protecting against the action of the minerals.
Chronic alcoholics are likely to become deficient for several reasons. One obvious reason relates to the poor diet that is typical in chronic alcoholism. Other factors are more complex and involve various aspects of thiamin absorption, which is decreased in alcoholism, and thiamin metabolism. The vitamin is necessary for alcohol metabolism, and with excessive alcohol ingestion, this takes precedence over other metabolic functions in which thiamin is involved.
Some other groups may also be at risk for thiamin deficiency. Surveys of vitamin intake in the United States show that the average woman's intake barely met the previous RDA. And breast-fed babies whose mothers are thiamin deficient are also at risk for beriberi. At the other end of the age spectrum, the elderly may be vulnerable as well. They often rely on highly processed foods which are easy to prepare, but because thiamin is easily destroyed by processing heat, their intake of the vitamin may be lower than they need. Any condition that increases the need for thiamin can cause a defiCiency, especially if intake is less than ideal. Some of these include strenuous physical activity, pregnancy and lactation, fever, and even adolescence.
One special situation is people who may have a moderate deficiency (not enough for dramatic symptoms) and eat a high-carbohydrate diet. Human studies from the 1940s showed that when moderately deficient subjects were given a dose of glucose, blood levels oflactic and pyruvic acids went up. High levels of these compounds mean that the body is not converting carbohydrate to energy as efficiently as it should.
In a similar vein, other studies reported that glucose loading increased liver and heart glycogen levels, the storage form of carbohydrate. Research has shown that carbohydrate loading can precipitate thiamin-induced nerve damage, and physical activity of as little as one minute of exercise after glucose loading increases pyruvic and lactic acids in thiamin-depleted subjects. This may be of practical concern to athletes who do the popular carbohydrate loading before an event and may not be getting quite enough thiamin in their diets.
Most, Americans get enough thiamin, thanks mostly to the Flour Enrichment Act, but both intake surveys and clinical trials have shown that some people are vulnerable to a deficiency of this important nutrient. Thiamin may have been the first B vitamin discovered, but this vitamin's story is continuing. And for the spelling enthusiasts, the accepted American spelling is without an "e" on the end. Following are a few highlights of recent thiamin research.