Thiamin

Daily Value: 1.5 milligrams

Good Food Sources: Rice bran, pork, beef, fresh peas, beans, wheat germ, ham, oranges, enriched pastas, breads, oatmeal and other cereals

It's tucked discreetly into baked goods and cereals. You probably wouldn't know you're getting thiamin unless you read about it on a food label. But thanks to this water-soluble B vitamin, you're able to turn the starches and sugars in your breakfast bowl into energy.

Unlike the United States, many parts of the world still don't fortify cereals with thiamin, also known as vitamin B₁.

Although rice and whole grains--dietary staples throughout the world--naturally contain thiamin, the process of refining them for consumption removes the nutrient. Folks living on little but devitalized rice and grains soon become thiamin-deficient and develop a disease called beriberi, with symptoms such as weakness, heart enlargement and limb swelling that make even walking difficult, says Howerde Sauberlich, Ph.D., professor in the Department of Nutritional Sciences at the University of Alabama in Birmingham. "I've seen cases of this myself where people were having difficulty walking, and almost miraculously, within a few hours after being given thiamin, they could walk," he says.

thiamin's ability to make energy available for the body has ramifications for the brain. "If you dramatically reduce thiamin intake, you reduce the ability of the brain to use glucose. And if you reduce that, you have impaired mental function," says Gary E. Gibson, Ph.D., professor of neuroscience at Burke Medical Research Institute at Cornell University in White Plains, New York. A severe thiamin deficiency not only kills the brain cells responsible for memory but also may cause an increase in the protein that causes Alzheimer's disease, says Dr. Gibson.

thiamin deficiencies have also been found to cause mood changes, vague feelings of uneasiness, fear, disorderly thinking and other signs of mental depression--symptoms that researchers say often affect memory.

Using thiamin Safely

Although thiamin toxicity--its symptoms include itching, tingling and pain--has been caused by massive doses administered by injection, there has been no evidence of toxicity from oral thiamin, even when doses as high as 500 milligrams (333 times the Daily Value of 1.5 milligrams) were taken daily for a month. Experts say that excess thiamin is easily cleared by the kidneys.