Vitamin B6

Daily Value: 2 milligrams

Good Food Sources: Bananas, avocados, chicken, beef, brewer's yeast, eggs, brown rice, soybeans, oats, whole wheat, peanuts, walnuts

For more than 30 years, learning about vitamin B₆ has consumed much of John Marion Ellis's life. This retired M.D. from Mount Pleasant, Texas, has conducted studies and written papers about it. He has assembled notebooks containing the latest clinical findings. And of course, both he and his wife faithfully take B₆ supplements.

"Vitamin B₆ is as important to your body as oxygen and water," says Dr. Ellis. "Except it takes six weeks for B₆ to get functioning in there like it should."

More and more research is accumulating to support this point of view, says Dr. Ellis. From carpal tunnel syndrome and memory loss to diabetes and premenstrual syndrome, the list of conditions for which vitamin B₆--also called pyridoxine--is gaining acceptance as a possible treatment is long.

Vitamin B₆ serves the important purpose of ensuring that biological processes, including fat and protein metabolism, take place in the body. "In the absence of B₆, metabolism is basically altered," says Michael Ebadi, Ph.D., professor of pharmacology and neurology at the University of Nebraska College of Medicine in Omaha.

Vitamin B₆ is also important in brain function. This nutrient is vital in helping to create neurotransmitters, the chemicals that allow brain cells to communicate with one another, says Dr. Ebadi. As a result, a lack of B₆ impairs your memory, causing trouble with your ability to register, retain and retrieve information.

When it comes to diabetes, a shortage of vitamin B₆ has been linked to something called glucose intolerance, which is an abnormally high rise in blood sugar after eating. It may also impair the secretion of insulin and glucagon, the hormone that tells your pancreas when to stop producing insulin.

Shortages of the B vitamins can also lead to nerve damage in the hands and feet. Some studies indicate that people with diabetes experience less of the numbness and tingling of diabetes-caused nerve damage if they get supplemental amounts of B vitamins such as B₆ and B₁₂.

As for carpal tunnel syndrome, "you couldn't say enough about carpal tunnel and vitamin B₆," says Dr. Ellis. "The evidence is that positive." He contends that swelling and inelasticity of the sheath surrounding a nerve in the wrist may be caused by a lack of B₆. "B₆ helps you get rid of the extra water gain that causes carpal tunnel," he says. Another theory, backed up by two European studies, suggests that B₆ somehow short-circuits an angry nerve's ability to transmit pain signals.

Dr. Ellis says his research shows that numbness, tingling, swelling and pain in the knees, shoulders and arms--what he calls menopausal arthritis--may also be caused by low vitamin B₆.

Other potential uses of vitamin B₆ on the horizon: ending asthma attacks by lowering the body's histamine levels and defending against atherosclerosis by reducing a chemical in the blood that damages arterial walls. "We're just beginning to scratch the surface of what this vitamin can do," says Dr. Ellis.

Using Vitamin B₆ Safely

Even the foods richest in vitamin B₆--such as bananas, avocados, brewer's yeast and beef--provide barely a single milligram of B₆. But that doesn't necessarily mean you'll need to reach for a supplement, since the Daily Value is only two milligrams.

And if you do opt for a supplement, you should use caution. Too much vitamin B₆ has been linked to serious nerve disorders as well as to oversensitivity to sunlight, which produces a skin rash and numbness.

In one study, people took 6,000 milligrams of vitamin B₆ daily over a two-month period; in another, people took 2,000 milligrams daily for two months or more. The results were the same: The people suffered from severe loss of neuromotor coordination and muscle weakness that stopped a few months after they quit taking B₆. As a result, experts suggest consulting your doctor before taking more than 100 milligrams of B₆ a day. They also recommend getting this vitamin as part of a B-complex tablet that supplies the Daily Values of all of the B vitamins.

People who are undergoing levodopa therapy for Parkinson's disease should avoid vitamin B₆ supplements altogether. It has been found to reduce the drug's effectiveness.

On the other hand, certain drugs can cause a vitamin B₆ deficiency: isoniazid, for tuberculosis; cycloserine, an antibiotic for tuberculosis; and penicillamine, for Wilson's disease, lead poisoning, kidney stones and arthritis. If you are taking any of these drugs, you might want to talk to your doctor before taking a B₆ supplement.