Make up a list of health problems that each vitamin or mineral is supposed to help, and there’s a good chance that the list for vitamin B₆ will be the longest. This essential B vitamin has been recommended for everything from kidney stones and morning sickness to diabetes and PMS.

While it may actually help some of these conditions, there’s just not enough scientific evidence yet to nail down many of its benefits, says James Leklem, Ph.D., professor of nutrition and food management at Oregon State University in Corvallis.

Like other vitamins and minerals, B₆ works with enzymes, the chemical spark plugs that start reactions in the body. It is an essential part of more than 100 enzymes that are involved in the production of energy and protein. B₆ has to be on hand when your body breaks down stored sugar for energy, when it creates the building blocks that will become protein, and when it makes the brain and nervous system of a developing fetus. Research also suggests that B₆ can help reduce the risk of heart disease and complications of diabetes.

If we eat more food than we need for immediate energy, some of the excess calories are converted to a form of glucose (blood sugar) called glycogen, which is stored in the liver and muscles. When blood sugar drops, glycogen is broken down into glucose and used for fuel. The enzyme that does this requires B₆.

People start to use glycogen for energy if they’ve been exercising for an hour or longer or if they’re dieting to lose weight. "But you’d have to be extremely deficient in vitamin B₆ to have a problem breaking down glycogen," Dr. Leklem says. "Most people just don’t have this problem."

Vitamin B₆ also helps link the molecules that make up certain amino acids, Dr. Leklem explains. Strung together like pearls, amino acids are the "bits" that make proteins. So B₆ indirectly aids protein production in the body.

This vitamin also helps link the molecules of nucleic acids, which make up our cells’ genetic material. Low B₆ levels can slow down amino acid or nucleic acid production enough to lead to impaired immunity. In extreme cases, the deficiency can lead to a rare condition called sideroblastic anemia, Dr. Leklem says.

Our bodies need vitamin B₆, along with vitamin B₁₂ and folic acid, to be able to break down a potentially toxic amino acid by-product called homocysteine. "High levels of homocysteine have been associated with increased risk of heart disease and stroke," says Alan Gaby, M.D., professor of nutrition at Bastyr University in Bothell, Washington. Compared with B₁₂ and folic acid, however, B₆ seems to play a lesser role, according to Dr. Gaby. "Only about 15 percent of people with high homocysteine levels respond to B₆," he says.

A study from the Harvard School of Public Health showed that women who got at least 3 milligrams a day of B₆ had half the risk of having heart attacks compared with women who got 1.5 milligrams. This is still more than a woman’s average daily intake of B₆, which is about 1.2 milligrams.

Vitamin B₆ also helps out neurotransmitters, the chemicals that our nervous systems produce in order to send out messages. It is needed to make an impressive array of neurotransmitters that help to activate and speed up communication among nerve cells. These include serotonin, taurine, dopamine, norepinephrine, and histamine.

"Unfortunately, there’s not much research to tell us what all this may mean in terms of actual mental performance," Dr. Gaby says. But there is some. Higher blood concentrations of B₆ were associated with better performance on two tests of memory in a study by researchers at Tufts University in Boston.

Vitamin B₆ plays a role in maintaining normal hormone balance. When B₆ levels are low, hormones may have a stronger-than-normal action on specific cells or organs, Dr. Leklem says. In animals, the vitamin inhibits the way a hormone hooks up or binds within a cell, which is a step in the cell’s activation. "In humans, however, we don’t know for sure how it works," Dr. Leklem says.

Still, B₆ is known to help regulate a number of specific hormones, including estrogen, progesterone, androgen (a male hormone), and glucocorticoid (a stress hormone.) This may be a reason that the vitamin sometimes seems to be an effective treatment for PMS and morning sickness, says Dr. Leklem.

For different reasons, vitamin B₆ may also be able to help people who have diabetes. One result of this disease is that blood sugar has the ability to stick to proteins, a process called glycosylation. "It’s fairly well accepted that glycosylation of proteins is one of the things that causes the complications of diabetes, such as kidney and nerve damage and cataracts," Dr. Gaby says.

In a study at Yale University, researchers found that people with diabetes got some benefits from taking a B₆ supplement because of its apparent effect on glycosylation. When they took 50 milligrams of B₆ three times a day for six weeks, the participants had significant drops in the glycosylation of hemoglobin, a protein found in red blood cells.

Vitamin B₆ deficiency has been linked to glucose intolerance, a condition in which blood sugar rises sharply after eating. It has also been implicated in impaired secretion of insulin and glucagon, both hormones that are essential in regulating blood sugar levels.

Blood levels of B₆ are low in 20 to 25 percent of people with diabetes, and in some, levels fall abruptly when they are given sugar, Dr. Leklem says. "We don’t know why this happens, but we do know that there are several good reasons that people with diabetes should make sure they are getting enough B₆. Preventing diabetes-related organ damage is apparently one of them."

Vitamin B₆ interacts with magnesium, an essential mineral used in more than 300 biochemical reactions in the body. In some cases, both the vitamin and the mineral are needed to activate the enzymes that start biochemical reactions such as breaking down sugar for energy. Some research also suggests that B₆ depends on magnesium to help it get inside cells, where it can do its work. "One thing we do know is that an extremely low intake of magnesium will compromise the body’s ability to use B₆ properly," Dr. Leklem says.

The vitamin also interacts with oxalate, a by-product of metabolism that plays an important role in the formation of kidney stones.

Some people who develop kidney stones have a genetic abnormality that leads to a buildup of oxalate, and high concentrations in the kidneys cause it to form stones. Taking B₆ at doses of 10 to 50 milligrams a day can help, Dr. Gaby says. "And taking magnesium along with the B₆ is probably warranted," he adds. In his view, the magnesium helps prevent oxalate from crystallizing into stones. Your doctor should determine whether taking B₆ and magnesium would be beneficial if you’ve been diagnosed with kidney stones.

The more protein you eat, the more vitamin B₆ you need, because this vitamin assists in protein metabolism. Some protein foods contain good amounts of B₆, but you can’t count on all protein-rich foods as super suppliers. Good sources include meats, fish, poultry, shellfish, legumes, fruits, whole grains, and leafy green vegetables. Dairy products, on the other hand, are relatively poor sources, and processed luncheon meats like sliced ham or turkey lose 50 to 70 percent of their B₆ in processing.

Alcoholics are most likely to be deficient, because alcohol actually promotes the destruction of B₆ and its loss from the body. If you’re elderly and don’t eat well for any reason, you’re more likely than a younger person to have a deficiency. Others who might have a problem are people with absorption problems such as celiac disease and those who take drugs that interfere with the body’s use of B₆.

More than 40 drugs can compromise absorption, including isoniazid (Laniazid, Nydrazid), a tuberculosis drug, and penicillamine (Cuprimine, Depen), used to treat Wilson’s disease and rheumatoid arthritis and to prevent kidney stones. "Birth control pills used to be on the list of possible B₆ antagonists, but the new, low-estrogen pills don’t cause this problem," Dr. Leklem says.

People who are short on B₆ are likely to be weak and irritable and have trouble sleeping. They may also develop depression, impaired glucose tolerance, convulsions, cracking of the lips and tongue, and skin problems such as seborrhea or eczema.

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