Vitamin B6 (therapeutic uses)

DEFINITION: Organic compound used to treat specific health conditions.

PRINCIPAL PROPOSED USES: Nausea of pregnancy (morning sickness)

OTHER PROPOSED USES: Asthma, depression, heart disease prevention, human immunodeficiency virus support, kidney stones, monosodium glutamate sensitivity, photosensitivity, reducing homocysteine levels, rheumatoid arthritis, schizophrenia, seborrheic dermatitis, tardive dyskinesia, vertigo

PROBABLY NOT EFFECTIVE USES: Alzheimer’s disease, autism (combined with magnesium), carpal tunnel syndrome, diabetic neuropathy, eczema, premenstrual syndrome, side effects of oral contraceptives

Overview

Vitamin B₆ plays a major role in making proteins, hormones, and neurotransmitters—chemicals that carry signals between nerve cells. Because mild deficiency of vitamin B₆ is common, this is one vitamin that is probably worth taking as insurance. However, there is little evidence that taking vitamin B₆ above nutritional needs offers benefits in the treatment of any particular illnesses, except, possibly, nausea of pregnancy (morning sickness).

Requirements and Sources

Vitamin B₆ requirements increase with age. The official U.S. and Canadian recommendations for daily intake are as follows:

Infants aged 0 to 6 months (0.1 mg) and 7 to 12 months (0.3 mg); children aged 1 to 3 years (0.5 mg), 4 to 8 years (0.6 mg), and 9 to 13 years (1.0 mg); males aged 14 years to fifty years (1.3 mg); females aged 14 to 18 years (1.2 mg); women aged 19 to fifty years (1.3 mg); pregnant women (1.9 mg); and nursing women (2.0 mg).

Severe deficiencies of vitamin B₆ are rare, but mild deficiencies are extremely common. In a survey of 11,658 adults, 71 percent of men and 90 percent of women were found to have diets deficient in B₆. Vitamin B₆ is the most commonly deficient water-soluble vitamin in older adults, and children often do not get enough B₆. In addition, evidence has been presented that recommended daily intakes should be increased. Vitamin B₆ deficiencies can lead to anemia, cognitive impairment, depression, irritability, and neuropathy.

Vitamin B₆ deficiency might be worsened by the use of hydralazine (for high blood pressure), penicillamine (used for rheumatoid arthritis and certain rare diseases), theophylline (an older drug for asthma), monoamine oxidase (MAO) inhibitors, and the antituberculosis drug isoniazid (INH), all of which are thought to interfere with B₆ to some degree. Excessive alcohol consumption, poor kidney function, rheumatoid arthritis, and conditions that limit absorption of vitamins contribute to vitamin B₆ deficiencies. Good sources of B₆ include nutritional (torula) yeast, brewer’s yeast, yellowfin tuna, salmon, chickpeas, sunflower seeds, wheat germ, soybeans, walnuts, lentils, lima beans, buckwheat flour, bananas, and avocados.

Therapeutic Dosages

One study found that 30 milligrams (mg) of vitamin B₆ daily was effective for symptoms of morning sickness. While far above nutritional needs, this dosage should be safe. However, for the treatment of other conditions, B₆ has been recommended at doses as high as 300 mg daily. There are potential risks at this level of vitamin B₆ intake, and the typical daily maximum is around 100 mg per day. A very high dose of vitamin B₆ over an extended period can cause nerve damage and neuropathy, so care is advised when taking B vitamins.

Therapeutic Uses

The results of a large, double-blind, placebo-controlled study suggest that vitamin B₆ at a dose of 30 mg daily may be helpful for treating nausea in pregnancy (morning sickness). Vitamin B₆ has been proposed for numerous other uses but without much, if any, scientific substantiation. For example, the two most famous uses of vitamin B₆, carpal tunnel syndrome and premenstrual syndrome (PMS), have no reliable supporting evidence, and the best-designed studies found this vitamin ineffective for either of these purposes.

Higher intake of vitamin B₆ reduces the level of homocysteine in the blood, a substance that might accelerate cardiovascular diseases, such as heart disease, strokes, and related conditions. However, there is no meaningful evidence that reducing homocysteine is beneficial and considerable evidence that it is not.

A series of studies suggests that vitamin B₆ may be helpful for the treatment of tardive dyskinesia (TD). In the first study, a four-week, double-blind crossover trial of fifteen people, treatment with vitamin B₆ significantly improved TD symptoms compared with placebo. Benefits were seen beginning at one week of treatment. The subsequent follow-up study tested the benefits of vitamin B₆ used over a period of twenty-six weeks in fifty people with tardive dyskinesia, and once again, the supplement proved more effective than placebo.

For the following other conditions, evidence for the benefit of vitamin B₆ remains incomplete or contradictory: allergy to monosodium glutamate (MSG), asthma, depression, diabetes of pregnancy, human immunodeficiency virus (HIV) infection, photosensitivity, preventing kidney stones, schizophrenia, seborrheic dermatitis, tardive dyskinesia and other side effects of antipsychotic drugs, and vertigo.

Despite some claims in the media, vitamin B₆ has not shown benefit for enhancing mental function. Research investigating the benefits of B₆ in combination with folate and vitamin B₁₂ as a potential treatment for cognitive decline due to Alzheimer’s disease has also shown disappointing results. However, a study published in 2022 in the journal Human Psychopharmacology suggested that B₆ supplements may play a role in reducing anxiety.

One study failed to find B₆ at a dose of 50 mg daily helpful for rheumatoid arthritis, despite a general B₆ deficiency seen in people with this condition. Vitamin B₆, alone or in combination with magnesium, showed some early promise for the treatment of autism, but the best-designed studies failed to find it effective.

Additionally, current evidence suggests that vitamin B₆ is not effective for treating diabetic neuropathy or eczema or for helping control the side effects of oral contraceptives.

Scientific Evidence

Nausea and vomiting: Morning sickness. Vitamin B₆ supplements have been used for years by conventional physicians as a treatment for morning sickness. In 1995, a large double-blind study validated this use. A total of 342 pregnant women were given a placebo or 30 mg of vitamin B₆ daily. Subjects then graded their symptoms by noting the severity of their nausea and recording the number of vomiting episodes. The women in the B₆ group experienced significantly less nausea than those in the placebo group, suggesting that regular use of B₆ can be helpful for morning sickness. However, vomiting episodes were not significantly reduced.

At least three studies have compared vitamin B₆ to ginger for the treatment of morning sickness. Two studies found them to be equally beneficial, while the other found ginger to be somewhat better. However, because ginger is not an established treatment for this condition, these studies alone do not provide any additional evidence in favor of B₆.

Chemotherapy-induced nausea and vomiting. Researchers also investigated whether vitamin B₆ can reduce the nausea and vomiting that often accompanies chemotherapy. A total of 142 women with ovarian cancer who were undergoing chemotherapy were randomized into three groups: acupuncture plus B₆ injection into the P6 acupuncture point (located on the inside of the forearm, about two inches above the wrist crease), acupuncture alone, or B₆ alone. Those who received both acupuncture and B₆ experienced less nausea and vomiting compared with the other two groups.

Premenstrual syndrome. A properly designed double-blind study of 120 women found no benefit of vitamin B₆ for premenstrual syndrome (PMS). In this study, three prescription drugs were compared against vitamin B₆ (pyridoxine, at 300 mg daily) and placebo. All study participants received three months of treatment and three months of placebo. Vitamin B₆ proved to be no better than placebo.

Approximately a dozen other double-blind studies have investigated the effectiveness of vitamin B₆ for PMS, but none were well designed; overall, the evidence for any benefit is weak at best. Some books on natural medicine report that the negative results in some of these studies were due to insufficient B₆ dosage, but in reality, there was no clear link between dosage and effectiveness. However, preliminary evidence suggests that the combination of B₆ and magnesium might be more effective than either treatment alone. The overall evidence for treating PMS with vitamin B₆ is weak, and it likely is most effective in individuals lacking the vitamin in their diet.

Autism. One double-blind, placebo-controlled crossover study found indications that very high doses of vitamin B₆ may produce beneficial effects in the treatment of autism. However, this study was small and poorly designed; furthermore, it used a dose of vitamin B₆ so high that it could cause toxicity.

It has been suggested that combining magnesium with vitamin B₆ could offer additional benefits, such as reducing side effects or allowing a reduced dose of the vitamin. However, the two reasonably well-designed studies using combined vitamin B₆ and magnesium have failed to find benefits. Therefore, it is not possible at present to recommend vitamin B₆ with or without magnesium as a treatment for autism.

Asthma. A double-blind study of seventy-six children with asthma found significant benefit from vitamin B₆ after the second month of usage. Children in the vitamin B₆ group were able to reduce their doses of asthma medication (bronchodilators and steroids). However, a recent double-blind study of thirty-one adults who used either inhaled or oral steroids did not show any benefit. The dosages of B₆ used in these studies were quite high, in the range of 200 to 300 mg daily. Because of the risk of nerve injury, it is not advisable to take this much B₆ without medical supervision. Further research found vitamin B₆ was of the most benefit to individuals with asthma who were steroid-dependent.

Safety Issues

The safe upper levels for daily intake of vitamin B₆ are as follows:

Children aged 1 to 3 years (30 mg), 4 to 8 years (40 mg), 9 to 13 years (60 mg), and 14 to 18 years (18 mg); adults (100 mg); pregnant girls (80 mg); and pregnant women (100 mg).

At higher dosages, especially above 2 g daily, there is a very real risk of nerve damage. Nerve-related symptoms have even been reported at doses as low as 200 mg. (This is a bit ironic, given that B₆ deficiency also causes nerve problems.) In some cases, very high doses of vitamin B₆ can cause or worsen acne symptoms.

In addition, doses of vitamin B₆ over 5 mg may interfere with the effects of the drug levodopa when it is taken alone. However, vitamin B₆ does not impair the effectiveness of drugs containing levodopa and carbidopa. Maximum safe dosages for individuals with severe liver or kidney disease have not been established.

Important Interactions

People who are taking isoniazid (INH), penicillamine, hydralazine, theophylline, or MAO inhibitors may need extra vitamin B₆, but they should take only nutritional doses. Higher doses of B₆ might interfere with the action of the drug. People who are taking levodopa without carbidopa for Parkinson’s disease should not take more than 5 mg of vitamin B₆ daily, except on medical advice. In addition, B₆ might reduce the side effects for people taking antipsychotic medications. The tuberculosis medication Cycloserine increases the body’s excretion of vitamin B₆ in the urine, which may lead to deficiencies. Similarly, drugs commonly used for seizure disorders may increase the catabolism of vitamin B₆, causing levels to deplete.

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