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 the elderly, and children often do not get enough B6. In addition, evidence has been presented that current recommended daily intakes should be increased.
Vitamin B6 deficiency might be worsened by 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. Good sources of B6 include nutritional (torula) yeast, brewer’s yeast, 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.
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 in the blood of homocysteine, 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, current evidence for benefit with 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.
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 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 that 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.
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.
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.
Bibliography
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