Vitamin B6 Disease Treatment

Vitamin B₆ supplements at pharmacologic doses (i.e., doses much larger than those needed to prevent deficiency) have been used in an attempt to treat a wide variety of conditions, some of which are discussed below. In general, well designed, placebo-controlled studies have shown little evidence of benefit from large supplemental doses of vitamin B₆.

Side effects of oral contraceptives

Because vitamin B₆ is required for the metabolism of the amino acid tryptophan, the tryptophan load test (an assay of tryptophan metabolites after an oral dose of tryptophan) was used as a functional assessment of vitamin B₆ status. Abnormal tryptophan load tests in women taking high-dose oral contraceptives in the 1960's and 1970's suggested that these women were vitamin B₆deficient. The abnormal results in the tryptophan load test led a number of clinicians to prescribe high doses (100-150 mg/day) of vitamin B₆ to women in order to relieve depression and other side effects sometimes experienced with oral contraceptives. However, most other indices of vitamin B₆ status were normal in women on high-dose oral contraceptives, and it is likely that the abnormality in tryptophan metabolism was not due to vitamin B₆ deficiency. A more recent study of women on the low-dose oral contraceptives prescribed currently showed no benefit of up to 150 mg/day of vitamin B₆ (pyridoxine) over a placebo in the prevention of side effects, such as nausea, vomiting, dizziness, depression, and irritability.

Premenstrual syndrome (PMS)

The use of vitamin B₆ to relieve the side effects of high-dose oral contraceptives led to the use of vitamin B₆ in the treatment of premenstrual syndrome (PMS). PMS refers to a cluster of symptoms, including but not limited to fatigue, irritability, moodiness/depression, fluid retention, and breast tenderness, that begin sometime after ovulation (mid-cycle) and subside with the onset of menstruation (the monthly period). A review of twelve placebo-controlled double-blind trials of vitamin B₆ in PMS concluded that evidence for a beneficial effect was weak. A more recent review of 25 studies of vitamin B₆ and PMS suggested that doses of vitamin B₆ up to 100 mg/day may be of value, but conclusions were limited by the poor quality of most of the studies evaluated.

Depression

Because a key enzyme in the synthesis of the neurotransmitters, serotonin and norepinephrine, is PLP-dependent, it has been suggested that vitamin B-6 deficiency may lead to depression. However, clinical trials have not provided evidence that vitamin B-6 supplementation is effective in the treatment of depression.

Morning sickness (nausea and vomiting in pregnancy)

Vitamin B₆ has been used since the 1940's to treat nausea during pregnancy. Vitamin B₆ was included in the medication, Bendectin, which was prescribed for the treatment of morning sickness, and later withdrawn from the market due to unproven concerns that it increased the risk of birth defects. Vitamin B6 itself is considered safe during pregnancy, and has been used in pregnant women without any evidence of fetal harm. The results of two double-blind placebo-controlled trials that used 25 mg of pyridoxine every 8 hrs for 3 days or 10 mg of pyridoxine every 8 hrs for 5 days suggest vitamin B₆ may be beneficial in alleviating morning sickness. Each study found a slight but significant reduction in nausea or vomiting in pregnant women. A recent systematic review of placebo-controlled trials for nausea of early pregnancy found vitamin B₆ to be somewhat effective. However, it should be noted that morning sickness also resolves without any treatment, making it difficult to perform well-controlled trials.

Carpal tunnel syndrome

Carpal tunnel syndrome causes numbness, pain, and weakness of the hand and fingers due to compression of the median nerve at the wrist. It may result from repetitive stress injury of the wrist or from soft tissue swelling, which sometimes occurs with pregnancy or hypothyroidism. Several early studies by the same investigator suggested that vitamin B₆ status was low in individuals with carpal tunnel syndrome and that supplementation with 100-200 mg/day over several months was beneficial. A recent study found decreased blood levels of PLP to be associated with increased pain, tingling, and nocturnal wakening, all symptoms of carpal tunnel syndrome, in men who were not taking vitamin supplements. Studies using electrophysiological measurements of median nerve conduction have generally failed to find an association between vitamin B₆ deficiency and carpal tunnel syndrome. While a few trials have noted some symptomatic relief with vitamin B₆ supplementation, double-blind placebo-controlled trials have not generally found vitamin B₆ to be effective in treating carpal tunnel syndrome.