Women frequently take large daily doses of vitamin B6 for premenstrual syndrome (PMS), even though nutritional deficiency of this vitamin is rare. The recommended dietary allowance is about 2 mg per day; high intake has been associated with severe toxicity, including neuropathy. An intake of 200 mg per day may cause reversible damage, and an intake of 2,000 mg per day or greater is associated with peripheral neuropathy. In some European countries, the quantity of vitamin B6 that may be purchased or prescribed has been restricted to reduce the risk of toxicity from excessive use. Wyatt and colleagues reviewed the evidence for benefit of vitamin B6 in PMS in light of concerns about potential toxicity from excessive uncontrolled use.
The authors searched literature and data sources for reports of treatment of PMS and use of vitamin B6. They also reviewed references of all articles found and contacted manufacturers and researchers for unpublished relevant data. All trials found were assessed by two techniques to establish methodologic quality and subjected to funnel-plot analysis to detect bias. Of the 25 trials identified, four were excluded because they did not use a placebo group, two were excluded because they were retrospective and nine were excluded because the quantitative data could not be analyzed.
Only one of the remaining 10 trials provided details of the method for randomization. None of the trials met criteria for quality. The number of participants ranged from 31 to 434. The trials used dosages of 50 to 600 mg per day of vitamin B6 in a variety of regimens and often in combination with other agents. Exclusion criteria varied, as well as information the trials provided about participants, particularly their use of hormone preparations.
In spite of concerns about the quality of the studies, the authors calculated odds ratios for improvement in all premenstrual symptoms and specifically in depressive symptoms. Overall, the analysis provided an odds ratio of 1.57 showing benefit for use of vitamin B6 in PMS. One trial was significantly different from the others and when this trial was excluded from the calculation, the odds ratio improved to 2.32 in favor of vitamin B6 use to improve overall symptoms. Five trials evaluated vitamin B6 for symptoms of premenstrual depression; the overall odds ratio was 2.12, but this ratio fell to 1.69 when one outlying trial was excluded from the analysis. Only one of the more than 900 patients in the trials reported symptoms possibly attributable to neuropathy.
The authors stress that no randomized controlled trials of adequate quality could be identified to support a definitive conclusion about the efficacy of vitamin B6 in treating PMS. The limited evidence from published research indicates that 100 mg of vitamin B6 daily may relieve overall symptoms better than a placebo. Less evidence was available to support dosages of 50 mg per day. Premenstrual depression may also be relieved by 50 to 100 mg of vitamin B6. Well-designed controlled trials are needed to clarify the possible benefits and side effects of vitamin B6 in the treatment of PMS.