Clinical Abstracts
Clinical Abstracts
July 1999; Volume 1: 63
With Comments from Adriane Fugh-Berman, MD
Vitamin B6 and PMS
Source: Wyatt KM, et al. Efficacy of vitamin B6 in the treatment of premenstrual syndrome: A systematic review. BMJ 1999;318:1375-1381.
Summary: This systematic review identified 25 published trials of PMS and vitamin B6. Studies of cyclical mastalgia were included, and studies of multivitamins were included if the treatment contained at least 50 mg of vitamin B6. Ten randomized, placebo-controlled, double-blind, parallel or crossover studies were included. Two analyses were conducted—one of 10 trials and one of nine trials (one trial was excluded because of "statistical heterogeneity").
Results: Only three of 10 trials scored >3 on the Jadad scale (a measure of methodological quality). None of the trials included a power calculation; and only three of 10 trials noted the number of and reasons for withdrawals. Using a random effects model, the overall odds ratio (OR) in favor of vitamin B6 in the analysis of all 10 trials was 1.57 (95% confidence interval 1.40-1.77). The anal-ysis of nine trials (934 patients) resulted in an OR of 2.32 (1.95-2.54) in favor of vitamin B6. Data on depressive symptoms were extracted from five trials; the overall OR in favor of vitamin B6 was 2.12 (1.80-2.48). There was no dose-response effect. One patient taking 600 mg/d of vitamin B6 reported neurological side effects.
Comment: This is a difficult subject for meta-analysis. No consensus exists on criteria for diagnosing or treating PMS, and the B6 trials demonstrate little consistency in inclusion criteria, doses, formulations, and use of concurrent medications. Only two studies enrolled more than 55 people; the largest study (434 women) included those on psychotropics, analgesics, diuretics, and oral contraceptives (at least two other trials also included oral contraceptive users); vitamin B6 doses ranged from 50-600 mg/d; and outcome measures included the vague ("tiredness") and the strange ("violence," "stomach ache," "coordination"). The authors kept dropping inclusion criteria in order to have anything to analyze. After creating a quality screen based on both the Jadad criteria and their own scale, they write "as none of the trials met both our and the Jadad quality criteria, we did not take the quality score into account when considering trials for inclusion."
There is a discrepancy between the text and a table; although it is stated that only double-blind trials are included in this review, a table notes that one study was "blinded to patient only."
As Alvin Feinstein wrote about meta-analysis, "Among the many virtues that have been extolled for meta-analysis, the main appeal is that it can convert existing things into something better."1 An aggregation of data from flawed trials cannot be used to draw conclusions.
References
1. Feinstein AR. Meta-analysis: Statistical alchemy for the 21st century. J Clin Epi 1995;48:71-79.
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