A Cochrane review included 6 studies with a total of 192 subjects with restless legs syndrome (RLS). The primary outcome was restlessness or uncomfortable leg sensations, which was quantified using the IRLS severity scale in 4 trials and another RLS symptom scale in one trial. Combining data from the trials using the IRLS severity scale, there was no clear benefit from iron therapy (MD in IRLS severity scores of -3.79, 95% CI: -7.68 to 0.10, p = 0.06; 4 trials, n=139). However, the fifth trial did find iron therapy to be beneficial (median decrease of 3 points in the iron group and no change in the placebo group on a 10 point scale of RLS symptoms, p = 0.01; n=25). Quality of life was improved in the iron group relative to placebo in some studies but not others. Changes in periodic limb movements were not different between groups (measured in two studies). Objective and subjective sleep quality and daytime functioning were not different between treatment groups in the studies that assessed them. The single study of subjects with end stage renal disease (n=25) did show a benefit of therapy. Most trials did not require subjects to have co-morbid iron deficiency and several excluded patients with severe anemia. The single study that was limited to iron deficient subjects (n=60) did not show clear benefit of iron supplementation on RLS symptoms. Iron therapy did not result in significantly more side effects than placebo (RR 1.39, 95% CI 0.85 to 2.27).
Comment: The quality of the evidence is downgraded by indirectness (in 4 studies intravenous iron was used) and imprecise results (few patients with wide confidence intervals).
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