Randomized controlled trials with a placebo comparator arm/group included in the meta-analysis.

Two out of the 20 studies contained a co-intervention in both arms as indicated.Abbreviations: M, male; F, female; NR, not reported or unclear; RLS, restless led syndrome; GISEs, gastrointestinal side-effects shown as percentage of patients that experience gastrointestinal side-effects; Hb, hemoglobin; FeSO4, ferrous sulfate group.(1) All trials were double-blind except Maghsudlu, 2008 [69](2) All participants were generally healthy and non-anaemic with the exception of Sutton, 2004 [41](3) Unless indicated all trials used standard ferrous sulfate (i.e. not modified-release) and daily posology. Tardyferon® used in studies [59,60](4) Co-intervention: folic acid in both groups.(5) Co-intervention: ascorbic acid in both groups.Randomized controlled trials with a placebo comparator arm/group included in the meta-analysis.