Can Double Fortification of Salt with Iron and Iodine Reduce Anemia, Iron Deficiency Anemia, Iron Deficiency, Iodine Deficiency, and Functional Outcomes? Evidence of Efficacy, Effectiveness, and Safety

BACKGROUND: Anemia, iron deficiency, and iodine deficiency are problems of important public health concern in many parts of the world, with consequences for the health, development, and work capacity of populations. Several countries are beginning to implement double fortified salt (DFS) programs to simultaneously address iodine and iron deficiencies. OBJECTIVE: Our objective was to summarize the evidence for efficacy and effectiveness of DFS on the full range of status and functional outcomes and across different implementation and evaluation designs essential to successful interventions. METHODS: We conducted a systematic review and meta-analysis of published and gray literature examining the effects of DFS on nutritional status, cognition, work productivity, development, and morbidity of all population groups. We searched for articles in Medline, Embase, CINAHL, Cochrane Central Register, and ProQuest for randomized trials, quasi-randomized trials, and program effectiveness evaluations. RESULTS: A total of 22 studies (N individuals = 52,758) were included. Efficacy studies indicated a significant overall positive effect on hemoglobin concentration [standardized mean difference (95% CI): 0.33 (0.18, 0.48)], ferritin [0.42 (0.08, 0.76)], anemia [risk ratio (95% CI): 0.80 (0.70, 0.92)], and iron deficiency anemia [0.36 (0.24, 0.55)]. Effects on urinary iodine concentration were not significantly different between DFS and iodized salt. The impact on functional outcomes was mixed. Only 2 effectiveness studies were identified. They reported programmatic challenges including low coverage, suboptimal DFS quality, and storage constraints. CONCLUSIONS: Given the biological benefits of DFS across several populations in efficacy research, additional evaluations of robust DFS programs delivered at scale, which consider effective implementation and measure appropriate biomarkers, are needed.