Abstract
Nutritional deficiencies are prevalent in populations across the world. Fortification of staple foods has been used as an alternative to supplementation to address many deficiencies. One such staple is salt, which has long been fortified with iodine, but more recently with iron, folate, and other micronutrients. Our objective was to determine the effects of fortified salt on nutritional and health outcomes among children, adolescents, and adults. We conducted a systematic review of published and unpublished literature using a pre-defined search strategy. Abstracts and full texts were screened for randomized trials, quasi-randomized trials, and pre-post-designs of double or multiple fortified salt. We calculated the weighted pooled effect sizes for the effects of fortified salt on nutritional and health outcomes. Of the 395 studies identified, 33 (including 37 intervention-control comparisons) fit our inclusion criteria. Of these comparisons, 26 studied the effects of salt fortified with iron and iodine [double fortified salt (DFS)], 2 studied the effects of salt fortified with folic acid and iodine, 1 studied the effect of triple fortified salt, 1 studied the effect of quadruple fortified salt, and 7 studied the effects of multiple micronutrient fortified salt (MMFS; fortified with ≥5 nutrients). Pooled effect sizes indicated positive effects from all iron-containing fortified salt on hemoglobin concentration [standardized mean difference (95% confidence interval): DFS 0.36 (0.22, 0.50), n comparisons = 26; triple fortified salt 1.56 (1.42, 1.70), n comparisons = 1; quadruple fortified salt 0.33 (0.02, 0.63), n comparisons = 1; MMFS 0.23 (0.03, 0.43), n comparisons = 6]. DFS and MMFS reduced the odds of anemia and iron deficiency (ID) anemia. MMFS improved serum folate and reduced the odds of ID. Pooled effects on biomarkers of vitamin B12, vitamin A, and zinc status varied by type of salt, but were largely not significant. Fortification of salt with iodine and iron, with and without other nutrients, is effective in increasing hemoglobin and reducing the odds of anemia and ID in population-based studies.