TABLE 1.
Pooled effect sizes and risk ratios for double fortified salt efficacy studies1
| Pooled effect sizes | Pooled risk ratios | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| N | Hemoglobin SMD | N | Hemoglobin MD (g/dL) | N | Ferritin SMD | N | Urinary iodine SMD | N | Anemia RR | N | Iron deficiency anemia RR | ||
| Overall | 22 | 0.33 (0.18, 0.48) | 22 | 0.44 (0.23, 0.64) | 8 | 0.46 (0.21, 0.71) | 7 | –0.37 (–0.88, 0.13) | 13 | 0.80 (0.70, 0.92) | 5 | 0.36 (0.24, 0.55) | |
| Quality | |||||||||||||
| Strong or moderate | 6 | 0.55 (0.18, 0.92) | 6 | 0.62 (0.25, 1.00) | 6 | 0.51 (0.19, 0.84) | 4 | –0.23 (–0.55, 0.09) | 5 | 0.58 (0.40, 0.84) | 5 | 0.36 (0.24, 0.55) | |
| Weak | 16 | 0.23 (0.09, 0.38) | 16 | 0.36 (0.12, 0.60) | 2 | 0.34 (0.19, 0.50) | 3 | –0.56 (–1.77, 0.64) | 8 | 0.91 (0.84, 0.99) | 0 | — | |
| Type of DFS | |||||||||||||
| 1a | 3 | 0.19 (–0.05, 0.43) | 3 | 0.23 (–0.04, 0.51) | 0 | — | 0 | — | 3 | 0.61 (0.27, 1.40) | 0 | — | |
| 1b | 3 | 0.18 (0.06, 0.31) | 3 | 0.20 (0.03, 0.38) | 3 | 0.37 (0.17, 0.57) | 2 | –0.05 (–0.52, 0.42) | 3 | 0.73 (0.48, 1.12) | 1 | 0.25 (0.10, 0.61) | |
| 2 | 9 | 0.19 (–0.03, 0.41) | 9 | 0.28 (–0.07, 0.63) | 0 | — | 1 | –1.78 (-1.95, -1.62) | 3 | 0.95 (0.89, 1.01) | 0 | — | |
| 3 | 2 | 0.34 (–0.05, 0.74) | 2 | 0.72 (–0.32, 1.76) | 0 | — | 1 | -0.09 (–0.23, 0.04) | 0 | — | 0 | — | |
| 4 | 1 | 0.91 (0.70, 1.13) | 1 | 1.10 (0.85, 1.35) | 1 | 1.17 (0.95, 1.39) | 1 | 0.06 (–0.15, 0.26) | 0 | — | 1 | 0.27 (0.16, 0.46) | |
| 5 | 3 | 0.64 (–0.06, 1.34) | 3 | 0.67 (0.04, 1.3) | 3 | 0.39 (0.06, 0.73) | 2 | –0.34 (–0.96, 0.28) | 3 | 0.54 (0.31, 0.93) | 3 | 0.50 (0.32, 0.76) | |
| Population | Infants | 2 | 0.03 (–0.27, 0.32) | 2 | 0.06 (–0.40, 0.52) | 0 | — | 0 | — | 1 | 0.23 (0.05, 0.95) | 0 | — |
| School-age children and adolescents | 12 | 0.35 (0.11, 0.60) | 12 | 0.43 (0.13, 0.73) | 6 | 0.55 (0.26, 0.84) | 6 | –0.42 (–1.01, 0.17) | 8 | 0.72 (0.55, 0.93) | 5 | 0.36 (0.24, 0.55) | |
| Nonpregnant women | 4 | 0.25 (0.07, 0.43) | 4 | 0.30 (0.10, 0.51) | 2 | 0.16 (–0.05, 0.37) | 0 | — | 3 | 0.76 (0.63, 0.91) | 0 | — | |
| Pregnant women | 2 | 0.59 (0.24, 0.95) | 2 | 0.69 (0.35, 1.03) | 0 | — | 0 | — | 1 | 0.91 (0.83, 1.01) | 0 | — | |
| Lactating women | 1 | 0.30 (–0.21, 0.81) | 1 | 0.50 (–0.41, 1.41) | 0 | — | 0 | — | 0 | — | 0 | — | |
| Men | 1 | 0.08 (–0.14, 0.30) | 1 | 0.12 (–0.21, 0.45) | 0 | — | 0 | — | 0 | — | 0 | — | |
| Average iron intake from DFS | ≤10 mg iron/(person·d) | 12 | 0.27 (0.09, 0.46) | 12 | 0.45 (0.13, 0.76) | 1 | 0.18 (–0.16, 0.52) | 2 | –0.94 (–2.59, 0.72) | 4 | 0.79 (0.58, 1.08) | 0 | — |
| >10 mg iron/(person·d) | 4 | 0.44 (0.09, 0.79) | 4 | 0.52 (0.10, 0.93) | 6 | 0.51 (0.19, 0.84) | 2 | –0.12(–0.46, 0.23) | 3 | 0.59 (0.25, 1.37) | 5 | 0.36 (0.24, 0.55) | |
| Baseline hemoglobin concentration | <11 g/dL | 10 | 0.23 (0.02, 0.43) | 10 | 0.34 (0.00, 0.67) | 1 | 0.18 (–0.16, 0.52) | 1 | –0.09 (–0.23, 0.04) | 4 | 0.91 (0.83, 1.00) | 0 | — |
| ≥11 g/dL | 11 | 0.41 (0.18, 0.65) | 11 | 0.53 (0.26, 0.81) | 6 | 0.56 (0.29, 0.84) | 6 | –0.42 (–1.01, 0.17) | 8 | 0.61 (0.43, 0.87) | 5 | 0.36 (0.24, 0.55) | |
| Baseline anemia prevalence | ≤50% | 6 | 0.28 (0.12, 0.44) | 6 | 0.40 (0.09, 0.72) | 3 | 0.46 (0.34, 0.59) | 4 | –0.64 (–1.46, 0.19) | 5 | 0.63 (0.38, 1.06) | 2 | 0.34 (0.20, 0.60) |
| >50% | 8 | 0.46 (0.15, 0.76) | 8 | 0.48 (0.17, 0.79) | 4 | 0.23 (0.00, 0.45) | 1 | –0.02 (–0.33, 0.30) | 8 | 0.84 (0.74, 0.95) | 2 | 0.43 (0.13, 1.38) | |
| Intervention duration | <12 months | 14 | 0.40 (0.20, 0.60) | 14 | 0.45 (0.23, 0.66) | 8 | 0.46 (0.21, 0.71) | 5 | –0.14 (–0.44, 0.16) | 13 | 0.80 (0.70, 0.92) | 5 | 0.36 (0.24, 0.55) |
| ≥12 months | 8 | 0.20 (–0.02, 0.43) | 8 | 0.42 (–0.03, 0.87) | 0 | — | 2 | –0.94 (–2.59, 0.72) | 0 | — | 0 | — | |
N represents the number of intervention-control contrasts. Values are effect sizes or risk ratios (95% CI). Urinary iodine effect sizes include only studies where the intervention group received DFS and the control group received iodized salt. Type 1a DFS refers to DFS that contains microencapsulated potassium iodide and ferrous fumarate; Type 1b contains encapsulated ferrous fumarate; Type 2 contains a refined iodized salt, ferrous sulfate, and a stabilizing compound; Type 3 contains ferrous sulfate with various chelating agents and encapsulated iodine; Type 4 contains encapsulated ferrous sulfate; and Type 5 contains micronized ferric pyrophosphate. Studies using Type 5 DFS were excluded from the stratified analyses by average iron intake from DFS because the lower bioavailability of iron from this type of DFS makes it noncomparable to the other types of salts. DFS, double fortified salt; MD, mean difference; RR, risk ratio; SMD, standardized mean difference.