The quality of evidence is downgraded by inconsistency (unexplained variability in results).
A Cochrane review included 13 studies with a total of 5 613 neonates, infants, and toddlers. The studies were conducted in low-, middle- and high-income countries. Eight studies were included in the meta-analysis (Table ). No significant effects were observed on Mental Development Index (MDI) or Psychomotor Development Index (PDI) of the Bayley Scales of Infant Development (BSID), but there was significant statistical heterogeneity, which was not adequately explained by subgroup analyses.
| Outcome | Participants (studies) | Placebo | Intervention (zinc) |
|---|---|---|---|
Mental Developmet Index (MDI)
| 2134 (8 studies) | The mean MDI ranged across control groups from 86.4 to 113 points | The mean MDI in the intervention groups was 0.50 lower (2.06 lower to 1.06 higher) |
Psychomotor Development Index (PDI)
| 2134 (8 studies) | The mean PDI ranged across control groups from 87.6 to 104.5 points | The mean PDI in the intervention groups was 1.54 higher (2.26 lower to 5.34 higher) |
Two studies provided data on motor milestone attainment. There was no significant difference in the time to attainment of milestones between the placebo group and the zinc supplementation group in either of the studies. No study provided data on cognition score or intelligence quotient (IQ) or on adverse effects of zinc supplementation.
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