Smith 1999.

Methods	Factorial design, individually randomised trial conducted in Belize
Participants	Eligibility: children aged 2.2‐5.5 years were eligible for inclusion in the trial. Those with fever or serious respiratory illness were excluded. Sample: 51 children were randomised to 4 intervention groups. Mean age of the children was 46.3 months
Interventions	The 4 intervention groups were: Group I: vitamin A only (received 10,000 IU vitamin A) Group II: zinc only (received 70 mg zinc) Group III: vitamin A + zinc (received vitamin A and zinc in above mentioned dosage) Group IV: placebo Study duration: 6 months
Outcomes	Vitamin A serum level
Notes	—
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The children selected were randomly assigned to receive one of the following supplements once per week: placebo; Zn, 70 mg as Zn gluconate; vitamin A, 3030 RE as retinyl palmitate; or a combination of vitamin A and Zn." Comment: stated to be randomised, but no further data reported
Allocation concealment (selection bias)	Unclear risk	Comment: insufficient details provided
Blinding (performance bias and detection bias) Blinding of Participants	Unclear risk	Quote: "Supplements were ingested orally in an orange flavoured powder (10 g), Tangt (Kraft General Foods Inc, White Plains, NY 10625) prepared as a beverage dissolved in approximately 120 mL of water." Comment: stated to be "double‐blind" in the article keywords, but there appear to be no details about blinding methods in the text. The intervention (or no intervention in the placebo group) were diluted in the same solution, so presumably all groups were identical.
Blinding (performance bias and detection bias) Blinding of provider	Unclear risk	Comment: not adequately reported
Blinding (performance bias and detection bias) Blinding of outcome assessor	Unclear risk	Comment: not adequately reported
Incomplete outcome data (attrition bias)	Unclear risk	Comment: insufficient details provided; losses not accounted for by group and small sample size makes this especially relevant
Selective reporting (reporting bias)	Unclear risk	Comment: does not reference a protocol or trial registration number and does not state that all measured outcomes are reported
Other bias	Unclear risk	Comment: insufficient details provided