Chen 2013a.

Study characteristics
Methods	Factorial design, individually randomised trial conducted in Chengdu City, China
Participants	Eligibility: children aged 3–6 years, apparently good health, haemoglobin concentration > 60 g/L, serum C‐reactive protein < 10 mg/L, parental or guardian's approval for participation and parental or guardian's agreement to avoid additional use of vitamin A and iron supplements during the investigation Excluded:  children with evidence of recent acute or chronic illnesses or haemoglobin < 60 g/L (or both) Sample: 387 children
Interventions	4 intervention groups Experimental group I: vitamin A 200,000 IU capsule (as retinol) just once initially Experimental group II: ferrous sulphate (elemental iron 1–2 mg/kg) once daily for 6 months Experimental group III: vitamin A 200,000 IU capsule once initially and ferrous sulphate (elemental iron 1–2 mg/kg) once daily for 6 months Control group: neither vitamin A nor ferrous sulphate
Outcomes	Incidence of diarrhoea and LRTI
Notes	Study setting was a periurban area in Huayuan Town, Pixian County of Chengdu City, Sichuan Province, western China, from March to September 2011. Supplementation was given in schools. The paper did not have a study flow diagram. The data from the factorial design were included in 2 data sets. The first data set is the comparison between vitamin A and placebo  (Chen 2013a), while the second data set is the comparison between vitamin A + iron vs iron only  (Chen 2013b). The data for meta‐analysis was taken from table 2 and we calculated the rate ratio based on the number of events in the experimental and control groups with the denominator as person‐days at risk.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The RAND function of Excel (Microsoft, Redmond, WA, USA) was used to generate computer randomly permutated codes".
Allocation concealment (selection bias)	Low risk	Quote: "The health care workers, outcome assessors, data analyst and children were not made aware of the intervention assignment until the completion of data analysis". Comment: probably done.
Blinding (performance bias and detection bias) Blinding of participants	Low risk	Quote: "Children were not made aware of the intervention".
Blinding (performance bias and detection bias) Blinding of provider	Low risk	Quote: "The health care workers, outcome assessors, data analyst and children were not made aware of the intervention …".
Blinding (performance bias and detection bias) Blinding of outcome assessor	Low risk	Quote: "… outcome assessors, data analyst and children were not made aware of the intervention …"
Incomplete outcome data (attrition bias)	Low risk	Comment: loss to follow‐up was 13% and balanced in each group with similar reasons for attrition.
Selective reporting (reporting bias)	Unclear risk	Comment: the trial registration number was not given. Authors did mention that they could not report some of the a priori mentioned serum biochemical markers, as they could not collect enough blood samples.
Other bias	Low risk	Comment: study appeared free of other bias.