Chen 2013a.

Methods	Factorial design, individually randomised trial conducted in Chengdu City, China
Participants	Eligibility: children aged 3‐6 years, apparently good health, haemoglobin (Hb) concentration > 60 g/L, serum C‐reactive protein (CRP) < 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 were eligible for inclusion. Children with evidence of recent acute or chronic illnesses and/or Hb <60 g/L were excluded. Sample: 387 children were included in the study
Interventions	4 groups: Group I: received a 200,000 IU vitamin A capsule (as retinol) just once initially Group II: received ferrous sulfate (element Fe 1‐2 mg/kg) once daily for 6 months Group III: received a 200,000 IU vitamin A capsule once initially and ferrous sulfate (element Fe 1‐2 mg/kg) once daily for 6 months Group IV, as the placebo control group, received neither vitamin A nor ferrous sulfate
Outcomes	Incidence of diarrhoea and LRTI
Notes	The 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 (Chen 2013a) is the comparison between Vitamin A and placebo while the second data set (Chen 2013b) is the comparison between vitamin A + iron vs iron only. The data for meta‐analysis was taken from table 2 and we calculated the rate ratio based on the number of events in the intervention 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 do 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: the study seems to be free of other bias.