Lin 2009.

Study characteristics
Methods	Individually randomised trial conducted in rural China
Participants	Eligibility: children aged 6 months to 7 years Excluded: children without informed consent or with acute and chronic diseases Sample: 132 children. Mean age 36.5 months. 50% boys
Interventions	3 intervention groups Experimental group I: vitamin A 100,000 IU every month for 3 months Experimental group II: beta‐carotene Control group: placebo (biscuits)
Outcomes	Mean vitamin A serum levels
Notes	We included the results for vitamin A group versus placebo only.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: "The 50 severe vitamin A deficient children and 82 marginal vitamin A deficient children were randomly divided into three groups respectively by using a table with randomly assorted digits". Comment: probably done.
Allocation concealment (selection bias)	Unclear risk	Comment: no methods of allocation concealment are described in the text.
Blinding (performance bias and detection bias) Blinding of participants	High risk	Quote: "Vitamin A intervening group were administered 100,000 IU vitamin A capsules … the beta‐carotene intervening group … was administered 4 mg purified beta‐carotene … dissolved in vegetable oil and dropped into a general little biscuit … the placebo group were just administered a general little biscuit". Comment: vitamin A and placebo were administered in 2 different forms. Vitamin A in capsule form while placebo was in the form of biscuits.
Blinding (performance bias and detection bias) Blinding of provider	High risk	Comment: vitamin A and placebo were administered in 2 different forms. Vitamin A in capsule form while placebo was in the form of biscuits.
Blinding (performance bias and detection bias) Blinding of outcome assessor	High risk	Comment: vitamin A and placebo were administered in 2 different forms. Vitamin A in capsule form while placebo was in the form of biscuits.
Incomplete outcome data (attrition bias)	Low risk	Comment: no dropouts reported, and numbers at baseline and follow‐up appeared to be the same.
Selective reporting (reporting bias)	High risk	Comment: use of clinic services, hospitalisation, cause‐specific morbidity not reported.
Other bias	Low risk	Comment: study appeared free of other bias.