Naeini 2014.

Methods	2‐arm, parallel group, randomised, controlled trial, 1 year duration
Participants	Location: Iran. Single centre. Setting of recruitment and treatment: Tehran University, School of Nutritional Sciences and Dietetics. Sample size: Number randomised: 148 in intervention, 148 in comparator (total 296). Number completed: 127 in intervention, 129 in comparator (total 256). Participant (baseline) characteristics: Age in years (mean ± SD): 66.5 ± 0.39 in vitamin supplementation group, 66.3 ± 0.38 in control group. Sex: 53% female among study completers. Inclusion criteria: MMSE scores between 21 and 26; Minimum education to fifth grade; Age between 60 and 75 years. Exclusion criteria: Dementia, depression, or epilepsy; Mental retardation, history of brain surgery, or any significant neurological disease; Severe cardiovascular disease and severe anaemia; Severe kidney or liver disease, inflammatory intestinal disease, and any disease that interfered with the antioxidant's absorption; Consumption of antioxidant medication or vitamin that might modify the results; BMI more than 30; Special diet (vegetarian, vegan, etc.); Smoking; Addicted to alcohol; Using neuroleptic drugs, benzodiazepine, immunosuppressant, anti‐depression and anticonvulsants medication; Current medication known to influence vitamin E and C status (laxatives and hormone replacement therapy).
Interventions	Active intervention: 300 mg of vitamin E (Dl‐alpha‐ tocopherol acetate) plus 400 mg vitamin C (ascorbic acid) daily for a year. Comparator: Placebo.
Outcomes	Outcomes of interest in the review: Overall cognitive function: MMSE.
Source of Funding	This study was supported by Institute of Nutritional Sciences, University of Vienna and the Vice‐chancellor for Research, Tehran University of Medical Sciences (TUMS), Iran, by a Grant (No. 11126).
Declaration of Interest	"The authors declare that there are no conflicts of interest".
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "The MCI subjects were divided to two groups according to their gender (male or female), each of them were further divided to three age groups including 60‐65, 65‐70, and 70‐75 years. The subjects within each of these six groups were then further divided to two equally numbered supplemented or placebo subgroups by simple randomization". Comment: Insufficient information about sequence generation process.
Allocation concealment (selection bias)	Unclear risk	Comment: No information – allocation concealment not described.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Described as "double‐blind". Quote: “One group consumed 300 mg of vitamin E (Dl‐alpha‐ tocopherol acetate) plus 400 mg vitamin C (ascorbic acid) per day, and the second group consumed placebo with the identical condition over the 1‐year intervention period". Comment: Unclear from this whether appearance of supplements and placebo were identical.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "Evaluation of cognitive function by MMMSE was blindly performed by an expert psychologist." Comment: Blinded outcome assessor.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Quote: “Of the 761 volunteers, 296 were found to have MCI and selected for the next part of the study. From these, 40 did not continue with the study due to the problems tolerating the supplementations (14 subjects), 1 subject died, and 25 subjects abstained to continue participation due to personal reasons. 148 were randomised to each group and 256 subjects completed the study.” 21/148 in the vitamins group and 19/148 in the placebo group did not complete. Comment: The participants who did not complete the trial (40/296, 13.5%) were not included in the analysis. Reason for exclusion was not described based on the allocated group.
Selective reporting (reporting bias)	Low risk	Comment: Outcomes specified in the methods section were reported. No access to trial protocol.
Other bias	Low risk	No other risks identified.