IDPP‐1 2006.

Methods	Parallel randomised controlled trial, randomisation ratio 1:1:1:1
Participants	Inclusion criteria: IGT (mean 2‐hour plasma glucose after OGTT 140 mg/dL to 199 mg/dL (7.8 mmol/L to 11.0 mmol/L) and FPG < 126 mg/dL (7.0 mmol/L)) (WHO 1999); no major illness; 35 to 55 years Exclusion criteria: diagnosis of T2DM during recruitment; pregnancy Diagnostic criteria: IGT (WHO 1999)
Interventions	Number of study centres: ‐ Run‐in period: none Administration‐free period before testing during trial: not reported Titration period: none
Outcomes	Composite outcome measures reported: yes (cardiovascular disease)
Study details	Trial terminated before regular end (for benefit/because of adverse events): yes; Quote from publication: "After a median follow‐up period of 30 months, because there were significant differences in the outcome measure between the control and intervention groups, the committee recommended the termination of the study in December 2004" Taking trial drug on glycaemic testing days: not specified
Publication details	Language of publication: English Funding: commercial (M/S US Vitamins) Publication status: peer‐reviewed journal
Stated aim of study	Quote from publication: "In a prospective community‐based study, we tested whether the progression to diabetes could be influenced by interventions in native Asian Indians with IGT who were younger, leaner and more insulin resistant than the above populations"
Notes	Two more intervention groups existed that were not included in this review; 1) metformin and 2) diet plus physical activity combined with metformin
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote from publication: "A randomised, controlled clinical trial was performed in subjects who were......" Comment: insufficient information about the sequence generation process
Allocation concealment (selection bias)	Unclear risk	Comment: no description of allocation concealment
Blinding of participants and personnel (performance bias) all‐cause mortality/cardiovascular mortality	Low risk	Quote from publication: "Masking: Open Label" and "However, the principal investigators were blinded to the outcome until they were asked to close the study by the international data monitoring committee." Comment: outcome evaluated by an independent outcome committee. Outcome unlikely to be influenced by lack of blinding
Blinding of participants and personnel (performance bias) incidence of T2DM	Low risk	Quote from publication: "Masking: Open Label" "However, the principal investigators were blinded to the outcome until they were asked to close the study by the international data monitoring committee." Comment: outcome evaluated by an independent outcome committee and investigator‐assessed outcome measure
Blinding of participants and personnel (performance bias) measures of blood glucose control	Low risk	Quote from publication: "Masking: Open Label" and ""However, the principal investigators were blinded to the outcome until they were asked to close the study by the international data monitoring committee." Comment: investigator‐assessed outcome measure, unclear if this outcome also was assessed by the blinded independent outcome committee. The outcome is not likely to be influenced by lack of blinding
Blinding of outcome assessment (detection bias) all‐cause mortality/cardiovascular mortality	Low risk	Quote from publication: "However, the principal investigators were blinded to the outcome until they were asked to close the study by the international data monitoring committee." Comment: outcome evaluated by an independent outcome committee
Blinding of outcome assessment (detection bias) incidence of T2DM	Low risk	Quote from publication: "However, the principal investigators were blinded to the outcome until they were asked to close the study by the international data monitoring committee." Comment: outcome evaluated by an independent outcome committee and investigator‐assessed outcome measure
Blinding of outcome assessment (detection bias) measures of blood glucose control	Low risk	Quote from publication: "However, the principal investigators were blinded to the outcome until they were asked to close the study by the international data monitoring committee." Comment: investigator‐assessed outcome measure, unclear if this outcome also was assessed by the blinded independent outcome committee. The outcome is not likely to be influenced by lack of blinding
Blinding of outcome assessment (detection bias) non‐serious adverse events	High risk
Incomplete outcome data (attrition bias) all‐cause mortality/cardiovascular mortality	Unclear risk	Comment: unknown whether mortality status was known on the participants lost to follow‐up. The proportion of missing outcomes compared with observed event risk may have a clinically relevant impact on the intervention effect estimate
Incomplete outcome data (attrition bias) incidence of T2DM	Unclear risk	Comment: the proportion of missing outcomes compared with observed event risk is not enough to have a clinically relevant impact on the intervention effect estimate
Incomplete outcome data (attrition bias) measures of blood glucose control	Unclear risk	Comment: Insufficient information to assess whether missing data in combination with the method used to handle missing data were likely to induce bias
Selective reporting (reporting bias)	High risk	Quote from publication: "An internal safety committee monitored the adverse events and safety of study protocol. The data and final outcome measures were monitored by the international monitoring committee who had looked at the results three times, i.e. when 500 subjects had completed the follow‐up assessments at 12, 24 and 30 months. The principal investigators were blinded to the interim results." Comment: several outcomes with relevance for this review are not reported or only reported in a format which makes them unsuitable for meta‐analyses, e.g. adverse events
Other bias	Unclear risk	Comment: role of funding source not described