Aim  There is increasing interest in the role that peers may play to support positive health behaviours in diabetes, but there is limited evidence to inform policy and practice. The aim of this study was to systematically review evidence of the impact and effectiveness of peer support in adults living with diabetes.

Methods  We searched the Cochrane Library, MEDLINE, PubMed, EMBASE and CINHAL for the period 1966–2011, together with reference lists of articles for eligible studies. Data were synthesized in a narrative review.

Results  Twenty-five studies, including fourteen randomized, controlled or comparative trials, met the inclusion criteria. There was considerable heterogeneity in the design, setting, outcomes and measurement tools. Peer support was associated with statistically significant improvements in glycaemic control (three out of 14 trials), blood pressure (one out of four trials), cholesterol (one out of six trials), BMI/weight (two out of seven trials), physical activity (two out of five trials), self-efficacy (two out of three trials), depression (four out of six trials) and perceived social support (two out of two trials). No consistent pattern of effect related to any model of peer support emerged.

Conclusions  Peer support appears to benefit some adults living with diabetes, but the evidence is too limited and inconsistent to support firm recommendations. There remains a need for further well-designed evaluations of its effectiveness and impact. Key questions remain over its suitability to the needs of particular individuals, populations and settings, how best to implement its specific components and the sustainability of its effects.