Abstract: A total of 33 trials (including 11 from the original 2008 review) involving 7453 participants were included in this review, with 28 trials providing suitable data for entry into meta-analysis. Although the interventions provided in these studies were very different from one study to another (participant numbers, duration of intervention, group versus individual intervention, setting), most of the studies were based on recognisable theoretical models, and we tried to be inclusive in considering the wide variety of available culturally appropriate health education. Glycaemic control (as measured by glycosylated haemoglobin A1c (HbA1c)) showed improvement following culturally appropriate health education at three months (mean difference (MD) -0.4% (95% confidence interval (CI) -0.5 to -0.2); 14 trials; 1442 participants; high-quality evidence) and at six months (MD -0.5% (95% CI -0.7 to -0.4); 14 trials; 1972 participants; high-quality evidence) post intervention compared with control groups who received 'usual care'. This control was sustained to a lesser extent at 12 months (MD -0.2% (95% CI -0.3 to -0.04); 9 trials; 1936 participants) and at 24 months (MD -0.3% (95% CI -0.6 to -0.1); 4 trials; 2268 participants; moderate-quality evidence) post intervention. Neutral effects on health-related quality of life measures were noted and there was a general lack of reporting of adverse events in most studies — the other two primary outcomes for this review. Knowledge scores showed improvement in the intervention group at three (standardised mean difference (SMD) 0.4 (95% CI 0.1 to 0.6), six (SMD 0.5 (95% CI 0.3 to 0.7)) and 12 months (SMD 0.4 (95% CI 0.1 to 0.6)) post intervention. A reduction in triglycerides of 24 mg/dL (95% CI -40 to -8) was observed at three months, but this was not sustained at six or 12 months. Neutral effects on total cholesterol, low-density lipoprotein (LDL) cholesterol or high-density lipoprotein (HDL) cholesterol were reported at any follow-up point. Other outcome measures (blood pressure, body mass index, self-efficacy and empowerment) also showed neutral effects compared with control groups. Data on the secondary outcomes of diabetic complications, mortality and health economics were lacking or were insufficient. Because of the nature of the intervention, participants and personnel delivering the intervention were rarely blinded, so the risk of performance bias was high. Also, subjective measures were assessed by participants who self-reported via questionnaires, leading to high bias in subjective outcome assessment. Culturally appropriate health education has short- to medium-term effects on glycaemic control and on knowledge of diabetes and healthy lifestyles. With this update (six years after the first publication of this review), a greater number of RCTs were reported to be of sufficient quality for inclusion in the review. None of these studies were long-term trials, and so clinically important long-term outcomes could not be studied. No studies included an economic analysis. The heterogeneity of the studies made subgroup comparisons difficult to interpret with confidence. Long-term, standardised, multi-centre RCTs are needed to compare different types and intensities of culturally appropriate health education within defined ethnic minority groups, as the medium-term effects could lead to clinically important health outcomes, if sustained.

Plain-language summary: This updated review found in the world literature 33 randomised controlled trials (RCTs) of culturally appropriate health education on diabetes that met the selection criteria (participants from a defined ethnic minority group living in a upper-middle-income or high-income country, over 16 years of age, diagnosed with type 2 diabetes mellitus and receiving a culturally tailored health education intervention). The median duration of the intervention was six months, and a total of 7453 participants were involved in the studies. Culturally appropriate health education improved blood sugar control among participants, compared with those receiving 'usual' care, at three, six, 12 and 24 months after the intervention was provided. Knowledge about diabetes improved, and participants attained healthier lifestyles. No information was available regarding complications of diabetes and death from any cause, and there was a general lack of reporting of adverse effects in most studies. Neutral effects were observed for health-related quality of life, blood lipids like cholesterol, blood pressure and weight. The costs of educational programmes were rarely analysed. Compared with the first review, performed in 2008 (11 studies), many more published studies were identified in this review (altogether 33 studies), strengthening the original findings that blood sugar control and knowledge of diabetes are improved when culturally appropriate health education is provided to people in ethnic minority groups diagnosed with diabetes. The effects of this improvement are shown in this update as lasting longer — up to 24 months after health education was provided in some trials. However, additional high-quality standardised RCTs of longer duration are needed, along with full evaluation of costs. Heterogeneity of the studies, in terms of populations studied, type and duration of health education provided, variety of outcomes measured and differences in timing of assessment, limits interpretation of our findings. Also, risk of bias was judged to be high for many outcomes. This evidence is up-to-date as of September 2013.