The original study was a cluster randomised trial, started in 1986, in which 33 clinics in Da Qing, China, were randomly assigned to either be a control clinic or provide one of three interventions (diet, exercise, or diet plus exercise) for 6 years for adults with impaired glucose tolerance. Subsequently, participants were followed for up to 30 years.
According to a commentary, the Da Qing study is one of the most celebrated trials in the medical literature, for very good reasons- it was done in China, unusual in itself among major clinical trials, and started in 1986, with great foresight since the prevalence of type 2 diabetes at that time was very low, but the investigators and funders recognised that the incidence was likely to rise substantially. It notes the results from the Da Qing study have been consistently positive, showing that the costly and debilitating epidemic of type 2 diabetes is at least partly preventable by simple, low-cost lifestyle measures and the current analysis further support that, if successfully replicated in population-level programmes, lifestyle interventions in people with impaired glucose tolerance could reduce the massive and growing burden of preventable disease from type 2 diabetes and its cardiovascular sequelae. It acknowledges that the study has undoubted limitations:
• Study size is small by modern standards• Follow-up analysis should be considered observational in nature.• Study population was defined by glucose concentrations from an oral glucose tolerance test based on older criteria different from modern definitions of prediabetes or with diagnostic criteria based on HbA1c. • Asian origin of the population introduces some uncertainty over wider generalisability,• Questions might remain over whether interventions should be triggered by impaired fasting glucose, stimulated blood glucose, or indeed HbA1c, which is now the most widely used test. HbA1c is a marker of cardiovascular risk even at subdiabetic levels, and has effects beyond glycaemia that can also be improved by other diet and lifestyle factors.
It adds both the understanding of the pathophysiology of type 2 diabetes, and the entire paradigm for its management, are undergoing radical changes. Putting together the results of the Da Qing study and other very consistent diabetes prevention trials with findings from recent intensive weight-management interventions, it is clear that type 2 diabetes should no longer be considered an endocrine disease, but a primary nutritional disease, part of a constellation of conditions that are caused quite specifically by weight gain when, in genetically susceptible individuals, excess body fat starts to accumulate in organs crucial to metabolic control and interferes with organ function. It concludes that the challenge now is for health-care services and public health policies to act on a large scale on the new understanding of type 2 diabetes, with the dual aims of population-directed primary prevention and effective treatment programmes targeting remission.