Cohort profile: The Japan diabetes complications study: a long-term follow-up of a randomised lifestyle intervention study of type 2 diabetes.

The Japan Diabetes Complications Study, a randomised lifestyle intervention study of type 2 diabetes conducted at 59 institutes throughout Japan that enrolled 2033 eligible patients from January 1995 to March 1996, was directed at: (i) determining the incidence and progression rates of complications of diabetes; (ii) exploring clinical risk factors for complications of diabetes; and (iii) determining the association between lifestyle factors, including diet and physical activity, and complications of diabetes, in addition to comparing, in a randomised manner, the effects on type 2 diabetes of an extensive lifestyle intervention and conventional treatment. The protocol for the study originally specified four study populations according to primary outcomes, consisting of: (1) a macroangiopathy group (N = 1771); (ii) a nephropathy group (N = 1607); (iii) a retinopathy-incident group (N = 1221); and (iv) a retinopathy-progression group (N = 410). The primary outcomes were: (i) development of retinopathy; (ii) progression of retinopathy; (iii) development of overt nephropathy; and (iv) occurrence of macroangiopathic events including proven coronary heart disease and stroke. The study was originally planned to follow patients for 8 years, and an extended follow-up is ongoing. Information about primary outcomes, laboratory tests, and other clinical variables for each patient was collected at a central data centre through an annual report from each investigator. Additionally, extensive lifestyle surveys were conducted at baseline and 5 years after the beginning of the study intervention in both the intervention and conventional treatment groups. A description of the occurrence of complications of diabetes and of all-cause mortality, provided in this paper, demonstrated a clear gender-based difference in cardiovascular disease and all-cause mortality.