2.2. Ascertainment of diabetes and age at diagnosis

The baseline diabetes status was defined by at least one of the following criteria: (1) self-reported history of diabetes or reported a diagnosis of diabetes by a doctor; (2) hospital diagnosis of diabetes by the International Classification of Diseases, Ninth Revision (ICD-9: 250) and Tenth Revision (ICD-10: E10-E14); (3) use of diabetes medications or insulin; (4) glycosylated hemoglobin (HbA1c) levels ≥48 mmol/mol (20). The diagnosis age of diabetes can be directly obtained through self-reported age of diagnosis, inpatient records. For diabetes diagnosed only by HbA1c, the age of diabetes diagnosis was the baseline age. Those without the age of diabetes diagnosis were considered missing (1,644 individuals).