*2.4. Covariates*

Information on sociodemographic characteristics, lifestyle behaviors, and personal health and medical history were collected in the CHNS. Baseline age, gender, living region, residency, education level, per capita household income, smoking status, alcohol consumption, physical activity, body mass index (BMI), and medical history (cancer, hypertension, diabetes, stroke, and myocardial infarction) were obtained from the phase at entry.

Per capita household income was estimated at each phase, and missing values for per capita household income was replaced by the medians of each survey site. Income was grouped into tertiles and was labeled as low, middle, and high at each phase. Physical activity was measured in terms of metabolic equivalent of task (MET)-hours per week [24]. Missing values for height and weight were replaced by the means of two adjacent surveys. BMI was computed as weight (kg)/(height (m))2. Since blood pressure was measured, participants who had been previously diagnosed with hypertension or with systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg were all regarded as hypertensive patients. Other medical histories were based on the self-report from participants. Comorbidity was defined as having at least one of the four diseases (hypertension, diabetes, stroke, and myocardial infarction) at the baseline survey.
