Covariate assessments

Trained investigators conducted the face-to-face interviews at baseline and each follow-up visit. We collected information on demographic characteristics (e.g., age, sex, household income and education level), lifestyles (e.g., smoking status, alcohol drinking and tea drinking), chronic disease history and medication use. Physical activity, including exercise, leisure-time activity, housework and occupation-related activity, and other daily activities, was estimated using a 19-item questionnaire and metabolic equivalent·h/d [34]. A validated 79-item food frequency questionnaire was used to estimate the habitual dietary intakes during the past year [35]. Energy intake was calculated according to the Chinese Food Composition Table 2004 [36].

Anthropometric measurements and blood pressure were measured by trained project members using the same method and equipment at baseline and each follow-up visit. When participants took off shoes and wore light clothing, height and weight were measured with an accuracy of 0.1 cm for height and 0.1 kg for weight. When participants stood erect, waist circumference and hip circumference were measured to the nearest 0.1 cm. Blood pressure was measured on the left arm with a mercury sphygmomanometer after participants had seated comfortably for at least 10 min. All indexes were measured twice, and the averages of all the readings were calculated for data analyses. Body mass index (BMI) was calculated as weight (kg) divided by the square of height (m²). The ratio of waist to hip circumference (WHR) was equal to waist circumference (cm) divided by hip circumference (cm). Abdominal obesity was defined as waist-hip ratio ≥ 0.90 cm for men or ≥ 0.85 cm for women [37]. Hypertension was defined as self-reported hypertension medications, systolic blood pressure (SBP) ≥ 140 mmHg or diastolic blood pressure (DBP) ≥ 90 mmHg [38].