Table 1 Demographic characteristics of samples

Sample size (N)

5870

6165

5955

6777

6439

6286

6121

5287

Age

36.83 (28.36,44.69)

38.09 (29.56,46.22)

39.99 (31.21,47.69)

41.54 (33.14,49.03)

43.27 (35.24,51.30)

44.05 (36.70,52.13)

45.61 (38.08,53.11)

47.13 (39.89,54.09)

<0.01

Education level (%)

<0.01

None/primary/junior middle school

97.94

98.27

97.95

96.05

95.99

94.45

94.47

91.88

Senior school

2.00

1.68

2.03

3.89

4.00

5.53

5.48

7.88

College and above

0.07

0.05

0.02

0.06

0.02

0.02

0.05

0.25

Income tertile

0.85

Low income

34.49

33.40

33.82

33.18

33.33

33.20

32.99

33.63

Middle income

32.93

33.24

32.99

33.78

33.69

33.63

33.36

33.05

High income

32.58

33.36

33.19

33.03

32.98

33.17

33.66

33.32

Energy intake (1000 kcal/day)

24.47 (19.94,29.05)

23.75 (19.63,28.36)

24.54 (20.44,29.63)

23.56 (19.28,28.17)

22.76 (18.61,27.68)

22.98 (18.64,28.40)

21.80 (17.88,26.39)

20.77 (16.48,25.79)

<0.01

Total physical activity (METs/d)

60.86 (31.48,90.68)

51.77 (28.57,80.57)

50.66 (27.40,77.15)

43.57 (19.89,68.57)

32.95 (14.77,59.00)

33.20 (15.14,57.35)

32.29 (15.59,56.96)

31.05 (15.79,55.71)

<0.01

Sedentary time (hours/d)

-

-

-

-

2.00 (1.33,3.50)

2.00 (1.50,3.30)

2.29 (1.64,3.57)

2.14 (1.65,3.29)

<0.01

Urbanization index

43.92 (31.91,60.57)

45.21 (33.37,62.54)

51.12 (35.18,66.90)

55.19 (42.93,76.76)

58.75 (44.51,81.63)

62.24 (47.41,82.48)

64.09 (50.86,84.69)

68.05 (52.25,86.54)

<0.01

BMI (kg/m²)

21.28 (19.74,23.16)

21.52 (19.95,23.47)

21.91 (20.20,24.09)

22.54 (20.63,24.84)

22.81 (20.76,25.16)

22.90 (20.99,25.29)

23.22 (21.13,25.61)

23.55 (21.40,25.97)

<0.01