Basic Characteristics of the Study population
A total of 25528 participants were included in the study with an average age of 59.1 years. Among these, 13067 (44.1% males) were urban residents and 12461 (46.6% males) were rural residents. There were significant differences between urban and rural participants regarding age, gender, marital status, education, smoking, alcohol, physical activity, and income. BMI, WC, TC, TG, and FPG were higher in urban than in rural participants (P < 0.001), whereas HDL-C was the opposite (P < 0.001, Table 1). Table 2 shows that the prevalence of MetS in urban areas was32.4%, higher than that in rural 24.7% (P < 0.001).
Table 1 Basic characteristics of the study population in urban and rural
|
Total
|
Urban
|
Rural
|
p-Value
|
N
|
25528
|
13067
|
12461
|
|
Age, years
|
59.1 (59.0, 59.2)
|
59.7 (59.5, 59.8)
|
58.5 (58.3, 58.7)
|
<0.001
|
Gender, n (%)
|
|
|
|
|
Male
|
11574 (45.3)
|
5762 (44.1)
|
5812 (46.6)
|
|
Female
|
13954 (54.7)
|
7305 (55.9)
|
6649 (53.4)
|
|
Marital status, n (%)
|
|
|
|
0.011
|
Single
|
181 (0.7)
|
84 (0.6)
|
97 (0.8)
|
|
Married
|
23093 (90.5)
|
11767 (90.1)
|
11326 (90.9)
|
|
Divorced or Widowed
|
2254 (8.8)
|
1216 (9.3)
|
1038 (8.3)
|
|
Education, n (%)
|
|
|
|
<0.001
|
Primary schools or below
|
12407 (48.6)
|
4426 (33.9)
|
7981 (64.1)
|
|
Junior high school
|
7980 (31.3)
|
4556 (34.9)
|
3424 (27.5)
|
|
Senior high school
|
3963 (15.5)
|
2975 (22.8)
|
988 (7.9)
|
|
College or above
|
1178 (4.6)
|
1110 (8.5)
|
68 (0.6)
|
|
Smoking, n (%)
|
|
|
|
<0.001
|
Ever/Never
|
6830 (26.8)
|
3065 (23.5)
|
3765 (30.2)
|
|
Current
|
18698 (73.2)
|
10002 (76.5)
|
8696 (69.8)
|
|
Alcohol, n (%)
|
|
|
|
<0.001
|
Ever/Never
|
8169 (32.0)
|
4189 (32.1)
|
3980 (31.9)
|
|
Current
|
17359 (68.0)
|
8878 (67.9)
|
8481 (68.1)
|
|
Physical activity, n (%)
|
|
|
|
<0.001
|
Yes
|
4012 (15.7)
|
3309 (25.3)
|
703 (5.6)
|
|
No
|
21516 (84.3)
|
9758 (74.7)
|
11758 (94.4)
|
|
Income, n (%)
|
|
|
|
<0.001
|
Low
|
11940 (46.8)
|
7024 (53.8)
|
4916 (39.5)
|
|
Middle
|
5202 (20.4)
|
1833 (14.0)
|
3369 (27.0)
|
|
High
|
7276 (28.5)
|
3456 (26.5)
|
3820 (30.7)
|
|
Unanswered
|
1110 (4.4)
|
754 (5.8)
|
356 (2.9)
|
|
BMI, kg/m2
|
24.1 (24.1, 24.2)
|
24.6 (24.6, 24.7)
|
23.6 (23.6, 23.7)
|
<0.001
|
WC, cm
|
82.9 (82.7, 83.0)
|
84.2 (84.0, 84.3)
|
81.5 (81.3, 81.6)
|
<0.001
|
SBP, mmHg
|
130.9 (130.6, 131.1)
|
130.7 (130.4, 131.1)
|
131.0 (130.6, 131.4)
|
0.640
|
DBP, mmHg
|
81.0 (80.8, 81.1)
|
80.9 (80.7, 81.1)
|
81.1 (81.9, 81.3)
|
0.929
|
TC, mmol/L
|
4.79 (4.78, 4.80)
|
4.89 (4.87, 4.90)
|
4.70 (4.68, 4.72)
|
<0.001
|
HDL-C, mmol/L
|
1.19 (1.19, 1.20)
|
1.18 (1.18, 1.19)
|
1.20 (1.20, 1.21)
|
<0.001
|
TG, mmol/L
|
1.50 (1.49, 1.51)
|
1.55 (1.53, 1.57)
|
1.44 (1.42, 1.46)
|
<0.001
|
FPG, mmol/L
|
5.52 (5.50, 5.54)
|
5.67 (5.64, 5.69)
|
5.36 (5.34, 5.39)
|
<0.001
|
Mean value (95% confidence interval) or n (%) were shown; BMI, body mass index; WC, waist circumference; SBP, systolic blood pressure; DBP, diastolic blood pressure; TC, total cholesterol; HDL-C, high-density lipoprotein cholesterol; TG, triglyceride; FPG, fasting plasma glucose
Table 2 Basic characteristics of normal and MetS in urban and rural
|
Urban
|
|
Rural
|
p-Value
|
|
Normal
|
MetS
|
|
Normal
|
MetS
|
Case, n (%)
|
8830 (67.6)
|
4237 (32.4)
|
|
9388 (75.3)
|
3073 (24.7)
|
<0.001
|
Age, n (%)
|
|
|
|
|
|
<0.001
|
45-59 years
|
5078 (57.5)
|
2004 (47.3)
|
|
5598 (59.6)
|
1702 (55.4)
|
|
60-74 years
|
3353 (38.0)
|
1997 (47.1)
|
|
3420 (36.4)
|
1247 (40.6)
|
|
75- years
|
399 (4.5)
|
236 (5.6)
|
|
370 (3.9)
|
124 (4.0)
|
|
Gender, n (%)
|
|
|
|
|
|
0.248
|
Male
|
3788 (42.9)
|
1974 (46.6)
|
|
4526 (48.2)
|
1286 (41.9)
|
|
Female
|
5042 (57.1)
|
2263 (53.4)
|
|
4862 (51.8)
|
1787 (58.2)
|
|
Marital status, n (%)
|
|
|
|
|
|
0.246
|
Single
|
63 (0.7)
|
21 (0.5)
|
|
88 (0.9)
|
9 (0.3)
|
|
Married
|
7956 (90.1)
|
3811 (90.0)
|
|
5811 (90.7)
|
2815 (91.6)
|
|
Divorced or Widowed
|
811 (9.2)
|
405 (9.6)
|
|
789 (8.4)
|
249 (8.1)
|
|
Education, n (%)
|
|
|
|
|
|
<0.001
|
Primary schools or below
|
3022 (34.2)
|
1404 (33.1)
|
|
6092 (64.9)
|
1889 (61.5)
|
|
Junior high school
|
3062 (34.7)
|
1494 (35.3)
|
|
2546 (27.1)
|
878 (28.6)
|
|
Senior high school
|
2035 (23.1)
|
940 (22.2)
|
|
709 (7.6)
|
279 (9.1)
|
|
College or above
|
711 (8.1)
|
399 (9.4)
|
|
41 (0.4)
|
27 (0.9)
|
|
Smoking, n (%)
|
|
|
|
|
|
<0.001
|
Ever/Never
|
6725 (76.2)
|
3277 (77.3)
|
|
6248 (66.6)
|
2233 (72.7)
|
|
Current
|
2105 (23.8)
|
960 (22.7)
|
|
3140 (33.4)
|
840 (27.3)
|
|
Alcohol, n (%)
|
|
|
|
|
|
<0.001
|
Ever/Never
|
5926 (67.1)
|
2952 (69.7)
|
|
6374 (67.9)
|
2322 (75.6)
|
|
Current
|
2904 (32.9)
|
1285 (30.3)
|
|
3014 (32.1)
|
751 (24.4)
|
|
Physical activity, n (%)
|
|
|
|
|
|
<0.001
|
Yes
|
2149 (24.3)
|
1160 (27.4)
|
|
460 (4.9)
|
243 (7.9)
|
|
No
|
6681 (75.7)
|
3077 (72.6)
|
|
8928 (95.1)
|
2830 (92.1)
|
|
Income, n (%)
|
|
|
|
|
|
0.004
|
Low
|
4835 (54.8)
|
2189 (51.7)
|
|
3713 (39.6)
|
1203 (39.2)
|
|
Middle
|
1195 (13.5)
|
638 (15.1)
|
|
2594 (27.6)
|
775 (25.2)
|
|
High
|
2273 (25.7)
|
1183 (27.9)
|
|
2819 (30.0)
|
1001 (32.6)
|
|
Unanswered
|
527 (6.0)
|
227 (5.4)
|
|
262 (2.8)
|
94 (3.1)
|
|
Dietary Fructose Intake Level and Food Sources
The average daily dietary total fructose intake for urban residents was 11.6g and 7.6g for rural residents. Dietary total fructose intake level was significantly higher in urban residents than that in rural residents, as well as free-fructose and bound-fructose levels (P < 0.001). Intakes of protein and fat were significantly higher in urban residents while energy and carbohydrate were higher in rural residents (P < 0.001). Table 3 shows the basic characteristics of dietary fructose and nutrients with mean and quartiles.
Table 3 Intake status of dietary fructose and nutrients in urban and rural residents
|
City
|
|
Rural
|
p-Value
|
|
Mean
|
P25th
|
Median
|
P75th
|
|
Mean
|
P25th
|
Median
|
P75th
|
Total Fructose, g/d
|
11.6
|
4.8
|
8.3
|
14.5
|
|
7.6
|
3.4
|
5.3
|
8.8
|
<0.001
|
Free-Fructose, g/d
|
6.7
|
2.2
|
4.2
|
8.4
|
|
4.6
|
1.6
|
2.7
|
5.1
|
<0.001
|
Bound-Fructose, g/d
|
4.9
|
2.4
|
3.7
|
6.0
|
|
3.1
|
1.6
|
2.4
|
3.7
|
<0.001
|
Energy, kcal/d
|
1887
|
1454
|
1780
|
2204
|
|
2159
|
1648
|
2041
|
2547
|
<0.001
|
Protein, g/d
|
61.2
|
44.8
|
56.6
|
72.5
|
|
59.3
|
43.6
|
55.4
|
71.2
|
<0.001
|
Fat, g/d
|
76.1
|
50.2
|
69.2
|
94.1
|
|
70.8
|
44.0
|
64.0
|
90.2
|
<0.001
|
Carbohydrate, g/d
|
240.3
|
178.0
|
224.9
|
284.3
|
|
322.7
|
238.7
|
299.4
|
378.7
|
<0.001
|
We further investigated the food sources of dietary fructose. Fruits and fruit products, vegetables and vegetable products, and snacks were the top three food sources for dietary fructose among urban residents accounting 69.02% for the total dietary fructose intake, while vegetables and vegetable products, Fruits and fruit products, and grain and grain products were the top three food sources for dietary fructose in rural residents contributing 73.45% to the total dietary fructose intake (Figure 1). Food sources of total dietary fructose in urban and rural areas with mean and quartiles were shown in table S1.
The Association between Dietary Fructose Intake and Risk of MetS
For urban residents, in addition to FPG, there were significant differences in WC, SBP, DBP, TG and HDL-C between the quartiles. The prevalence of MetS was higher in the third quartile than that in the first and forth quartiles (P < 0.05). For rural residents, we found significant differences in FPG, SBP, DBP, TG, and HDL-C between the quartiles except for WC. There was no significant difference in the prevalence of MetS between quartiles (Table 4).
Table 4 Basic characteristics of components of MetS by the quartiles of dietary fructose intake
|
Q1
|
Q2
|
Q3
|
Q4
|
p-Value
|
Urban
|
3266
|
3268
|
3266
|
3267
|
|
Dietary fructose
|
3.4 (3.4, 3.4)
|
6.4 (6.4, 6.4)
|
11.1 (11.1, 11.1)
|
25.6 (25.1, 26.2)
|
|
WC, cm
|
83.5 (83.2, 83.8)
|
84.5 (84.1, 84.8)1
|
84.4 (84.1, 84.8) 1
|
84.3 (83.9, 84.6) 1
|
<0.001
|
FPG, mmol/L
|
5.68 (5.63, 5.73)
|
5.72 (5.67, 5.78)
|
5.64 (5.59, 5.69)
|
5.62 (5.57, 5.67)
|
0.081
|
SBP, mmHg
|
131.8 (131.1, 132.5)
|
132.0 (131.3, 132.7)
|
130.3 (129.7, 131.0) 1,2
|
128.8 (128.2, 129.4) 1,2,3
|
<0.001
|
DBP, mmHg
|
81.0 (80.6, 81.4)
|
81.5 (81.2, 81.9)
|
80.8 (80.5, 81.2)
|
80.2 (79.9, 80.6) 1,2
|
<0.001
|
TG, mmol/L
|
1.49 (1.46, 1.53)
|
1.56 (1.53, 1.60) 1
|
1.59 (1.55, 1.62) 1
|
1.56 (1.53, 1.60)
|
0.002
|
HDL-C, mmol/L
|
1.20 (1.19, 1.22)
|
1.19 (1.18, 1.20)
|
1.18 (1.16, 1.18) 1
|
1.17 (1.16, 1.18) 1
|
<0.000
|
MetS, n (%)
|
1019 (31.2)
|
1083 (33.1)
|
1109 (34.0)1
|
1027 (31.4)3
|
0.048
|
Rural
|
3115
|
3116
|
3115
|
3115
|
|
Dietary fructose
|
2.5 (2.5, 2.5)
|
4.3 (4.3, 4.3)
|
6.8 (6.8, 6.8)
|
16.8 (16.4, 17.2)
|
|
WC, cm
|
81.1 (80.7, 81.4)
|
81.5 (81.1, 81.8)
|
81.7 (81.3, 82.1)
|
81.6 (81.3, 81.9)
|
0.087
|
FPG, mmol/L
|
5.37 (5.32, 5.42)
|
5.44 (5.39, 5.49)
|
5.32 (5.28, 5.37)2
|
5.32 (5.27, 5.37) 2
|
0.001
|
SBP, mmHg
|
132.6 (131.9, 133.4)
|
131.2 (130.5, 131.9)1
|
130.9 (130.2, 131.7) 1
|
129.3 (128.5, 130.0) 1,2,3
|
<0.001
|
DBP, mmHg
|
81.6 (81.2, 82.0)
|
81.0 (80.6, 81.4)
|
81.0 (80.6, 81.4)
|
80.7 (80.3, 81.1) 1
|
0.017
|
TG, mmol/L
|
1.39 (1.35, 1.42)
|
1.43 (1.39, 1.47)
|
1.43 (1.39, 1.47)
|
1.52 (1.48, 1.57) 1,2,3
|
<0.001
|
HDL-C, mmol/L
|
1.22 (1.21, 1.24)
|
1.22 (1.21, 1.23)
|
1.20 (1.18, 1.21) 1,2
|
1.18 (1.16, 1.19) 1,2
|
<0.001
|
MetS, n (%)
|
764 (24.5)
|
772 (24.8)
|
805 (25.8)
|
732 (23.5)
|
0.199
|
1: compared with Q1, p < 0.05; 2: compared with Q2, p < 0.05; 3: compared with Q3, p < 0.05
Compared with the first quartile, the risk of MetS was increased in the third quartile among urban residents (OR: 1.13; 95%CI: 1.02-1.26). After adjusting confounding factors (gender, age, education, marital status, smoking, alcohol, physical activity, income, energy, protein, fat, carbohydrate, TC and BMI), no statistical significance was found. For rural residents, regardless of adjustments made for confounding factors, no association between dietary fructose intake and the risk of MetS was found (Table 5).
Table 5 The association between dietary fructose intake and risk of MetS
|
Dietary fructose intake
|
p-Value
|
|
Q1
|
Q2
|
Q3
|
Q4
|
Urban
|
|
|
|
|
|
Mode1
|
1.00
|
1.09 (0.98, 1.21)
|
1.13 (1.02, 1.26)
|
1.01 (0.91, 1.12)
|
0.048
|
Mode2
|
1.00
|
1.08 (0.97, 1.20)
|
1.10 (0.99, 1.22)
|
0.97 (0.87, 1.09)
|
0.059
|
Mode3
|
1.00
|
1.03 (0.92, 1.16)
|
1.07 (0.95, 1.21)
|
0.96 (0.85, 1.10)
|
0.315
|
Rural
|
|
|
|
|
|
Mode1
|
1.00
|
1.01 (0.90, 1.14)
|
1.07 (0.96, 1.20)
|
0.95 (0.84, 1.06)
|
0.199
|
Mode2
|
1.00
|
1.04 (0.95, 1.17)
|
1.15 (1.02, 1.29)
|
1.06 (0.93, 1.19)
|
0.148
|
Mode3
|
1.00
|
1.03 (0.90, 1.18)
|
1.14 (1.00, 1.31)
|
1.03 (0.90, 1.19)
|
0.230
|
Mode1: crude; Mode2: adjusted gender, age, education, marital status, smoking, alcohol, physical activity, income, energy, protein, fat, carbohydrate, TC; Mode3: mode2 plus BMI.
Stratified analysis of the Association between Dietary Fructose Intake and Risk of MetS
We further analyzed the association between dietary fructose intake and the risk of MetS stratified by gender, physical activity, smoking, and alcohol use. For urban residents with physical activities, the prevalence, and the risk of MetS decreased with the increase of the quartile levels of dietary fructose intake (P < 0.001). Compared with the first quartile, the risk of MetS in the fourth quartile (OR: 0.67; 95%CI: 0.52-0.86) was reduced after adjustment for confounding factors (Table 6). In the sensitivity analysis, we also found a significant reduction in the risk of MetS in the fourth quartile (OR, 95%CI: 0.67, 0.51-0.89; 0.63, 0.46-0.85; 0.74, 0.56-0.98) compared with the first quartile when excluding smokers, alcohol users, and BMI < 18.5 or BMI ≥ 28, respectively (Table 7). For urban residents with no physical activities, the prevalence of MetS increased with the increase of dietary fructose intake (P = 0.007). There was no significant difference for the relationship between dietary fructose intake and the risk of MetS after multivariate adjustment, as was the case in the sensitivity analysis (Table 6, Table 7).
Table 6 Stratified analysis of the association between dietary fructose intake and risk of MetS by physical activity in urban residents
|
Dietary fructose intake
|
p-Value
|
|
Q1
|
Q2
|
Q3
|
Q4
|
Physical activity
|
|
|
|
|
|
MetS, n (%)
|
233 (42.1)
|
236 (36.2)
|
324 (35.9)
|
367 (30.6)
|
<0.001
|
Mode1
|
1.00
|
0.78 (0.62, 0.99)
|
0.77 (0.62, 0.96)
|
0.61 (0.49, 0.75)
|
<0.001
|
Mode2
|
1.00
|
0.79 (0.63, 1.01)
|
0.79 (0.63, 0.99)
|
0.64 (0.51, 0.80)
|
0.001
|
Mode3
|
1.00
|
0.79 (0.61, 1.03)
|
0.81 (0.62, 1.04)
|
0.67 (0.52, 0.86)
|
0.016
|
Non-physical activity
|
|
|
|
|
|
MetS, n (%)
|
786 (29.0)
|
846 (32.3)
|
785 (33.2)
|
660 (32.0)
|
0.007
|
Mode1
|
1.00
|
1.17 (1.04, 1.32)
|
1.22 (1.08, 1.37)
|
1.15 (1.02, 1.30)
|
0.007
|
Mode2
|
1.00
|
1.15 (1.02, 1.30)
|
1.17 (1.04, 1.33)
|
1.09 (0.95, 1.25)
|
0.046
|
Mode3
|
1.00
|
1.01 (0.96, 1.26)
|
1.14 (0.99, 1.32)
|
1.07 (0.92, 1.25)
|
0.276
|
Mode1: crude; Mode2: adjusted gender, age, education, marital status, smoking, alcohol, income, energy, protein, fat, carbohydrate, TC; Mode3: mode2 plus BMI.
Table 7 Sensitivity analysis of the association between dietary fructose intake and risk of MetS by physical activity in urban residents
|
Dietary fructose intake
|
p-Value
|
|
Q1
|
Q2
|
Q3
|
Q4
|
Physical activity
|
|
|
|
|
|
MetS, n (%)*
|
188 (41.3)
|
185 (34.9)
|
256 (35.1)
|
313 (30.1)
|
<0.001
|
Mode1*
|
1.00
|
0.76 (0.59, 0.99)
|
0.77 (0.60, 0.98)
|
0.61 (0.49, 0.77)
|
<0.001
|
Mode2*
|
1.00
|
0.78 (0.60, 1.02)
|
0.79 (0.61, 1.01)
|
0.63 (0.49, 0.81)
|
0.004
|
Mode3*
|
1.00
|
0.77 (0.57, 1.03)
|
0.81 (0.62, 1.07)
|
0.67 (0.51, 0.89)
|
0.039
|
MetS, n (%)#
|
168 (42.5)
|
166 (37.8)
|
207 (34.2)
|
230 (30.1)
|
<0.001
|
Mode1#
|
1.00
|
0.82 (0.62, 1.08)
|
0.70 (0.54, 0.91)
|
0.58 (0.45, 0.75)
|
<0.001
|
Mode2#
|
1.00
|
0.83 (0.63, 1.11)
|
0.70 (0.53, 0.91)
|
0.58 (0.44, 0.76)
|
0.001
|
Mode3#
|
1.00
|
0.86 (0.63, 1.17)
|
0.73 (0.54, 0.99)
|
0.63 (0.46, 0.85)
|
0.019
|
MetS, n (%)$
|
147 (33.2)
|
166 (30.8)
|
234 (31.0)
|
268 (26.0)
|
0.017
|
Mode1$
|
1.00
|
0.90 (0.69, 1.17)
|
0.90 (0.70, 1.16)
|
0.71 (0.56, 0.90)
|
0.017
|
Mode2$
|
1.00
|
0.84 (0.63, 1.11)
|
0.70 (0.53, 0.91)
|
0.58 (0.44, 0.76)
|
0.001
|
Mode3$
|
1.00
|
0.89 (0.66, 1.19)
|
0.92 (0.70, 1.22)
|
0.74 (0.56, 0.98)
|
0.119
|
Non- physical activity
|
|
|
|
|
|
MetS, n (%)*
|
602 (29.6)
|
650 (34.36)
|
590 (33.50)
|
493 (31.58)
|
0.008
|
Mode1*
|
1.00
|
1.25 (1.09, 1.42)
|
1.20 (1.05, 1.38)
|
1.10 (0.95, 1.27)
|
0.008
|
Mode2*
|
1.00
|
1.22 (1.07, 1.40)
|
1.16 (1.01, 1.34)
|
1.06 (0.90, 1.24)
|
0.020
|
Mode3*
|
1.00
|
1.15 (0.99, 1.34)
|
1.14 (0.97, 1.34)
|
1.06 (0.89, 1.26)
|
0.231
|
MetS, n (%)#
|
602 (31.1)
|
620 (34.0)
|
542 (33.8)
|
417 (31.8)
|
0.182
|
Mode1#
|
1.00
|
1.14 (0.99, 1.31)
|
1.13 (0.98, 1.30)
|
1.03 (0.89, 1.20)
|
0.182
|
Mode2#
|
1.00
|
1.12 (0.98, 1.29)
|
1.08 (0.93, 1.25)
|
0.98 (0.83, 1.15)
|
0.210
|
Mode3#
|
1.00
|
1.07 (0.92, 1.26)
|
1.06 (0.89, 1.25)
|
0.95 (0.79, 1.14)
|
0.511
|
MetS, n (%)$
|
541 (24.3)
|
572 (27.0)
|
534 (27.6)
|
450 (26.3)
|
0.073
|
Mode1$
|
1.00
|
1.16 (1.01, 1.33)
|
1.19 (1.03, 1.37)
|
1.12 (0.97, 1.29)
|
0.073
|
Mode2$
|
1.00
|
1.12 (0.98, 1.29)
|
1.08 (0.93, 1.25)
|
0.98 (0.83, 1.15)
|
0.210
|
Mode3$
|
1.00
|
1.12 (0.96, 1.30)
|
1.12 (0.96, 1.32)
|
1.04 (0.88, 1.24)
|
0.380
|
Mode1: crude; Mode2: adjusted gender, age, education, marital status, smoking, alcohol, income, energy, protein, fat, carbohydrate, TC; Mode3: mode2 plus BMI. * excluded smokers; # excluded alcohol; $ excluded BMI<18.5, and BMI≥28.
Regardless of physical activities for rural residents, there was no association between dietary fructose intake and the risk of MetS (Table S2). When stratified by gender, the prevalence of MetS was the lowest in the first quartile of dietary fructose intake for urban males, but in the fourth quartile for urban females (Table S3). There was no association between dietary fructose intake and the risk of MetS after multivariate adjustment stratified by gender, smoking and alcohol (Table S3, Table S4, Table S5).