Figure 1Distribution of propensity scores among participants with lower and higher plasma calcium levels. Lower calcium, plasma calcium <2.37 mmol/L; higher calcium, plasma calcium ≥2.37 mmol/L.
Figure 2Kaplan-Meier estimates of cumulative incidence of hypertension.
Figure 3Development of hypertension among participants with higher and lower levels of plasma calcium according to quartiles of dietary calcium intake. Dietary calcium intake quartiles: Q1, <301; Q2, 302−432; Q3, 433−604; Q4, ≥605 mg/d.
Table 1Baseline characteristics of participants before and after propensity score matchinga
Characteristics |
Before matching (n = 5560)
|
After matching (n = 4306)
|
Lower calciumb
|
Higher calciumc
|
p
|
Lower calciumb
|
Higher calciumc
|
p
|
Age, years |
50.5 ± 8.7 |
51.5 ± 8.5 |
<0.001 |
51.1 ± 0.2 |
51.0 ± 0.2 |
0.724 |
Smoking, n (%) |
|
|
0.027 |
|
|
0.514 |
Never |
1619 (56.5) |
1603 (59.4) |
|
1300 (60.4) |
1279 (59.4) |
|
Ever |
1245 (43.5) |
1093 (40.5) |
|
853 (39.6) |
874 (40.6) |
|
Area, n (%) |
|
|
0.254 |
|
|
0.170 |
Ansung (rural) |
1403 (49.0) |
1362 (50.5) |
|
1092 (50.7) |
1047 (48.6) |
|
Ansan (urban) |
1461 (51.0) |
1334 (49.5) |
|
1061 (49.3) |
1106 (51.4) |
|
Plasma calcium, mmol/L |
2.26 ± 0.0 |
2.45 ± 0.0 |
<0.001 |
2.27 ± 0.0 |
2.45 ± 0.0 |
<0.001 |
Systolic BP, mmHg |
113.9 ± 0.2 |
114.9 ± 0.2 |
<0.001 |
114.5 ± 0.2 |
114.6 ± 0.2 |
0.675 |
Serum creatinine, μmol/L |
87.0 ± 11.3 |
88.1 ± 5.7 |
<0.001 |
87.0 ± 11.3 |
87.7 ± 5.0 |
0.006 |
Microalbuminuria, n (%) |
102 (3.6) |
228 (8.5) |
<0.001 |
100 (4.6) |
103 (4.8) |
0.829 |
Serum glucose, mmol/L |
4.72 ± 0.02 |
4.61 ± 0.03 |
0.002 |
4.59 ± 0.03 |
4.64 ± 0.03 |
0.212 |
BMI, kg/m2
|
24.6 ± 0.1 |
24.4 ± 0.1 |
0.011 |
24.5 ± 0.1 |
24.5 ± 0.1 |
0.810 |
Total cholesterol, mmol/L |
4.93 ± 0.02 |
4.88 ± 0.02 |
0.031 |
4.87 ± 0.02 |
4.89 ± 0.02 |
0.554 |
HDL-C, mmol/L |
1.18 ± 0.0 |
1.13 ± 0.0 |
<0.001 |
1.17 ± 0.01 |
1.14 ± 0.01 |
<0.001 |
Triacylglyceride, mmol/L |
3.68 ± 0.04 |
4.35 ± 0.05 |
<0.001 |
3.82 ± 0.05 |
4.25 ± 0.06 |
<0.001 |
GTP, U/L |
29.4 ± 0.9 |
33.8 ± 1.2 |
0.003 |
30.3 ± 1.1 |
30.7 ± 1.0 |
0.813 |
Table 2Multivariable adjusted hazard ratios for hypertension with higher plasma calciuma before and after propensity score matching
|
No. cases/total |
Person-years |
Unadjusted
|
Adjustedb
|
HR (95%CI) |
p
|
HR (95%CI) |
p
|
Before matching |
1016/5560 |
25,810 |
1.42 (1.25−1.61) |
<0.001 |
1.29 (1.14−1.47) |
<0.001 |
After matchingc
|
776/4306 |
20,016 |
1.24 (1.07−1.42) |
0.003 |
1.24 (1.07−1.43) |
0.004 |