Table 4.

Association between Cu/Zn ratio and knee chondrocalcinosis (n = 12,362)

	Tertiles of Cu/Zn ratio			P for trend
	1 (≤ 1.07)	2 (1.08–1.38)	3 (≥ 1.39)
Total
Knee chondrocalcinosis (%)	0.7	1.0	2.1	–
N for kneea	8158	8406	8157	–
Model 1 (95% CI)	1.00 (reference)	1.02 (0.61, 1.69)	2.23 (1.38, 3.59)	< 0.001
Model 2 (95% CI)	1.00 (reference)	1.00 (0.60, 1.67)	2.12 (1.31, 3.42)	< 0.001
Model 3 (95% CI)	1.00 (reference)	1.03 (0.62, 1.72)	2.27 (1.40, 3.68)	< 0.001
Model 4 (95% CI)	1.00 (reference)	1.03 (0.62, 1.71)	2.26 (1.41, 3.63)	< 0.001
Model 5 (95% CI)	1.00 (reference)	1.01 (0.61, 1.68)	2.20 (1.36, 3.55)	< 0.001

Model 1 included age (40–49, 50–59, 60–69, ≥ 70 years), body mass index (< 28, ≥ 28 kg/m²) and sex (n = 12,362);

Model 2 added serum iron (tertiles) on the basis of model 1 (n = 12,357);

Model 3 added serum calcium (tertiles) on the basis of model 1 (n = 12,264);

Model 4 added serum magnesium (tertiles) on the basis of model 1 (n = 12,362);

Model 5 added serum phosphorus (tertiles) on the basis of model 1 (n = 12,264)

^aThree right knees with K-L 4 grade were excluded for analysis (data from the contralateral knees were retained)

N number, CI confidence interval, Cu/Zn ratio the ratio of serum copper to zinc concentrations