Table 3.

Association between serum copper and knee chondrocalcinosis (n = 12,362)

	Tertiles of serum copper (μmol/L)			P for trend
	1 (≤ 14.7)	2 (14.8–17.5)	3 (≥ 17.6)
Total
Knee chondrocalcinosis (%)	0.8	1.1	1.9	–
N for knee*	8390	8190	8141	–
Model 1 (95% CI)	1.00 (reference)	1.26 (0.77, 2.05)	2.01 (1.25, 3.24)	0.003
Model 2 (95% CI)	1.00 (reference)	1.26 (0.78, 2.06)	1.94 (1.21, 3.12)	0.004
Model 3 (95% CI)	1.00 (reference)	1.24 (0.76, 2.02)	2.00 (1.24, 3.23)	0.003
Model 4 (95% CI)	1.00 (reference)	1.27 (0.78, 2.07)	2.11 (1.31, 3.38)	0.001
Model 5 (95% CI)	1.00 (reference)	1.22 (0.75, 1.99)	1.95 (1.21, 3.12)	0.004
Model 6 (95% CI)	1.00 (reference)	1.24 (0.76, 2.02)	2.00 (1.24, 3.22)	0.003

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 zinc (tertiles) on the basis of model 1 (n = 12,362);

Model 6 added serum phosphorus (tertiles) on the basis of model 1 (n = 12,264)

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

N, number; CI, confidence interval