Association between Serum Copper, Selenium, Zinc, and Serum Estradiol in Women

Table 3

Threshold effect analysis of serum copper and serum E2 in women using a two-piecewise linear regression model.

Estradiol (pg/mL)	β (95% CI) -value
Model 1
A straight-line effect	8.428 (6.100, 10.756) <0.0001
Model 2
Inflection point (K)	28.57
Serum copper <28.57 umol/L	−4.512 (−7.456, −1.567) 0.0027
Serum copper >28.57 umol/L	52.819 (45.911, 59.727) <0.0001
Equation predictions at breakpoints	28.139 (0.194, 56.085)
Log likelihood ratio	<0.001

Age, race, education, ratio of family income to poverty, testosterone, total, body mass index, and marital status were adjusted.