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

Table 5

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

Estradiol (pg/mL)	β (95% CI) -value
20-55 year-old female
Fitting by the standard linear model	−127.949 (−259.289, 3.391) 0.0565
Fitting by the two-piecewise linear model
Inflection point (K)	1.39
Serum selenium <1.39 umol/L	−708.164 (−1304.787, −111.540) 0.0202
Serum selenium >1.39 umol/L	−44.255 (−199.963, 111.453) 0.5776
Equation predictions at breakpoints	116.283 (70.943, 161.624)
Log likelihood ratio	0.048

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