Table 1. The baseline characters for the participants in the study.

Characteristics	Controls (N = 580)	Cases (N = 593)	P-value
Age (year, ±SD)	55.3±9.3	53.0±11.3	0.001
Age at menarche (year, ±SD)	15.6±1.8	15.1±1.7	<0.001
Age at first birth (year, ±SD)	26.3±4.3	26.2±3.6	0.425
Menopausal status			<0.001
pre−/peri-menopausal	150 (26.3%)	216 (38.4%)
post-menopausal	421 (73.7%)	347 (61.6%)
Contraceptive users			0.045
yes	32 (5.5%)	49 (8.7%)
no	548 (94.5%)	512 (91.3%)
First-degree relatives’ history of breast cancer			0.693
yes	24 (4.1%)	27 (4.8%)
no	556 (95.9%)	536 (95.2%)
Season of blood collection			0.007
spring	204 (35.2%)	198 (33.4%)
summer	220 (37.9%)	183 (30.9%)
autumn	56 (9.7%)	81 (13.7%)
winter	100 (17.2%)	131 (22.1%)