Table 3.

Risk factors associated with increased or decreased risk of breast cancer.

Factors associated with increased breast cancer risk:	women in the control group (n = 2167) (%)	patients with breast cancer (n = 1492) (%)	OR (95%CI)	P value
Age (≥ 50) years	34.0	58.8	2.78 (2.42–3.18)	< 0.001
Induced abortion	42.9	49.7	1.31 (1.13–1.53)	< 0.001
Body mass index ≥ 25	55.2	64.2	1.46 (1.27–1.68)	< 0.001
Family history of breast cancer (first degree relative)	5.0	7.2	1.46 (1.11–1.92)	0.008
Age at first birth (≥ 35 years)	0.9	2.6	3.06 (1.62–5.77)	< 0.001
Factors associated with decreased breast cancer risk:
Education (≥ 13 years)	48.8	40.3	0.71 (0.62–0.81)	< 0.001
Spontaneous abortion	28.9	22.5	0.71 (0.60–0.85)	< 0.001
Smoking	29.9	23.5	0.72 (0.61–0.85)	< 0.001
Breast feeding	98.4	91.5	0.17 (0.11–0.27)	< 0.001
Oral contraceptive use	27.8	18.4	0.59 (0.50–0.69)	< 0.001
Nullipara	20.8	16.2	0.95 (0.92–0.98)	< 0.001
Hormone replacement therapy	10.8	4.1	0.35 (0.26–0.47)	< 0.001