Table 1.
Distributions of demographic and reproductive factors and associations with the risk of breast cancer, Seoul Breast Cancer Study.
| Demographic and Reproductive Factors | Cases N = 1970 | Controls N = 2052 | OR c | 95% CI | ||
|---|---|---|---|---|---|---|
| Mean ± SD | % | Mean ± SD | % | |||
| Age | 49.0 ± 8.26 | 51.4 ± 7.75 | 0.99 | 0.98–1.01 | ||
| Family history. yes | 4.8 | 1.8 | 2.64 | 1.77–3.94 | ||
| Height | 157.9 ± 5.04 | 155.9 ± 5.00 | 1.07 | 1.06–1.08 | ||
| <160 cm | 59.6 | 75.7 | 1.00 | reference | ||
| ≥160 cm | 40.4 | 24.3 | 1.92 | 1.67–2.20 | ||
| BMI (kg/m2) | 23.2 ± 2.94 | 23.7 ± 2.96 | 0.97 | 0.95–1.00 | ||
| <25 | 76.8 | 71.2 | 1.00 | reference | ||
| ≥25 | 23.2 | 28.9 | 0.81 | 0.69–0.93 | ||
| Menarche age | 14.8 ± 1.65 | 15.2 ± 1.77 | 0.90 | 0.86–0.93 | ||
| ≥14 years | 78.9 | 85.0 | 1.00 | reference | ||
| <14 years | 21.1 | 15.0 | 1.27 | 1.07–1.50 | ||
| Ever pregnancy | 93.5 | 92.8 | 0.26 | 0.14–0.46 | ||
| Age at FFTP a | 25.9 ±3.48 | 25.1 ± 3.36 | 1.05 | 1.03–1.07 | ||
| <27 years | 55.6 | 66.4 | 1.00 | reference | ||
| Nulliparity or ≥27 years | 44.4 | 33.6 | 1.49 | 1.30–1.70 | ||
| No. of children | 2.2 ± 0.85 | 2.3 ± 0.91 | 1.06 | 0.97–1.16 | ||
| ≥2 | 85.2 | 88.2 | 1.00 | reference | ||
| <2 | 14.8 | 11.8 | 1.11 | 0.91–1.36 | ||
| Never breastfeeding | 22.3 | 14.5 | 1.31 d | 1.10–1.57 | ||
| Breastfeeding duration (months) | 18.0 ± 22.59 | 24.0 ± 21.53 | 0.99 d | 0.99–1.00 | ||
| Breastfeeding duration per child (months) | 7.3 ± 8.01 | 9.9 ± 7.27 | 0.97 d | 0.96–0.98 | ||
| ≥2.5 month | 45.1 | 68.3 | 1.00 | reference | ||
| <2.5 month | 54.9 | 31.7 | 3.81 d | 3.16–4.59 | ||
| Duration of EEBF b | 12.5 ± 6.78 | 11.7 ± 8.00 | 1.04 e | 1.02–1.05 | ||
| <13 years | 61.1 | 76.2 | 1.00 | reference | ||
| ≥13 years | 38.9 | 23.8 | 1.75 e | 1.51–2.03 | ||
| Postmenopausal women | 38.2 | 54.8 | 0.60 | 0.50–0.72 | ||
| Age at menopause | 48.5 ± 5.40 | 49.2 ± 4.55 | 0.96 | 0.94–0.98 | ||
a FFTP first full-term pregnancy (years); b EEBF estrogen exposure before the first full-term pregnancy (years); c ORs analyzed by logistic regression adjusting for age, family history, categorical FFTP, age at menarche, and menopausal status; d ORs analyzed by logistic regression adjusting for age, family history, categorical FFTP, age at menarche, menopausal status, and the number of children; e ORs analyzed by logistic regression adjusting for age, family history, ever pregnancy, and menopausal status.