Table 3. Analysis of potential interactions between percent density and other risk factors, after adjustment for BMI.
|
OR (95% CI)
|
||||||||
|---|---|---|---|---|---|---|---|---|
| Risk factor | Categories | A+B (0–10%) | C (11–25%) | D (26–50%) | E (51–75%) | F (76–100%) | P-value | P-valuea |
| BMI | <26.7b | 1.00 | 1.32 (0.66–2.66) | 2.60 (1.34–5.01) | 4.13 (2.09–8.14) | 3.95 (1.53–10.17) | 0.3 | 0.02 |
| ⩾26.7 | 1.00 | 0.88 (0.44–1.74) | 2.19 (1.17–4.12) | 5.24 (2.36–11.65) | 9.53 (0.93–97.49) | |||
| Age of menarche | <14 | 1.00 | 1.32 (0.62–2.77) | 2.81 (1.40–5.62) | 4.53 (2.13–9.63) | 5.70 (1.52–21.31) | 0.6 | 0.8 |
| ⩾14 | 1.00 | 1.07 (0.56–2.03) | 2.61 (1.44–4.71) | 4.73 (2.50–8.98) | 5.90 (2.13–16.32) | |||
| Parity | Nulliparous | 1.00 | 0.56 (0.06–5.00) | 0.88 (0.11–7.16) | 1.13 (0.14–9.36) | 3.11 (0.20–47.90) | 0.2 | 0.5 |
| Parous | 1.00 | 1.15 (0.69–1.89) | 2.74 (1.72–4.37) | 4.90 (2.92–8.23) | 5.54 (2.32–13.22) | |||
| No. of deliveries | <3 | 1.00 | 0.55 (0.20–1.50) | 1.33 (0.52–3.37) | 2.23 (0.86–5.77) | 2.28 (0.59–8.70) | 0.3 | 0.8 |
| ⩾3 | 1.00 | 1.36 (0.77–2.42) | 3.10 (1.81–5.30) | 5.29 (2.90–9.63) | 8.17 (2.85–23.45) | |||
| Age at first birth | <30 | 1.00 | 1.39 (0.78–2.48) | 3.40 (1.97–5.87) | 5.86 (3.23–10.65) | 5.27 (1.97–14.07) | 0.1 | 0.7 |
| (excluding nulliparous) | ⩾30 | 1.00 | 0.33 (0.08–1.33) | 0.46 (0.12–1.68) | 1.17 (0.30–4.58) | 1.09 (0.10–11.96) | ||
| Breastfeeding | Never | 1.00 | 2.02 (0.79–5.19) | 3.45 (1.39–8.50) | 5.31 (2.05–13.70) | 3.19 (0.77–13.18) | 0.2 | 0.1 |
| Ever | 1.00 | 0.83 (0.44–1.54) | 2.27 (1.29–3.98) | 4.69 (2.49–8.82) | 6.30 (1.95–20.33) | |||
| OC use | Never | 1.00 | 1.11 (0.60–2.02) | 3.12 (1.79–5.45) | 5.60 (3.07–10.21) | 6.83 (2.51–18.55) | 0.1 | 0.02 |
| Ever | 1.00 | 1.19 (0.52–2.70) | 2.14 (0.98–4.62) | 3.30 (1.45–7.48) | 4.24 (1.09–16.51) | |||
| HRT use | Never | 1.00 | 1.10 (0.66–1.83) | 2.34 (1.44–3.78) | 4.39 (2.59–7.43) | 6.13 (2.50–15.01) | 0.8 | 0.8 |
| Ever | 1.00 | 1.68 (0.30–9.32) | 7.19 (1.47–35.19) | 8.65 (1.74–42.93) | 6.83 (0.77–60.33) | |||
| Menopausal status | Not post menopausal | 1.00 | 1.31 (0.11–14.71) | 3.12 (0.31–30.96) | 6.65 (0.66–66.33) | 3.92 (0.28–53.38) | 0.8 | 0.8 |
| Post menopausal | 1.00 | 1.14 (0.69–1.87) | 2.67 (1.68–4.26) | 4.35 (2.60–7.28) | 6.81 (2.76–16.78) | |||
| Age at screening | <55 years | 1.00 | 1.02 (0.29–3.49) | 2.94 (0.95–9.05) | 5.14 (1.61–16.39) | 7.42 (1.74–31.62) | 0.5 | 0.96 |
| ⩾55 years | 1.00 | 1.18 (0.69–2.01) | 2.60 (1.58–4.27) | 4.48 (2.56–7.82) | 4.84 (1.70–13.77) | |||
| Ethnicity | Chinese | 1.00 | 0.92 (0.53–1.57) | 2.09 (1.27–3.42) | 3.80 (2.23–6.49) | 4.75 (1.94–11.57) | 0.4 | 0.7 |
| Non-Chinese | 1.00 | 2.74 (0.81–9.15) | 7.52 (2.38–23.75) | 9.16 (2.27–36.99) | 13.89 (2.07–93.51) | |||
Abbreviations: BMI=body mass index; CI=confidence interval; HRT=hormone replacement therapy; OC=oral contraceptive; OR=odds ratio.
a
P-value obtained by taking the single degree of freedom interaction of two continuous variables (For example, BMI and percent density on continuous scale).
b
Upper quartile boundary of BMI.