Table 1.
Characteristics of study participants (N = 257), Madison, Wisconsin, 2008–2009
| N | Percent | Age-adjusted mean% densitya (95% CI) | Multivariable-adjustedb mean% densitya (95% CI) | |
|---|---|---|---|---|
| Age | ||||
| 55–59 | 133 | 51.8 | 15.3 (13.3, 17.4)c | 14.8 (13.2, 16.6) |
| 60–64 | 71 | 27.6 | 11.1 (8.9, 13.6)c | 11.7 (9.7, 13.9) |
| 65–70 | 53 | 20.6 | 11.3 (8.7, 14.2)c | 11.5 (9.3, 14.1) |
| Ptrend = 0.01 | Ptrend = 0.01 | |||
| Body mass index (kg/m2) | ||||
| <18.5 | 2 | 0.8 | 31.0 (13.6, 15.5) | 28.9 (12.5, 51.9) |
| 18.5–24.9 | 78 | 30.4 | 21.4 (18.7, 24.3) | 20.7 (18.1, 23.5) |
| 25.0–29.9 | 81 | 31.5 | 12.0 (10.0, 14.1) | 12.4 (10.5, 14.5) |
| ≥30.0 | 94 | 36.6 | 8.7 (7.2, 10.4) | 8.8 (7.3, 10.5) |
| Missing | 2 | 0.8 | – | – |
| Ptrend < 0.0001 | Ptrend < 0.0001 | |||
| Age at menarche | ||||
| ≤11 | 61 | 23.7 | 10.9 (8.6, 13.6) | 12.4 (10.1, 14.8) |
| 12–13 | 149 | 58.0 | 12.8 (11.2, 14.6) | 13.0 (11.5, 14.5) |
| 14+ | 47 | 18.3 | 18.1 (14.7, 22.0) | 15.4 (12.6, 18.5) |
| Ptrend = 0.002 | Ptrend = 0.13 | |||
| Parity | ||||
| 0 | 65 | 25.3 | 15.5 (12.7, 18.6) | 14.7 (12.4, 17.3) |
| 1 | 33 | 12.8 | 13.5 (9.9, 17.6) | 15.4 (12.1, 19.2) |
| 2 | 92 | 35.8 | 12.5 (10.4, 14.8) | 12.3 (10.5, 14.3) |
| 3+ | 67 | 26.1 | 12.0 (9.6, 14.7) | 12.1 (10.1, 14.4) |
| Ptrend = 0.06 | Ptrend = 0.05 | |||
| Age at first birthd | ||||
| <24 | 73 | 38.0 | 10.5 (8.4, 12.9) | 11.8 (9.8, 14.0) |
| 24–29 | 69 | 35.9 | 14.5 (11.9, 17.4) | 13.4 (11.2, 15.7) |
| 30 | 50 | 26.0 | 12.6 (9.8, 15.7) | 12.0 (9.5, 14.8) |
| Ptrend = 0.20 | Ptrend = 0.82 | |||
| Age at menopause | ||||
| <50 | 67 | 26.1 | 13.0 (10.5, 15.8) | 13.5 (11.3, 15.9) |
| 50–54 | 137 | 53.3 | 13.4 (11.6, 15.4) | 13.3 (11.8, 15.0) |
| 55+ | 48 | 18.7 | 13.3 (10.3, 16.6) | 12.7 (10.2, 15.6) |
| Missing | 5 | 2.0 | – | – |
| Ptrend = 0.86 | Ptrend = 0.70 | |||
| Breastfeeding durationd | ||||
| Never | 52 | 2.1 | 10.5 (8.0, 13.3) | 11.9 (9.6, 14.4) |
| ≤1 year | 79 | 27.1 | 12.0 (9.8, 14.4) | 11.7 (9.8, 13.7) |
| >1 year | 57 | 41.2 | 15.1 (12.1, 18.3) | 14.0 (11.6, 16.7) |
| Missing | 4 | 29.7 | – | – |
| Ptrend = 0.03 | Ptrend = 0.25 | |||
| Oral contraceptive use | ||||
| Never | 52 | 20.2 | 13.9 (10.9, 17.2) | 13.6 (11.0, 16.5) |
| <10 years | 149 | 58.0 | 12.7 (11.0, 14.5) | 13.2 (11.7, 14.7) |
| ≥10 years | 55 | 21.4 | 14.0 (11.2, 17.2) | 13.1 (10.7, 15.7) |
| Missing | 1 | 0.4 | – | – |
| Ptrend = 0.92 | Ptrend = 0.79 | |||
| Alcohol consumption (drinks/week) | ||||
| None | 93 | 36.2 | 13.0 (10.8, 15.3) | 13.3 (11.4, 15.3) |
| <5 per week | 122 | 47.5 | 13.6 (11.7, 15.7) | 13.2 (11.6, 15.0) |
| ≥5 per week | 31 | 12.1 | 13.1 (9.4, 17.3) | 13.2 (10.0, 16.8) |
| Missing | 11 | 4.3 | – | – |
| Ptrend = 0.83 | Ptrend = 0.95 | |||
| Vigorous physical activity (h/week) | ||||
| 0–1.0 | 76 | 29.6 | 11.5 (9.3, 13.9) | 12.4 (10.4, 14.5) |
| 1.1–4.0 | 90 | 35.0 | 12.3 (10.3, 14.6) | 12.3 (10.4, 14.2) |
| >4.0 | 91 | 35.4 | 15.8 (13.4, 18.3) | 15.1 (13.0, 17.2) |
| Ptrend = 0.01 | Ptrend = 0.07 | |||
| Pack years of smoking | ||||
| None | 156 | 60.7 | 15.0 (13.2, 16.8) | 14.3 (12.8, 15.9) |
| 1–15 | 47 | 18.3 | 11.7 (8.9, 14.8) | 12.8 (10.2, 15.6) |
| >15 | 44 | 17.1 | 9.6 (7.0, 12.5) | 10.3 (8.0, 13.0) |
| Missing | 10 | 3.9 | – | – |
| Ptrend = 0.002 | Ptrend = 0.01 | |||
| First degree family history of breast cancer | ||||
| No | 197 | 76.7 | 14.1 (12.6, 15.8) | 13.9 (12.6, 15.3) |
| Yes | 60 | 23.4 | 10.6 (8.2, 13.2) | 11.1 (9.0, 13.4) |
| Ptrend = 0.02 | Ptrend = 0.04 | |||
| Education | ||||
| High school | 46 | 17.9 | 10.1 (7.5, 13.1) | 12.4 (9.8, 15.4) |
| Some college | 58 | 22.6 | 11.6 (9.1, 14.4) | 13.4 (11.0, 16.1) |
| College diploma | 75 | 29.2 | 15.2 (12.6, 17.9) | 14.3 (12.1, 16.6) |
| Advanced degree | 77 | 30.0 | 14.4 (12.0, 17.1) | 12.6 (10.5, 14.9) |
| Missing | 1 | 0.4 | – | – |
| Ptrend = 0.01 | Ptrend = 0.93 | |||
CI, confidence interval
aMean percent density displayed is reverse transformed from model of square root density
bAdjusted for age (continuous), body mass index (continuous), parity (0, 1,2, 3+), vigorous physical activity (0–1.0, 1.1–4.0, >4.0 h/week), pack years of smoking (None, 1–15, >15), and family history of breast cancer (No, Yes)
cMean density values by age group are not age-adjusted
dAmong parous women only