Table 1.

Comparison of selected risk factors between MZ and DZ individual twin participants in the current mammographic density study and all other twins in the California Twin Study

MZ
DZ
ParticipantsOther California twinsParticipantsOther California twins
Age on 12/31/99
    <51208 (40.5%)1,126 (73.5%)284 (48.0%)1,036 (68.8%)
    51-60288 (56.0%)340 (22.2%)278 (47.0%)408 (27.1%)
    >6018 (3.5%)66 (4.3%)30 (5.1%)62 (4.1%)
    P*<0.001<0.001
BMI
    <26331 (64.5%)959 (63.5%)380 (64.6%)972 (65.5%)
    26-2973 (14.2%)264 (17.5%)89 (15.1%)221 (14.9%)
    ≥30109 (21.3%)287 (19.0%)119 (20.2%)291 (19.6%)
    P*0.180.93
Hip/waist ratio
    Hips > waist467 (91.0%)1,292 (85.5%)538 (91.5%)1,290 (87.0%)
    Hips = waist or hips < waist46 (9.0%)220 (14.6%)50 (8.5%)192 (13.0%)
    P*0.0010.005
Alcohol use monthly
    0-2 drinks251 (50.2%)848 (56.5%)282 (48.8%)826 (56.3%)
    >2 drinks249 (49.8%)654 (43.5%)296 (51.2%)641 (43.7%)
    P*0.0150.002
Age of menarche
    ≤11117 (22.8%)295 (19.5%)129 (21.8%)328 (22.1%)
    12140 (27.2%)459 (30.3%)176 (29.7%)420 (28.2%)
    13159 (30.9%)482 (31.8%)199 (33.6%)459 (30.8%)
    ≥1498 (19.1%)279 (18.4%)88 (14.9%)282 (18.9%)
    P*0.330.15
No. live births
    0132 (25.8%)410 (27.3%)116 (20.0%)395 (26.8%)
    1-2292 (57.0%)796 (53.0%)339 (57.6%)764 (51.8%)
    ≥388 (17.2%)297 (20.0%)134 (22.8%)316 (21.4%)
    P*0.240.003
Menopausal status
    Premenopausal368 (91.8%)1,280 (94.8)436 (92.8%)1,229 (94.8%)
    Postmenopausal33 (8.2%)70 (5.2)34 (7.2%)68 (5.2%)
    P*0.0230.11
  • * χ2 P value.

  • At the time of original twin questionnaire.