Table 2.

Association between anthropometric variables and other characteristics of the study population and mammographic density (Boyd’s semiquantitative classification)

		Mammographic density
Variable	N	<10 % (A + B) (%)	>50 % (E + F) (%)	ORab	95 % CIab	P valueab
Anthropometric variables
BMI (kg/m2)
<23.9	712	9	43	1.00
23.9–26.3	711	15	31	0.71	0.58–0.86	<0.001
26.3–28.5	711	22	21	0.52	0.42–0.64	<0.001
28.5–31.7	711	32	13	0.35	0.28–0.43	<0.001
>31.7	711	46	6	0.22	0.17–0.28	<0.001
Per 1				0.88	0.87–0.89	<0.001
Waist (cm)
<77.8	711	8	44	1.00
77.8–84.0	749	16	30	0.85	0.68–1.06	0.142
54.1–90.0	667	21	19	0.65	0.51–0.83	0.001
90.1–97.1	710	33	12	0.52	0.39–0.70	<0.001
>97.1	709	46	8	0.49	0.35–0.68	<0.001
Per 10				0.66	0.59–0.74	<0.001
Hip (cm)
< 97	719	12	40	1.00
97.1–101.6	700	17	27	0.94	0.76–1.16	0.575
101.7–105.9	711	22	23	1.02	0.81–1.28	0.888
106.0–112.0	731	28	15	1.00	0.77–1.30	0.980
> 112.0	682	45	9	1.07	0.77–1.47	0.691
Per 10				1.00	0.93–1.07	0.948
Waist-to-hip ratio
< 0.78	709	9	40	1.00
0.78–0.82	709	20	27	0.79	0.65–0.96	0.018
0.82–0.85	707	22	22	0.73	0.60–0.89	0.002
0.85–0.89	709	33	13	0.53	0.43–0.65	<0.001
>0.89	709	38	11	0.54	0.43–0.67	<0.001
Per 0.1 increase				0.69	0.62–0.77	<0.001
Waist-to-height ratio
< 0.49	711	7	47	1.00
0.49–0.53	707	14	30	0.72	0.57–0.90	0.004
0.53–0.57	708	23	18	0.52	0.40–0.67	<0.001
0.57–0.62	710	30	13	0.44	0.33–0.59	<0.001
> 0.62	710	48	7	0.34	0.24–0.48	<0.001
Per 0.1 increase				0.49	0.41–0.59	<0.001
Weight at age 18 (kg)
< 48	675	21	28	1.00
48–50	759	19	29	1.04	0.86–1.26	0.693
51–54	451	22	22	0.82	0.66–1.02	0.069
55–59	578	23	21	0.84	0.69–1.04	0.108
> 59	544	36	13	0.58	0.47–0.72	0.000
Unknown	549	29	20	0.89	0.72–1.10	0.263
Per 5 kg increase				0.89	0.85–0.93	<0.001
Adult weight gain (kg)
<6	576	15	34	1.00
6–12	631	15	29	1.24	1.01–1.52	0.044
12–18	664	22	24	1.34	1.08–1.66	0.007
18–24	500	29	20	1.44	1.13–1.83	0.003
>24	636	38	11	1.86	1.40–2.44	0.000
Unknown	549	29	20	1.43	1.13–1.80	0.003
Per 6 kg of gain				1.18	1.11–1.24	<0.001
Other variables
Age (years)
<50	548	10	42	1.00
50–54	973	20	28	0.75	0.61–0.92	0.006
55–59	1,001	25	18	0.6	0.51–0.79	<0.001
60–64	939	37	12	0.50	0.39–0.65	<0.001
≥65	95	38	15	0.52	0.33–0.82	0.004
Per 5 years				0.85	0.78–0.93	<0.001
Time since menopause (years)
0	819	13	41	1.00
<5	739	21	23	0.68	0.560.83	<0.001
5–10	863	27	17	0.57	0.46–0.71	<0.001
10–15	659	33	15	0.53	0.41–0.69	<0.001
>15	476	35	13	0.49	0.36–0.66	<0.001
Per 5 years				0.89	0.83–0.95	<0.001
Parity
Nuliparous	319	15	35	1.00
1	542	18	33	0.76	0.59–0.98	0.038
2	1,708	24	22	0.56	0.445–0.71	<0.001
3	716	29	18	0.53	0.41–0.67	<0.001
4	188	36	6	0.37	0.26–0.51	<0.001
5 or more	83	41	4	0.26	0.14–0.41	<0.001
Per birth				0.80	0.75–0.84	<0.001
Family history of breast cancer
No	3,297	25	22	1.00
Yes	260	21	29	1.29	1.02–1.63	0.033
Hormonal Replacement Therapy
No	3,200	24	23	1.00
Current use	88	23	24	0.75	0.50–1.11	0.145
Past use	270	31	18	0.86	0.68–1.08	0.189
Bra size
80–85	418	9	43	1.49	1.20–1.85	<0.001
90	654	16	30	1.04	0.87–1.24	0.695
95	1,011	22	25	1.00
100	656	28	15	0.90	0.75–1.08	0.262
105	424	35	13	0.85	0.69–1.06	0.151
110	242	41	8	0.87	0.66–1.14	0.310
115–120	134	56	4	0.62	0.43–0.89	0.009
Unknown	17	29	24	0.83	0.34–2.02	0.679
Bra size per 5 cm				0.90	0.86–0.94	<0.001

^aORs and 95 % confidence interval (95 % CI) adjusted for age, BMI, bra size, time since menopause, parity, family history of breast cancer and hormonal replacement treatment use

^bIn italics ORs 95 %CI and P values obtained with the corresponding variable as a continuous term