Table 3.

Multivariable analyses for associations of risk factors with invasive BC among women age ≥45 years, by ER status.^*

	All invasive (n=1,534)					ER- (n=385)				ER+ (n=804)
	person-years	cases	HR	95% CI		cases	HR	95% CI		cases	HR	95% CI
Age at menarche (yrs)
≤11	124,056	442	1.00	reference		122	1.00	reference		227	1.00	reference
12–13	238,248	818	0.94	0.84	1.06	192	0.80	0.63	1.00	444	1.00	0.85	1.18
≥14	94,487	270	0.77	0.66	0.90	71	0.72	0.53	0.97	131	0.73	0.59	0.91
Oral contraceptive use
Never	113,214	397	1.00	reference		72	1.00	reference		220	1.00	reference
Ever, ≥10 yrs ago	304,717	1008	1.07	0.95	1.22	281	1.54	1.17	2.03	518	0.99	0.84	1.17
Ever, 5–10 yrs ago	17,513	56	1.34	1.00	1.80	16	1.95	1.10	3.46	25	1.08	0.70	1.66
Ever, within 5 yrs	23,408	73	1.37	1.05	1.80	16	1.51	0.85	2.69	41	1.38	0.96	1.98
Family history of breast cancer
No	411,591	1292	1.00	reference		331	1.00	reference		677	1.00	reference
Yes	47,269	242	1.57	1.36	1.80	54	1.39	1.04	1.86	127	1.55	1.28	1.88
Parity
Nulliparous	85,033	275	1.02	0.84	1.24	51	0.71	0.48	1.07	156	1.17	0.90	1.52
1 birth	105,685	377	1.00	reference		91	1.00	reference		198	1.00	reference
2 births	134,026	449	0.93	0.81	1.07	131	1.09	0.83	1.43	228	0.90	0.74	1.09
3+ births	132,098	432	0.84	0.71	0.98	112	0.92	0.68	1.26	221	0.80	0.64	0.99
Age at first birth (yrs)a
<20	125,426	397	1.00	reference		112	1.00	reference		200	1.00	reference
20–24	128,929	430	1.00	0.87	1.15	120	1.01	0.77	1.31	215	0.98	0.80	1.19
≥25	111,747	412	1.14	0.98	1.33	99	0.97	0.72	1.32	221	1.20	0.97	1.49
Years since last birtha
≥10 yrs	350,948	1198	1.00	reference		325	--	--		617	1.00	reference
<10 yrs	10,107	26	1.09	0.73	1.65	2	--	--	--	14	1.18	0.67	2.08
Lactationa
Never	220,478	746	1.00	reference		202	1.00	reference		373	1.00	reference
Ever	145,885	497	1.04	0.93	1.18	128	1.01	0.80	1.27	266	1.12	0.95	1.32
BMI at age 18 (kg/m2)
<20	202,790	727	1.00	reference		191	1.00	reference		382	1.00	reference
20–24	196,533	640	0.90	0.81	1.01	159	0.87	0.70	1.09	331	0.88	0.76	1.03
≥25	50,353	135	0.76	0.63	0.93	31	0.73	0.49	1.09	75	0.80	0.61	1.04
Current BMI (kg/m2)
<25	96,942	337	1.00	reference		84	1.00	reference		169	1.00	reference
25–29.9	158,660	527	0.95	0.82	1.09	148	1.04	0.79	1.37	279	1.00	0.82	1.21
≥30	198,604	659	1.00	0.87	1.16	151	0.87	0.65	1.17	352	1.08	0.88	1.32
Waist:hip ratio
Tertile 1 (<0.76)	105,204	324	1.00	reference		81	1.00	reference		167	1.00	reference
Tertile 2 (0.76 – 0.84)	116,588	383	1.05	0.91	1.22	106	1.17	0.87	1.57	209	1.11	0.90	1.36
Tertile 3 (>0.84)	115,305	380	1.07	0.92	1.25	98	1.11	0.82	1.51	195	1.04	0.84	1.29
Alcohol consumption (drinks)
<1/wk	317,121	1079	1.00	reference		274	1.00	reference		565	1.00	reference
1–6/wk	118,361	376	0.94	0.83	1.06	90	0.90	0.71	1.15	203	0.96	0.82	1.13
≥7/wk	22,950	79	1.01	0.80	1.27	21	1.07	0.68	1.68	36	0.88	0.63	1.24
Vigorous exercise
None	243,272	858	1.00	reference		223	1.00	reference		450	1.00	reference
<5 hrs/week	178,581	562	0.94	0.84	1.04	134	0.83	0.67	1.04	297	0.95	0.82	1.10
≥5 hrs/week	33,355	103	0.94	0.76	1.16	26	0.88	0.58	1.33	51	0.92	0.68	1.23

^*Multivariable hazards ratios (HRs) adjusted for age, smoking history (never active or passive, passive only, never active/unknown passive, 1-<10 packyears, 10+ packyears), menopausal status (premenopausal, hysterectomy only, postmenopausal age <40, postmenopausal age 40–44, postmenopausal age 45, postmenopausal age unknown or missing), postmenopausal hormone use (never, E+P <5 years duration, E+P 5+ years duration, other type), and all factors in Table 3.

^aAmong parous women only. Estimates for age at first birth adjusted for age, smoking history, menopausal status, and all factors in Table 3 except years since last birth; estimates for years since last birth adjusted for age, smoking history, menopausal status, and all factors in Table 3 except age at first birth; estimates for lactation adjusted for age, smoking history, menopausal status, and all factors in Table 3.