Table 4.

Multivariate-Adjusted Relative Risk^a of Breast Cancer According to Self-Reported Average Adolescent Body Fatness and Other Characteristics Among Participants in the Nurses’ Health Study (1988–2004) and Nurses’ Health Study II (1989–2005)

Characteristic	No. of Cases	RR by Average Adolescent Body Fatnessb (Ages 10–20 Years)								Ptrend
		1 (Referent)	1.5–2	2.5–3	3.5–4	≥4.5		Per 1-Unit Increase
						RR	95% CI	RR	95% CI
Birth weight, pounds (kg)
<8.5 (<3.9)	4,992	1.0	0.97	0.91	0.80	0.64	0.56, 0.73	0.89	0.87, 0.92	<0.0001
≥8.5 (≥3.9)	809	1.0	1.13	1.07	0.96	0.90	0.64, 1.27	0.94	0.89, 1.00	0.05
Pinteraction = 0.04
Height, inches (cm)
≤63 (≤161)	2,263	1.0	1.22	1.08	0.97	0.89	0.73, 1.09	0.93	0.89, 0.96	<0.0001
64–65 (162–166)	2,346	1.0	0.89	0.85	0.73	0.65	0.54, 0.79	0.90	0.86, 0.93	<0.0001
≥66 (≥167)	2,969	1.0	0.92	0.91	0.81	0.58	0.49, 0.69	0.89	0.87, 0.92	<0.0001
Pinteraction = 0.20
Current body mass indexc
Premenopausal women
<22	649	1.0	0.98	0.86	0.86	0.63	0.37, 1.07	0.90	0.83, 0.98	0.02
22–24.9	643	1.0	0.88	0.83	0.74	0.55	0.34, 0.87	0.88	0.82, 0.96	0.002
≥25	895	1.0	1.20	1.14	1.11	0.73	0.43, 1.22	0.88	0.83, 0.94	<0.0001
Pinteraction = 0.38
Postmenopausal women
<22	889	1.0	0.93	0.94	0.81	0.53	0.36, 0.77	0.90	0.84, 0.96	0.002
22–24.9	1,339	1.0	1.05	0.91	0.79	0.74	0.57, 0.97	0.90	0.85, 0.95	<0.0001
25–29.9	1,668	1.0	1.02	0.99	0.77	0.73	0.58, 0.91	0.91	0.87, 0.94	<0.0001
≥30	1,076	1.0	0.86	0.76	0.65	0.61	0.46, 0.80	0.88	0.83, 0.92	<0.0001
Pinteraction = 0.55
Family history of breast cancer
No family history	6,214	1.0	0.98	0.90	0.81	0.68	0.60, 0.76	0.90	0.88, 0.92	<0.0001
Family history	1,368	1.0	1.09	1.09	0.96	0.71	0.54, 0.92	0.91	0.87, 0.96	0.0003
Pinteraction = 0.29
Parity
Nulliparous	890	1.0	0.96	1.01	0.97	0.62	0.46, 0.85	0.91	0.86, 0.96	0.001
Parous	6,479	1.0	1.00	0.92	0.82	0.71	0.63, 0.80	0.91	0.89, 0.93	<0.0001
Pinteraction = 0.83
Age at menarche, years
<13	3,902	1.0	1.07	0.95	0.88	0.74	0.63, 0.86	0.90	0.88, 0.93	<0.0001
≥13	3,631	1.0	0.93	0.93	0.77	0.60	0.51, 0.71	0.90	0.87, 0.92	<0.0001
Pinteraction = 0.50
Menstrual cycle pattern at ages 18–22 years
Regular	5,775	1.0	1.01	0.94	0.84	0.70	0.62, 0.79	0.91	0.89, 0.93	<0.0001
Irregular	1,704	1.0	0.94	0.91	0.79	0.62	0.50, 0.77	0.89	0.85, 0.93	<0.0001
Pinteraction = 0.41
Postmenopausal hormone use (postmenopausal women only)
Never use	1,247	1.0	0.95	0.89	0.86	0.89	0.71, 1.12	0.97	0.92, 1.01	0.15
Past use	960	1.0	0.98	1.05	0.75	0.67	0.50, 0.89	0.89	0.84, 0.95	<0.0001
Current use	2,454	1.0	1.06	0.95	0.86	0.71	0.59, 0.86	0.90	0.87, 0.93	<0.0001
Pinteraction = 0.05

Abbreviations: CI, confidence interval; RR, relative risk.

^aMultivariate RRs were adjusted for age, time period, parity/age at first birth, family history of breast cancer, personal history of benign breast disease, height, alcohol intake, oral contraceptive use, birth weight, menopausal status, age at menopause, and postmenopausal hormone use; models stratifying on an individual factor included all variables except that factor.

^bParticipants were asked to recall their body fatness at ages 5, 10, and 20 years using a 9-level figure drawing, where level 1 represents the most lean and level 9 represents the most overweight (Figure 1) (26).

^cWeight (kg)/height (m)².