Body fatness during childhood and adolescence and incidence of breast cancer in premenopausal women: a prospective cohort study

Table 3 Relative risks of breast cancer by changes in body fatness between ages 5, 10, and 20 years among 109,267 premenopausal Nurses' Health Study II participants (1989–2001)

	Cases^a (n = 1318)	Person-years	Age-adjusted RR (95% CI)	Multivariate RR (95% CI)^b	Multivariate RR + starting figure^c
Change from ages 5 to 10 years
Decreased	76	59,972	0.97 (0.77–1.23)	0.94 (0.74–1.19)	1.04 (0.82–1.32)
No change	950	720,994	1.00 (ref.)	1.00 (ref.)	1.00 (ref.)
Increased 1 level	218	194,725	0.87 (0.75–1.01)	0.88 (0.76–1.02)	0.88 (0.76–1.02)
Increased 2 or more levels	74	69,001	0.79 (0.62–1.00)	0.79 (0.62–1.00)	0.77 (0.61–0.98)
Change from ages 10 to 20 years
Decreased	223	184,978	0.86 (0.74–1.01)	0.86 (0.74–1.01)	1.06 (0.89–1.27)
No change	497	353,987	1.00 (ref.)	1.00 (ref.)	1.00 (ref.)
Increased 1 level	463	388,462	0.92 (0.81–1.04)	0.92 (0.81–1.05)	0.85 (0.74–0.97)
Increased 2 or more levels	135	117,264	0.93 (0.77–1.12)	0.92 (0.76–1.11)	0.82 (0.67–0.99)
Change from ages 5 to 20 years
Decreased	172	135,479	0.91 (0.76–1.08)	0.90 (0.75–1.07)	1.06 (0.88–1.29)
No change	449	321,121	1.00 (ref.)	1.00 (ref.)	1.00 (ref.)
Increased 1 level	474	384,088	0.94 (0.83–1.08)	0.95 (0.83–1.08)	0.88 (0.77–1.01)
Increased 2 or more levels	223	204,003	0.87 (0.74–1.02)	0.86 (0.74–1.02)	0.77 (0.65–0.91)

^aIncluding both invasive and in situ cases. ^bAdjusted for age (months), time period (6 periods), birthweight (<5.5, 5.5–6.9, 7–8.4, 8.5–9.9, ≥ 10 lb), height (inches), recent alcohol consumption (0, 0.1–1.4, 1.5–4.9, 5.0–9.9, ≥ 10 g/day), parity and age at first birth (nulliparous, 1–2 pregnancies with age at first birth <25 years, 1–2 pregnancies with age at first birth 25–29 years, 1–2 pregnancies with age at first birth ≥ 30 years, ≥ 3 pregnancies with age at first birth <25 years, ≥ 3 pregnancies with age at first birth 25–29 years, ≥ 3 pregnancies with age at first birth ≥ 30 years), oral contraceptive use (never, past use <4 years, past use ≥ 4 years, current use <4 years, current use ≥ 4 years), history of benign breast disease (yes, no), and first-degree family history of breast cancer (yes, no). ^cAdjusted for same factors as above, plus figure at age 5 years (for change from ages 5 to 10 years and from ages 5 to 20 years) or at age 10 years (for change from ages 10 to 20 years), each modeled as an ordinal variable. CI, confidence interval; RR, relative risk.

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