Table 2.

Association of shift work with female breast cancer during follow-up: survey cohort (N=33 359). Shift work status based on first two surveys with 4 years between.

							Unadjusted				Adjusted*
	Follow-up <10 years			Follow-up ≥10 years			Follow-up <10 years		Follow-up ≥10 years		Follow-up <10 years		Follow-up ≥10 years
	Cases	Pyrs		Cases	Pyrs		HR	95% CI	HR	95% CI	HR	95% CI	HR	95% CI
		Cases	All		Cases	All
All
Day work	673	3356	60 939	123	1366	164 593	Ref		Ref		Ref		Ref
Shift work without nights	138	672	9442	33	371	35 819	1.15	0.96 to 1.39	1.22	0.83 to 1.79	1.14	0.94 to 1.39	1.35	0.90 to 2.02
Shift work with nights	128	585	12 318	34	378	43 786	0.90	0.74 to 1.09	0.99	0.67 to 1.45	1.19	0.97 to 1.46	1.22	0.80 to 1.85
<50 years
Day work	362	1798	45 540	83	926	110 373	Ref		Ref		Ref		Ref
Shift work without nights	58	301	6314	16	181	21 745	1.01	0.77 to 1.34	0.97	0.57 to 1.65	1.11	0.83 to 1.49	0.99	0.57 to 1.70
Shift work with nights	81	372	10 469	19	209	33 800	0.96	0.75 to 1.22	0.72	0.44 to 1.19	1.26	0.97 to 1.64	0.91	0.53 to 1.56
50+ years
Day work	311	1558	15 398	40	440	54 219	Ref		Ref		Ref		Ref
Shift work without nights	80	371	3128	17	191	14 075	1.14	0.89 to 1.45	1.62	0.92 to 2.86	1.18	0.90 to 1.53	2.01	1.12 to 3.60
Shift work with nights	47	213	1849	15	170	9986	1.11	0.81 to 1.51	1.91	1.04 to 3.47	1.17	0.84 to 1.63	2.05	1.04 to 4.01

HR and 95% CI from Cox regression models.

*Adjusted for age, SES (1–4), children 0–6 years (no/yes/missing), children 7–18 years (no/yes/missing), smoking (yes/no/missing), alc alc*alc and bmi bmi*bmi.

Pyrs, person-years; Ref, reference; SES, socioeconomic status.