Table 3.

Association of night shift work with female breast cancer in the hospital subcohort according to earlier shift work exposure (based on the first survey, n=20 763)

							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
Day work always	10	82	8759	25	354	10 653	Ref		Ref		Ref		Ref
Shift work with nights at baseline	30	232	24 393	196	3112	91 297	1.22	0.60 to 2.50	0.72	0.48 to 1.10	1.36	0.63 to 2.97	0.68	0.41 to 1.12
Day work always	10	82	8759	25	354	10 653	Ref		Ref		Ref		Ref
Shift work with nights, 5–9 years	4	30	10 587	8	124	19 056	0.37	0.12 to 1.19	0.18	0.08 to 0.40	0.69	0.20 to 2.41	0.37	0.16 to 0.88
Shift work with nights, 10–14 years	7	56	6066	19	294	15 228	1.12	0.43 to 2.95	0.44	0.24 to 0.79	1.48	0.52 to 4.15	0.60	0.31 to 1.17
Shift work with nights, 15+ years	19	146	7483	168	2685	55 167	2.45	1.14 to 5.28	0.90	0.59 to 1.37	1.65	0.72 to 3.81	0.72	0.44 to 1.19
							Trend: p=0.003†		Trend: p=0.006†		Trend: p=0.151†		P=0.926†

HR and 95% CI from Cox regression models according to earlier shift work experience.

*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.

†P value indicates a trend test for linearity in relation to earlier exposure time.

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