Table 1

Characteristics of the study population

	Full cohort		Never worked at nights*		Ever worked at nights*
	N	%	N	%	N	%
All	25 585	100.0	15 675	61.3	9 910	38.7
Age†
<40	7 629	29.8	3 881	24.8	3 748	37.8
40–49	6 358	24.9	3 705	23.6	2 653	26.8
50+	11 598	45.3	8 089	51.6	3 509	35.4
Country of birth
Sweden	20 334	79.5	12 606	80.4	7 728	78.0
Nordic countries except Sweden	1 546	6.0	971	6.2	575	5.8
Europe except Nordic countries	1 228	4.8	685	4.4	543	5.5
Outside Europe	2 475	9.7	1 413	9.0	1 062	10.7
Profession
Nurses including midwives	14 977	58.5	8 821	56.3	6 156	62.1
Nursing assistants, others	10 608	41.5	6 854	43.7	3 754	37.9
Childbirth, yes*	19 148	74.8	12 025	76.7	7 123	71.9

*At end of follow-up.
†At beginning of follow-up.