Table 4 Night shift work characteristics of 59,947 Nightingale Study participants

 Ever/never^a

 Never

11,799 (20%)

 Ever

48,050 (80%)

Total number of years worked on night shifts ^b

 1–4 years

5,695 (19%)

 5–9 years

9,349 (31%)

 10–14 years

6,103 (20%)

 15–19 years

3,612 (12%)

 20–24 years

2,668 (9%)

 25–29 years

1,676 (6%)

 ≥30 years

1,395 (5%)

Cumulative lifetime number of nights worked ^b

 <250 nights

6,082 (23%)

 250–499 nights

6,026 (23%)

 500–749 nights

4,567 (17%)

 750–999 nights

2,977 (11%)

 ≥1000 nights

7,093 (27%)

 Number of nights worked per month at cohort entry ^c

 1 night per month

653 (7%)

 2 nights per month

1,351 (14%)

 3 nights per month

1,945 (21%)

 4 nights per month

2,275 (24%)

 5–7 nights per month

1,993 (20%)

 >7 nights per month

1,223 (12%)

Number of consecutive nights worked at cohort entry ^c

 1 night in a row

625 (7%)

 2 nights in a row

2,307 (25%)

 3 nights in a row

3,092 (33%)

 4 nights in a row

2,209 (24%)

 5 nights in a row

637 (7%)

 6 nights in a row

209 (2%)

 7 nights in a row

262 (3%)

 >7 nights in a row

20 (<1%)

 Type and direction of shift system at cohort entry ^c

 Permanent

690 (7%)

 Forward rotating

1,323 (14%)

 Backward rotating

27 (<1%)

 Variable

7,287 (77%)

 Don’t know/missing

85 (1%)