Table 1. Characteristics of Generations Study participants included in the analysisa.
Characteristic | No. | (%) |
---|---|---|
Year of birth | ||
1908–1949 | 29 228 | (27.6) |
1950–1959 | 25 516 | (24.1) |
1960–1969 | 24 054 | (22.7) |
1970–1996 | 27 068 | (25.6) |
Age at recruitment (years) | ||
<20 | 1178 | (1.1) |
20–39 | 33 482 | (31.6) |
40–49 | 24 340 | (23.0) |
50–59 | 26 922 | (25.4) |
≥60 | 19 944 | (18.8) |
Ethnicity | ||
White | 104 595 | (98.8) |
Other or not stated | 1271 | (1.2) |
Socioeconomic status at recruitmentb | ||
1 (highest) | 46 168 | (43.6) |
2 | 10 224 | (9.7) |
3 | 31 732 | (30.0) |
4 | 11 749 | (11.1) |
5 (lowest) | 4778 | (4.5) |
Not classifiable | 1215 | (1.2) |
Menopausal status at recruitment | ||
Post-menopausal | 41 181 | (38.9) |
Pre-menopausal | 59 499 | (56.2) |
Never had periods | 34 | (0.0) |
Not known | 5152 | (4.9) |
Light at nightc | ||
At recruitment | ||
Low | 22 155 | (20.9) |
Med | 51 889 | (49.0) |
High | 31 822 | (30.1) |
At age 20 years | ||
Low | 18 750 | (17.7) |
Med | 50 116 | (47.3) |
High | 34 106 | (32.0) |
Not applicabled | 1178 | (1.1) |
Not known | 1716 | (1.6) |
History of night shift work during preceding 10 years | ||
No | 87 935 | (83.1) |
Yes | 17 931 | (16.9) |
Waking at night and exposed to lighte | ||
At recruitment | ||
No | 58 818 | (55.6) |
Yes | 38 710 | (36.6) |
Not known | 8338 | (7.9) |
At age 20 years | ||
No | 82 936 | (78.3) |
Yes | 10 183 | (9.6) |
Not applicabled | 1178 | (1.1) |
Not known | 11 569 | (10.9) |
Non-peak sleepf | ||
No | 105 116 | (99.3) |
Yes | 750 | (0.7) |
Sleep duration per night (hours) | ||
<7 | 19 288 | (18.2) |
⩾7 | 85 807 | (81.1) |
Not known | 771 | (0.7) |
Total participants | 105 866 | (100.0) |
Abbreviations: SD=standard deviation.
At recruitment unless otherwise stated.
Based on place of residence ACORN score (Solutions CI, 2002).
Low: ‘Too dark to see your hand, or you wear a mask’ Med: ‘Light enough to see your hand in front of you, but not see across the room’ High: ‘Light enough to see across the room, but not read’+‘Light enough to read’.
Aged <20 at recruitment.
Wake and put the lights on or go into a bright room.
Going to sleep at or after 0200 hours or rising for the day at or before 0100 hours (Davis et al, 2001).