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.

^aAt recruitment unless otherwise stated.

^bBased on place of residence ACORN score (Solutions CI, 2002).

^cLow: ‘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’.

^dAged <20 at recruitment.

^eWake and put the lights on or go into a bright room.

^fGoing to sleep at or after 0200 hours or rising for the day at or before 0100 hours (Davis et al, 2001).