Table 1 Characteristics of Generations Study participants included in the analysisa

From: Domestic light at night and breast cancer risk: a prospective analysis of 105 000 UK women in the Generations Study

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 recruitment b
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 night c
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 light e
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 sleep f
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)
  1. Abbreviations: SD=standard deviation.
  2. aAt recruitment unless otherwise stated.
  3. bBased on place of residence ACORN score (Solutions CI, 2002).
  4. 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’.
  5. dAged <20 at recruitment.
  6. eWake and put the lights on or go into a bright room.
  7. fGoing to sleep at or after 0200 hours or rising for the day at or before 0100 hours (Davis et al, 2001).