Table 1.
Characteristics of participants at Whitehall II phase 9 (2007–2009).
| N = 3064 | Chronic insomnia symptomsa |
Recurrent short sleep durationb |
|||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean (SD) or (%) | All (N = 3064) | No occurrences (N = 1998) | One occurrence (N = 524) | Two occurrences (N = 310) | Three occurrences (N = 232) | P value | No occurrences (N = 2672) | One occurrence (N = 234) | Two occurrences (N = 90) | Three occurrences (N = 68) | P value |
| Mean Cortisol at: | |||||||||||
| Waking (nmol/l) | 14.8 (7.3) | 15.1 (7.4) | 14.5 (6.8) | 14.6 (6.9) | 14.0 (7.6) | 0.05c | 15.0 (7.3) | 14.2 (7.1) | 13.2 (7.8) | 12.4 (7.6) | <0.001c |
| Waking + 30 min (nmol/l) | 21.3 (10.6) | 21.3 (10.7) | 21.4 (10.2) | 21.3 (10.7) | 21.5 (10.1) | 0.91c | 21.4 (10.5) | 20.9 (10.8) | 22.2 (11.1) | 20.1 (10.1) | 0.60c |
| Waking + 2.5 h (nmol/l) | 9.7 (6.0) | 9.6 (5.9) | 9.8 (5.7) | 9.6 (6.1) | 9.9 (6.4) | 0.89c | 9.6 (5.9) | 10.0 (5.9) | 10.3 (6.6) | 10.6 (7.3) | 0.38c |
| Waking + 8 h (nmol/l) | 6.0 (3.6) | 5.8 (3.3) | 5.8 (3.5) | 5.8 (3.5) | 6.0 (4.0) | 0.84c | 5.9 (3.5) | 6.2 (4.0) | 5.8 (3.8) | 5.9 (3.6) | 0.77c |
| Waking + 12 (nmol/l) | 3.4 (2.8) | 3.4 (2.8) | 3.4 (2.8) | 3.2 (2.5) | 3.3 (2.2) | 0.71c | 3.3 (2.7) | 3.8 (3.2) | 3.5 (2.2) | 2.9 (2.0) | 0.03c |
| Bedtime (nmol/l) | 2.5 (2.4) | 2.6 (2.4) | 2.6 (2.5) | 2.5 (2.6) | 2.3 (1.8) | 0.59c | 2.5 (2.2) | 3.1 (3.6) | 2.9 (3.2) | 3.4 (3.4) | 0.004c |
| Waking time | 06:58 | 07:00 | 06:55 | 06:51 | 06:57 | 0.07d | 07:01 | 06:45 | 06:41 | 06:27 | <0.001d |
| High stress | 2.45 | 1.70 | 2.9 | 3.2 | 6.9 | <0.001e | 2.2 | 3.0 | 3.3 | 8.8 | 0.005e |
| Sex (% men) | 74.5 | 78.5 | 71.6 | 65.5 | 58.6 | 0.001e | 76.2 | 63.7 | 65.6 | 55.9 | <0.001e |
| Age (yr) | 65.9 | 65.9 | 66.2 | 65.7 | 66.0 | 0.78d | 65.9 | 66.3 | 65.5 | 66.2 | 0.69d |
| Lowest employment grade (%) | 7.2 | 7.1 | 5.9 | 8.1 | 9.9 | 0.02e | 6.1 | 12.8 | 12.2 | 22.1 | 0.001e |
| SF-36 MCS | 54.3 (7.7) | 56.0 (6.0) | 53.0 (8.1) | 51.0 (9.3) | 47.3 (10.7) | <0.001d | 54.7 (7.3) | 52.3 (9.3) | 51.5 (10.3) | 52.0 (9.3) | <0.001d |
| SF-36 PCS | 49.2 (8.3) | 50.6 (7.1) | 47.8 (9.2) | 46.2 (9.8) | 45.2 (10.7) | <0.001d | 49.6 (8.1) | 47.7 (9.7) | 46.1 (9.8) | 45.6 (10.0) | <0.001d |
| Current smoker (%) | 6.0 | 6.3 | 5.7 | 5.2 | 5.2 | 0.78e | 5.9 | 7.3 | 4.4 | 8.8 | 0.56e |
| High alcohol intake | 14.8 | 14.4 | 16.0 | 14.5 | 16.0 | 0.77e | 15.1 | 11.5 | 16.7 | 13.2 | 0.47e |
| BMI (kg/m2) | 26.5 (4.2) | 26.3 (4.1) | 26.8 (4.2) | 27.2 (4.5) | 27.1 (4.8) | <0.001d | 26.4 (4.2) | 27.4 (4.4) | 27.1 (4.7) | 28.0 (5.0) | <0.001d |
| Sleeping tablets | 1.2 | 0.5 | 1.7 | 2.9 | 4.3 | <0.001f | 1.0 | 2.6 | 4.4 | 1.5 | 0.008f |
| Anti-depressants | 5.9 | 3.6 | 7.3 | 11.3 | 15.5 | <0.001f | 5.3 | 12.8 | 5.6 | 5.9 | <0.001f |
| Steroid medication | 3.4 | 3.1 | 2.9 | 4.2 | 6.0 | 0.09f | 3.4 | 2.1 | 3.3 | 7.4 | 0.22f |
BMI; body mass index; SF-36 (MCS), Short Form Health Survey mental well-being component scores; SF-36 (PCS), Short Form Health Survey physical component scores.
a
Number of times high level of insomnia symptoms reported.
b
Number of times short sleep reported.
c
Kruskal–Wallis test.
d
ANOVA.
e
Chi squared test.
f
Fisher’s exact test.