Table 1.
Baseline characteristics, overall and by frequency of nightmares.
| Variable | Total | Nightmares |
P-value for difference between groups | ||
|---|---|---|---|---|---|
| Often, always | Sometimes | Never, seldom | |||
| N | 40,902 | 407 | 7496 | 32,999 | |
| Mean age (SD) | 51.2 (16.0) | 50.0 (19.1) | 50.5 (16.7) | 51.4 (15.7) | 0.003 |
| Women, n (%) | 26,301 (64) | 291 (72) | 5489 (73) | 20,521 (62) | <0.001 |
| University degree, n (%) | 11,534 (28) | 88 (22) | 1815 (24) | 9631 (29) | <0.001 |
| Working, n (%) | 20,274 (50) | 138 (34) | 3388 (45) | 16,748 (51) | <0.001 |
| Retired, n (%) | 10,603 (26) | 128 (31) | 1928 (26) | 8547 (26) | 0.036 |
| Student, n (%) | 1604 (3.9) | 37 (9.1) | 415 (5.5) | 1152 (3.5) | <0.001 |
| Unemployed, n (%) | 821 (2.0) | 15 (3.7) | 184 (2.5) | 622 (1.9) | <0.001 |
| Long-term sick-leave, n (%) | 670 (1.6) | 21 (5.2) | 197 (2.6) | 452 (1.4) | <0.001 |
| Other, n (%) | 1850 (4.5) | 30 (7.4) | 359 (4.8) | 1461 (4.4) | 0.038 |
| Difficulty falling asleep, n (%) | 2243 (5.5) | 131 (32) | 701 (9.4) | 1411 (4.3) | <0.001 |
| Difficulty maintaining sleep, n (%) | 2922 (7.1) | 136 (33) | 897 (12) | 1889 (5.7) | <0.001 |
| Early morning awakening, n (%) | 3550 (8.7) | 117 (29) | 950 (13) | 2483 (7.5) | <0.001 |
| Tired at awakening, n (%) | 5934 (15) | 142 (35) | 1526 (20) | 4266 (13) | <0.001 |
| Daytime sleepiness, n (%) | 2955 (7.2) | 129 (32) | 884 (12) | 1942 (5.9) | <0.001 |
| Insomnia, n (%) | 2350 (5.8) | 127 (31) | 748 (10) | 1475 (4.5) | <0.001 |
| Mean sleep duration, hours/night (SD) | 6.8 (1.0) | 6.4 (1.4) | 6.8 (1.1) | 6.9 (1.0) | <0.001 |
| Often/always depressive symptoms, n (%) | 2565 (6.3) | 142 (35) | 942 (13) | 1481 (4.5) | <0.001 |
| Often/always anxiety symptoms, n (%) | 3785 (9.4) | 156 (39) | 1367 (19) | 2262 (7.0) | <0.001 |
| Current smokers, n (%) | 2957 (7.2) | 50 (12) | 742 (9.9) | 2165 (6.6) | <0.001 |
| Past smokers, n (%) | 10,506 (26) | 92 (23) | 1917 (26) | 8497 (26) | 0.340 |
| BMI, kg/m2 (SD) | 24.6 (3.5) | 25.1 (4.1) | 24.7 (3.8) | 24.6 (3.5) | 0.025 |
| Low physical activity, n (%) | 6492 (16) | 101 (25) | 1227 (16) | 5164 (16) | <0.001 |
| Coffee, no of cups/daily (SD) | 2.9 (1.8) | 2.6 (1.9) | 2.8 (1.8) | 2.9 (1.8) | <0.001 |
| Alcohol drinkers, n (%) | 36,011 (88) | 351 (86) | 6595 (88) | 29,065 (88) | 0.516 |
| Standard glasses of alcohol per week (SD) | 6.3 (4.3) | 6.0 (4.5) | 6.1 (4.3) | 6.3 (4.3) | <0.001 |
| Cancer, n (%) | 2558 (6.3) | 35 (8.6) | 538 (7.2) | 1985 (6.0) | <0.001 |
| Cardiovascular disease, n (%) | 4458 (11) | 81 (20) | 939 (13) | 3438 (11) | <0.001 |
Differences in baseline variables across categories of nightmare frequency were assessed using one-way analysis of variance (ANOVA) for continuous variables and the Kruskal–Wallis test for categorical variables.