Table 2. Characteristics of subjects in the 2007 wave according to sleep duration categorya (n = 1687).
| Overall | Self-reported sleep duration at the 2007 wave (hours) | P valueb | |||||
| ≤4 | 5 | 6 | 7 | ≥8 | |||
| Number of subjects (% of overall) | 1687 (100) | 66 (3.9) | 448 (26.6) | 852 (50.5) | 277 (16.4) | 44 (2.6) | |
| Age (years) | 33.4 (5.0) | 33.1 (4.6) | 33.4 (5.2) | 33.4 (4.9) | 33.8 (5.0) | 32.7 (5.0) | 0.550 |
| BMI (kg/m2) | 23.5 (3.3) | 24.2 (3.8) | 24.0 (3.7) | 23.2 (3.0) | 23.3 (3.0) | 23.6 (2.8) | 0.000 |
| Obesity (BMI of ≥25.0 kg/m2) (%) | 26.6 | 33.3 | 33.5 | 22.9 | 24.2 | 34.1 | 0.000 |
| Drinking habit (%) | 84.4 | 90.9 | 82.1 | 85.6 | 83.0 | 81.8 | 0.255 |
| Alcohol (g/week) | 114.6 (116.9) | 117.3 (100.9) | 109.9 (114.2) | 112.1 (114.8) | 126.4 (127.4) | 133.2 (136.1) | 0.000 |
| Exercise habit (%) | 48.1 | 36.9 | 47.0 | 47.1 | 54.4 | 57.1 | 0.050 |
| Smoking habit (%) | 40.8 | 43.9 | 44.6 | 38.6 | 40.4 | 41.9 | 0.316 |
| Psychiatric medication (%) | 0.2 | 0.0 | 0.0 | 0.1 | 0.7 | 0.0 | 0.215 |
| Depressive symptoms (%) | 5.3 | 7.6 | 9.0 | 3.8 | 4.0 | 2.3 | 0.001 |
| Ill health (%) | 2.5 | 4.6 | 3.6 | 2.0 | 1.4 | 4.6 | 0.187 |
| Sleep disturbance (%) | 3.2 | 10.8 | 4.7 | 2.1 | 2.5 | 0.0 | 0.000 |
| Midmorning sleepiness (%) | 3.6 | 10.6 | 5.2 | 2.8 | 2.2 | 0.0 | 0.002 |
| Midmorning fatigue (%) | 4.5 | 9.1 | 6.7 | 3.4 | 3.6 | 2.3 | 0.020 |
BMI, body mass index.
aData are expressed as means (standard deviation) or percentages. Each percentage was calculated without missing data.
bP value: comparison across waves using analysis of variance for means and the chi-square test for proportions.