Table 1. Baseline characteristics of the subjects according to sleep duration.
| Sleep duration | ⩽6 | 7–8 | ⩾9 |
|---|---|---|---|
| Number of subjects | 2671 | 15 127 | 4522 |
| Mean age, s.d. (years) | 57.7 (11.0) | 58.0 (10.4) | 64.0 (9.3) |
| Mean body mass index, s.d. (kg m−2) | 23.7 (3.2) | 23.4 (2.9) | 23.1 (3.4) |
| Having history of diseasesa (%) | 31.3 | 29.4 | 38.9 |
| Employed (%) | 59.2 | 61.0 | 47.8 |
| Married (%) | 80.1 | 82.2 | 77.0 |
| Never smoked (%) | 19.4 | 18.2 | 15.9 |
| Never drank (%) | 15.5 | 16.3 | 14.8 |
| Walking 1 h per day or more (%) | 42.6 | 45.7 | 43.4 |
| Having family history of cancer (%) | 30.0 | 29.3 | 28.4 |
s.d.=standard deviation.
a
History of stroke, hypertension, myocardial infarction, or diabetes mellitus.