Table 2.
Comparison of baseline characteristics according to different nighttime sleep duration.
| Baseline Characteristics | Nighttime Sleep Duration (h/day) | |||
|---|---|---|---|---|
| ≤4 | 4–6 | 6–8 | >8 | |
| N | 544 | 897 | 957 | 222 |
| Demographic and lifestyle factors | ||||
| Mean age (years) * | 67.4 (5.9) | 66.8 (5.9) | 66.5 (5.5) | 67.7 (6.0) |
| Gender, n (%) * | ||||
| Male | 228 (41.9%) | 469 (52.3%) | 521 (54.4%) | 119 (53.6%) |
| Female | 316 (58.1%) | 428 (47.7%) | 436 (45.6%) | 103 (46.4%) |
| Education, n (%) * | ||||
| Illiterate/no formal education | 384 (70.6%) | 479 (53.4%) | 513 (53.7%) | 137 (61.7%) |
| Primary school | 109 (20.0%) | 238 (26.5%) | 282 (29.5%) | 57 (25.7%) |
| Middle school or above | 51 (9.4%) | 180 (20.1%) | 161 (16.8%) | 28 (12.6%) |
| Race, n (%) * | ||||
| Han ethnicity | 496 (95.2%) | 822 (95.1%) | 869 (94.0%) | 192 (90.1%) |
| Other minorities | 25 (4.8%) | 42 (4.9%) | 55 (6.0%) | 21 (9.9%) |
| Area of residence, n (%) * | ||||
| Urban | 401 (73.7%) | 572 (63.8%) | 653 (68.2%) | 172 (77.5%) |
| Rural | 143 (26.3%) | 325 (36.2%) | 304 (31.8%) | 50 (22.5%) |
| Current marital status, n (%) * | ||||
| Not married | 110 (20.2%) | 143 (15.9%) | 141 (14.7%) | 58 (26.1%) |
| Married or cohabitated | 434 (79.8%) | 754 (84.1%) | 816 (85.3%) | 164 (73.9%) |
| Ever smoker, n (%) * | 213 (39.2%) | 383 (42.7%) | 445 (46.5%) | 101 (45.5%) |
| Ever drinker, n (%) * | 219 (40.3%) | 408 (45.5%) | 424 (44.4%) | 106 (47.7%) |
| Mean daytime napping (hour) * | 0.49 (0.03) | 0.63 (0.02) | 0.77 (0.03) | 0.79 (0.06) |
| Clinical/biochemical measures | ||||
| BMI (kg/m2) | 22.5 (3.7) | 22.8 (3.8) | 23.0 (3.5) | 22.6 (3.6) |
| Obesity, n (%) | 36 (7.3%) | 68 (8.3%) | 73 (8.3%) | 15 (7.5%) |
| Waist circumference (cm) | ||||
| Male * | 81.9 (9.0) | 83.8 (9.7) | 84.4 (9.4) | 84.5 (9.3) |
| Female | 84.6 (10.1) | 85.8 (10.5) | 85.7 (10.4) | 85.2 (9.9) |
| Central obesity, n (%) | 179 (36.2%) | 321 (39.8%) | 353 (40.5%) | 83 (41.1%) |
| Systolic BP (mmHg) | 133.7 (23.4) | 133.0 (22.7) | 133.1 (21.3) | 134.7 (22.6) |
| Diastolic BP (mmHg) | 75.0 (12.3) | 74.1 (11.4) | 74.4 (11.6) | 75.5 (12.4) |
| Plasma glucose (mmol/L) | 5.7 (0.8) | 5.7 (0.7) | 5.7 (0.8) | 5.7 (0.9) |
| HbA1c (%) | 5.1 (0.4) | 5.1 (0.4) | 5.1 (0.4) | 5.1 (0.4) |
| Total cholesterol (mmol/L) | 5.0 (1.0) | 5.0 (1.0) | 5.0 (1.0) | 5.1 (1.0) |
| Triglycerides (mmol/L) | 1.36 (0.9) | 1.28 (0.7) | 1.37 (0.8) | 1.30 (0.8) |
| HDL-cholesterol (mmol/L) * | 1.4 (0.4) | 1.4 (0.4) | 1.3 (0.4) | 1.4 (0.4) |
| LDL-cholesterol (mmol/L) | 3.1 (0.9) | 3.1 (0.9) | 3.1 (0.9) | 3.1 (0.9) |
| Outcomes | ||||
| DM, n (%) | 87 (16.0%) | 109 (12.2%) | 125 (13.1%) | 37 (16.7%) |
Abbreviation: BMI: body mass index; BP: blood pressure; HbAlc: hemoglobin A1c; HDL: high-density lipoprotein; LDL: low-density lipoprotein; DM: diabetes mellitus. Data were reported as mean (SD) or number (percentage). * p < 0.05 for difference.