Table 6.
Adjusted odds ratios (95% confidence interval) of memory impairment by usual sleep duration and frequency of daytime napping
| Memory impairment |
P | |||
|---|---|---|---|---|
| N (% cases) | Adjusted OR (95% CI) | |||
| Sleep duration, hours per day | ||||
| 3–4 | 1,074 (19.0) | 1.29 (1.07–1.56) | 0.007 | |
| 5 | 2,768 (15.8) | 1.12 (0.98–1.28) | 0.09 | |
| 6 | 7,016 (13.4) | 1.00 (0.90–1.11) | 0.96 | |
| 7 | 8,598 (11.7) | Ref. | ||
| 8 | 6.734 (11.1) | 0.94 (0.84–1.04) | 0.23 | |
| 9 | 1546 (13.3) | 1.09 (0.91–1.29) | 0.34 | |
| ≥ 10 | 934 (18.2) | 1.52 (1.25–1.86) | < 0.001 | |
| P for trend (3 to7 h) | 0.005 | |||
| P for trend (7 to ≥ 10 h) | 0.003 | |||
| Daytime napping | ||||
| Never to < 1 day/week | 10,331 (12.4) | Ref. | ||
| 1–3 days/week | 4,048 (11.2) | 0.95 (0.84–1.07) | 0.38 | |
| 4–6 days/week | 2,987 (13.8) | 1.06 (0.932–1.20) | 0.39 | |
| Daily | 11,304 (13.8) | 1.07 (0.98–1.16) | 0.15 | |
| P for trend | 0.09 | |||
| Tired in the morning | ||||
| Never to < 1–2days/month | 25,411 (12.7) | Ref. | ||
| 1–2 days/week | 1,644 (13.8) | 1.18 (1.01–1.39) | 0.04 | |
| 3–4 days/week | 615 (13.8) | 1.09 (0.84–1.41) | 0.51 | |
| Almost daily | 1,000 (16.9) | 1.27 (1.05–1.53) | 0.01 | |
| P for trend | 0.003 | |||
| Insomnia | ||||
| No | 23,747 (12.8) | Ref. | ||
| Yes | 4,916 (13.5) | 1.10 (1.00–1.22) | 0.06 | |
N (% cases): total number of subjects in each group (% with memory impairment). Adjusting for age, sex, employment, occupation, education, smoking, drinking, physical activity, tea consumption, self-rated health, waist circumference, HDL- and LDL-cholesterol, fasting plasma glucose and systolic blood pressure.