Table 2. Cox proportional hazard ratios (HRs) and 95% confidence intervals (CIs) for breast cancer incidence according to sleep duration in Japanese women.
|
Sleep duration (hours per day)
|
||||||
|---|---|---|---|---|---|---|
| ⩽6 | 7 | 8 | ⩾9 | P for trend* | P for trend† | |
| All-cases | ||||||
| Person-Year | 35 208 | 55 574 | 67 368 | 27 715 | ||
| Number of event | 42 | 40 | 50 | 11 | ||
| Crude HR (95% CI) | 1.66 (1.08–2.56) | 1.00 (reference) | 1.03 (0.68–1.56) | 0.55 (0.28–1.07) | 0.002 | 0.001 |
| Age-adjusted HR (95% CI) | 1.67 (1.08–2.58) | 1.00 (reference) | 1.09 (0.71–1.65) | 0.63 (0.32–1.24) | 0.006 | 0.006 |
| Multivariable HR (95% CI)a | 1.63 (1.06–2.52) | 1.00 (reference) | 1.14 (0.75–1.73) | 0.71 (0.36–1.41) | 0.03 | 0.02 |
| Multivariable HR2 (95% CI)b | 1.62 (1.05–2.50) | 1.00 (reference) | 1.14 (0.75–1.73) | 0.72 (0.36–1.43) | 0.03 | 0.03 |
| Multivariable HR3 (95% CI)c | 1.67 (1.002–2.78) | 1.00 (reference) | 0.99 (0.59–1.65) | 0.29 (0.09–0.98) | 0.002 | 0.002 |
| Stratified analysis | ||||||
| Age (P for interaction=0.48) | ||||||
| <60 years | ||||||
| Person-Years | 17 048 | 27 696 | 25 216 | 5666 | ||
| No. of cases | 26 | 21 | 22 | 2 | ||
| Multivariable HR (95% CI)b | 2.01 (1.12–3.59) | 1.00 (reference) | 1.16 (0.63–2.13) | 0.43 (0.10–1.87) | 0.02 | 0.02 |
| ⩾60 years | ||||||
| Person-Years | 18 160 | 27 878 | 42 152 | 22 049 | ||
| No. of cases | 16 | 19 | 28 | 9 | ||
| Multivariable HR (95% CI)b | 1.20 (0.61–2.35) | 1.00 (reference) | 1.09 (0.61–1.97) | 0.81 (0.36–1.82) | 0.46 | 0.48 |
| Menopausal status (P for interaction=0.70) | ||||||
| Premenopausal | ||||||
| Person-Years | 8154 | 12 907 | 9286 | 1617 | ||
| No. of cases | 11 | 8 | 9 | 0 | ||
| Multivariable HR (95% CI)b | 2.06 (0.81–5.23) | 1.00 (reference) | 1.48 (0.56–3.93) | — | 0.10 | 0.27 |
| Postmenopausal | ||||||
| Person-Years | 22 331 | 35 004 | 46 183 | 18 933 | ||
| No. of cases | 28 | 29 | 35 | 9 | ||
| Multivariable HR (95% CI)b | 1.46 (0.86–2.46) | 1.00 (reference) | 1.04 (0.63–1.70) | 0.74 (0.35–1.59) | 0.11 | 0.09 |
*P for trend values were calculated by treating sleep duration as a continuous variable.
†P for trend values were calculated by treating each categories of sleep duration as a continuous variable.
Multivariable HR was adjusted for age (continuous variable); body mass index (<18.5, 18.5–25.0, ⩾25.0 kg m−2); history of diseases (having history of stroke, hypertension, myocardial infarction, or diabetes mellitus); family history of cancer (presence or absence in first-degree relatives); job (employed or unemployed); marital status (married or unmarried); education (junior high school or less, high school, or college/university or higher); cigarette smoking (never smoker, ex-smoker, current smoker 1–19 cigarettes per day, or current smoker ⩾20 cigarettes per day); alcohol consumption (never drinker, ex-drinker, or current drinker); time spent walking (less than 1 h per day, or longer than 1 h per day).
Multivariable HR2 was adjusted for above plus total caloric intake (continuous variable, kcal day−1); menopausal status (premenopausal or postmenopausal); age at menarche (⩽13 years, 14–15 years, or ⩾16 years); age at first delivery (⩽21 years, 22–25 years, or ⩾26 years); number of deliveries (0 births, 1–2 births, or ⩾3 births); using of oral contraceptive drugs (yes or no); using of hormone drugs except for oral contraceptive drugs (yes or no).
Multivariable HR3 denotes the HR2 with cases diagnosed in the first 3 years of follow-up excluded from the analysis.