Table 1. Baseline characteristics of study subjects according to habitual sleep duration in the WHI-OS (1994–2010).
|
Sleep duration (hours per night)
|
||||||
|---|---|---|---|---|---|---|
| Characteristics (mean (s.d.) or %) | ⩽5 | 6 | 7 | 8 | ⩾9 | P -value a |
| No. of participants | 5927 | 20 267 | 28 914 | 17 293 | 3427 | |
| Prevalence (%) | 7.8 | 26.7 | 38.1 | 22.8 | 4.5 | |
| Age at baseline, years | 63.5 (7.6) | 63.3 (7.4) | 63.1 (7.3) | 63.6 (7.1) | 64.0 (7.3) | <0.001 |
| Ethnicity (%) | <0.001 | |||||
| Non-Hispanic white | 68.0 | 79.8 | 87.4 | 89.6 | 87.0 | |
| African American | 17.5 | 9.9 | 5.3 | 4.6 | 6.8 | |
| Hispanic | 6.0 | 3.9 | 3.1 | 2.9 | 4.0 | |
| Asian/Pacific island | 5.6 | 4.3 | 2.6 | 1.4 | 1.0 | |
| Other | 2.6 | 1.7 | 1.3 | 1.3 | 1.0 | |
| Missing | 0.3 | 0.4 | 0.3 | 0.2 | 0.2 | |
| Education (no college, %) | 39.6 | 31.6 | 27.7 | 28.6 | 30.8 | <0.001 |
| Employment (currently work, %) | 34.6 | 35.1 | 34.6 | 34.8 | 33.8 | 0.54 |
| Total family income ($) (%) | <0.001 | |||||
| <20,000 | 22.8 | 15.1 | 11.6 | 12.3 | 16.5 | |
| 20 000–34 999 | 23.7 | 22.6 | 20.5 | 20.8 | 21.7 | |
| 35 000–49 999 | 16.6 | 18.9 | 19.3 | 18.8 | 18.6 | |
| 50 000–74 999 | 15.3 | 18.1 | 20.3 | 19.9 | 17.9 | |
| ⩾75 000 | 13.3 | 18.2 | 21.7 | 20.6 | 17.3 | |
| Missing/do not know | 8.3 | 7.1 | 6.6 | 7.6 | 11.5 | |
|
Lifestyle factors
| ||||||
| Never smokers (%) | 50.7 | 49.9 | 50.0 | 50.4 | 49.9 | 0.77 |
| Years of smoking in smokers | 0.56 | |||||
| <20 | 21.2 | 21.8 | 21.5 | 21.6 | 22.0 | |
| ⩾20 | 25.2 | 25.7 | 26.0 | 25.2 | 25.6 | |
| Never smoked and missing | 53.6 | 52.5 | 52.5 | 53.2 | 52.5 | |
| No. of cigarettes smoked per day | 0.53 | |||||
| <15 | 10.6 | 11.2 | 10.6 | 10.5 | 10.6 | |
| 15–24 | 14.7 | 15.0 | 14.9 | 14.7 | 15.5 | |
| ⩾25 | 20.8 | 21.0 | 21.6 | 21.1 | 20.8 | |
| Never smoked and missing | 53.9 | 52.8 | 52.9 | 53.7 | 53.1 | |
| Alcohol (serving per week) | 2.3 (4.7) | 2.4 (4.8) | 2.4 (4.8) | 2.4 (4.7) | 2.4 (5.2) | 0.89 |
| Physical activityb | 12.3 (13.7) | 12.5 (13.5) | 12.5 (13.9) | 12.3 (13.6) | 11.9 (13.2) | 0.08 |
| Waist to hip ratio | 0.8 (0.1) | 0.8 (0.1) | 0.8 (0.1) | 0.8 (0.1) | 0.8 (0.1) | 0.74 |
| Body mass index, kg m−2 | 27.9 (5.9) | 28.0 (5.9) | 27.9 (5.9) | 27.9 (5.9) | 28.0 (5.8) | 0.71 |
| Total energy intake, kcal | 1613 (707) | 1632 (730) | 1624 (704) | 1621 (744) | 1609 (698) | 0.14 |
|
Medical history and medication (yes, %)
| ||||||
| Screening colonoscopy | 48.8 | 49.1 | 48.9 | 48.7 | 48.9 | 0.98 |
| Colorectal polyps removed | 9.33 | 8.76 | 8.83 | 8.47 | 8.61 | 0.79 |
| Ulcerative colitis | 1.21 | 1.18 | 1.00 | 1.13 | 1.08 | 0.34 |
| Treated type 2 diabetes | 4.13 | 4.27 | 4.59 | 4.57 | 4.29 | 0.36 |
| Cardiovascular diseases | 16.1 | 17.0 | 16.7 | 16.9 | 16.2 | 0.74 |
| Hypertension | 34.2 | 33.7 | 33.8 | 33.4 | 32.6 | 0.20 |
| First-degree family history of CRC | 14.9 | 15.2 | 15.1 | 15.4 | 14.9 | 0.90 |
| Use of NSAIDs | 19.6 | 19.2 | 19.3 | 19.0 | 18.4 | 0.56 |
|
Frequency of sleep habits (⩾3 times per week, %)
| ||||||
| Use of sleeping pill | 9.13 | 9.08 | 9.18 | 8.64 | 9.31 | 0.66 |
| Fall asleep during quiet activity | 37.9 | 30.4 | 23.7 | 20.3 | 24.1 | <0.001 |
| Nap during the day | 16.6 | 12.9 | 12.4 | 13.6 | 19.1 | <0.001 |
| Trouble falling sleeping | 34.4 | 12.7 | 5.19 | 3.64 | 5.78 | <0.001 |
| Wake up several times | 65.0 | 43.6 | 34.3 | 33.1 | 36.8 | <0.001 |
| Wake up earlier than planned | 49.4 | 25.7 | 13.0 | 8.01 | 8.11 | <0.001 |
| Trouble getting back to sleep | 47.8 | 21.8 | 9.20 | 5.27 | 5.25 | <0.001 |
| Very restless sleep | 14.2 | 2.13 | 0.57 | 0.43 | 1.08 | <0.001 |
| Snoring | 16.2 | 15.0 | 14.4 | 15.8 | 18.5 | <0.001 |
|
Psychosocial factors (%)
| ||||||
| Depression (CES-D>0.06)c | 24.0 | 13.1 | 7.95 | 7.11 | 12.6 | <0.001 |
| More fatigue (score⩽65)d | 65.9 | 52.5 | 46.0 | 44.9 | 56.7 | <0.001 |
| More pain (score<75) (%)e | 47.3 | 34.6 | 29.2 | 28.6 | 35.5 | <0.001 |
| More social strain (score >10)f | 13.9 | 9.04 | 6.36 | 5.83 | 6.70 | <0.001 |
| Care giving ⩾3 times per week | 12.1 | 9.67 | 8.44 | 8.00 | 9.00 | <0.001 |
|
Reproductive factors (%)
| ||||||
| Pregnant ever | 90.7 | 90.6 | 90.4 | 90.5 | 90.8 | 0.47 |
| Oral contraceptive ever use | 41.8 | 42.0 | 41.3 | 41.2 | 41.5 | 0.78 |
| Age at menopause, year | 47.9 (6.5) | 48.1 (6.4) | 48.1 (6.4) | 48.0 (6.4) | 48.2 (6.5) | 0.23 |
| Hormone replacement therapy | 0.05 | |||||
| Never | 33.2 | 32.4 | 32.4 | 32.9 | 31.1 | |
| Former user | 22.8 | 21.9 | 22.4 | 22.9 | 24.0 | |
| Current user | 41.1 | 42.8 | 42.3 | 41.3 | 42.5 | |
Abbreviations: CES-D=Center for Epidemiologic Studies Depression Scale; CRC=colorectal cancer; NSAIDs=nonsteroidal anti-inflammatory drugs; WHI-OS=Women’s Health Initiative–Observational Study.
a
P-value for χ2 test or analysis of variance.
b
Metabolic equivalent of task (hour per week): total energy expenditure from moderate and vigorous recreational physical activity.
c
Depression (CES-D ranges from 0 to 1). A higher score indicates a greater likelihood of depression. Center for Epidemiologic Studies Depression Scale >0.06 was used to indicate depression.
d
Fatigue score (ranges from 0 to 100). A higher score indicates less fatigue.
e
Pain score (ranges from 0 to 100). A higher score indicates a more favourable condition.
f
Social strain score (ranges from 4 to 20). A higher score indicates more strain.