Table 1 Baseline characteristics of study subjects according to habitual sleep duration in the WHI-OS (1994–2010)

From: Sleep duration and incidence of colorectal cancer in postmenopausal women

 

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

 
  1. 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.
  2. aP-value for χ2 test or analysis of variance.
  3. bMetabolic equivalent of task (hour per week): total energy expenditure from moderate and vigorous recreational physical activity.
  4. cDepression (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.
  5. dFatigue score (ranges from 0 to 100). A higher score indicates less fatigue.
  6. ePain score (ranges from 0 to 100). A higher score indicates a more favourable condition.
  7. fSocial strain score (ranges from 4 to 20). A higher score indicates more strain.
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