Table 2.

Age-adjusted characteristics of the study population at 2001 baseline by sleep duration

Variables
Amount of sleep over a 24-hour period (hours)	≤6	7	8	≥ 9
Proportion of sample (%)	29	43	23	5
Age, yearsa	46.92 ± 4.57	46.66 ± 4.66	46.61 ± 4.70	46.44 ± 4.68
Body Mass Index, kg/m2	26.62 ± 5.29	25.89 ± 4.96	25.77 ± 4.91	26.39 ± 5.24
Physical activity, MET-hours/weekb	19.69 ± 22.89	19.88 ± 21.64	20.35 ± 22.23	16.83 ± 20.83
Alcohol intake, g/day	3.57 ± 6.86	4.01 ± 6.84	4.35 ± 7.70	4.33 ± 8.66
Alternate Health Eating Indexc	47.18 ± 10.68	47.91 ± 10.62	48.23 ± 10.82	47.49 ± 11.06
Rotating night shift work, ≥10 years, %	12	7	6	7
First degree relative history of melanoma, %	12	11	11	13
Red or blonde hair, %	19	20	20	21
Moles, ≥ 10 on lower legs, %	14	15	15	15
Artificial tanning, ≥ 6 times/year at ages 25-35, %	3	3	3	3
Time spent in sun, ≥ 5 hours/week at ages 25-35, %	43	44	44	45
Severe sunburns, ≥ 6 at ages 15-20, %	10	10	10	11
Skin sensitivity to burningd, %	41	42	40	42
Annual UV-B flux at residence, ≥ 145 R-B unitse, %	20	22	24	26
Sleep not usually adequate, %	81	48	18	21
Sleepy ≥4 days/week, %	18	10	8	21
Snore most nights, %	17	15	15	20
Restless legs syndrome	3	2	2	4
Current smoker, %	11	8	7	8
Married, %	75	81	83	78
In top 20 percent of economic ladderf, %	8	12	14	13
Oral contraceptive use, ≥ 8 years, %	23	22	21	22
Current use of postmenopausal hormonesg, %	60	66	65	69

Values are means ± SD or percentages and are standardized to the age distribution of the study population

^aValue is not age-adjusted

^bMetabolic equivalents from recreational and leisure-time activities

^cScore of 0-100 measuring adherence to a dietary pattern most predictive of disease risk

^dSkin reaction after two or more hours in the sun without sunscreen on a bright sunny day during childhood and adolescence

^eMeasured in Robertson-Berger units (count×10⁻⁴)

^fSelf-reported economic status compared to others

^gCalculated among postmenopausal women only