Table 1.
Demographic and health variables according to sleep duration
| Sleep duration |
||||
|---|---|---|---|---|
| Demographic | Twin Sample (n = 1,224) | 7 hours (n = 306) | 7–8.9 hours (n = 807) | ≥ 9 hours (n = 111) |
| Age, mean years | 36.9 (15.0) | 38.6 (14.4) | 36.3 (14.9) | 36.4 (17.3) |
| Female, % | 69 | 64 | 70 | 72 |
| White, %† | 92 | 89 | 94 | 91 |
| Cohabiting*, % | 51 | 45 | 52 | 59 |
| Children living in home, % | ||||
| None | 73 | 70 | 73 | 82 |
| 1–2 | 22 | 23 | 22 | 15 |
| ≥ 3 | 5 | 6 | 5 | 3 |
| Health | ||||
| Smoker, % | 16 | 23 | 14 | 12 |
| Alcoholic drinks/day‡, % | ||||
| None | 16 | 15 | 16 | 20 |
| 1–2 | 58 | 56 | 60 | 53 |
| 3–4 | 17 | 18 | 17 | 16 |
| ≥ 5 | 9 | 12 | 7 | 10 |
| Chronic disease¥, % | 5 | 8 | 3 | 8 |
†
Race was defined as white or nonwhite;
*
Cohabitation included twins that were married or living with a partner;
‡
Drinks of alcoholic beverages consumed on a typical day when the twin was drinking;
¥
Chronic disease included twins with any of the following: type I or II diabetes mellitus, stroke, or heart disease (e.g., heart attack, angina, bypass surgery)