Table 2.

Breast cancer HRs and 95% CIs by sleep duration category as reported in 1986

Person-yearsNo. incident cases of breast cancerAge-adjusted HR (95% CI)Multivariate HR * (95% CI)
≤5 h52,4221740.88 (0.75-1.03)0.93 (0.79-1.09)
6 h295,7311,0510.96 (0.89-1.04)0.98 (0.91-1.06)
7 h 479,1301,7521.001.00
8 h272,3451,0571.05 (0.97-1.13)1.05 (0.97-1.13)
≥9 h53,4491890.95 (0.82-1.10)0.95 (0.82-1.11)
Ptrend 0.070.18
  • * Adjusted for age (months), body mass index (<20, 20-22, 23-24, 25-26,27-29, 30-34, 35-39, ≥39 kg/m2), height (<58, 58-61, 61-63, 63-66, 66-68, ≥68 inches), history of benign breast disease (yes/no), family history of breast cancer (yes/no), parity and age at first birth (nulliparous; 1-2 births and <25, 25-30, or ≥30 years at first birth; 2-3 births and <25, 25-30, or ≥30 years at first birth; >4 births and <25 or ≥25 years at first birth), age at menarche (<11, 11-13, 13-16, ≥16 years), age at menopause (premenopausal, dubious menopause, <45, 45-49, 50-54, or >54 years at menopause), postmenopausal hormone use (premenopausal, dubious menopause, never hormone replacement therapy user, past hormone replacement therapy user <5 or ≥5 years, current hormone replacement therapy user <5 or ≥5 years), physical activity (<2, 2-6, 7-17, or >17 METs/week), alcohol and caloric intake (quintiles), and smoking (never smoker, past <45, 45-99, or ≥99; current <45, 45-99, or ≥99 pack-years).

  • Reference category.

  • Test for trend modeling sleep as continuous categories and calculating Wald statistic.