Table 4.

Sleep quality and breast cancer risk in a cohort of Finnish women, 1976 to 1996

No. of women (n = 12,084)No. of breast cancersAge-adjusted HR (95% CI)Multivariable HR (95% CI) *
Sleep quality in 1975, follow-up 1976 to 1996
    Good5,2451031.001.00
    Fairly good5,8031130.84 (0.64-1.10)0.84 (0.63-1.12)
    Fairly poor787160.66 (0.39-1.13)0.78 (0.45-1.35)
    Poor24980.99 (0.47-2.07)1.15 (0.54-2.43)
    P for linear trend (categorical)0.210.52
Subjects with the same sleep quality in 1975 and 1981, follow-up 1976 to 1996
    Good3,047561.001.00
    Fairly good3,270700.95 (0.67-1.35)0.91 (0.62-1.32)
    Fairly poor21950.75 (0.30-1.90)0.89 (0.35-2.27)
    Poor5831.58 (0.45-5.52)1.87 (0.52-6.73)
    P for linear trend (categorical)0.920.97
  • * Adjusted for the effects of age, zygosity, social class, number of children, use of oral contraceptives, body mass index, alcohol use, smoking, and physical activity.