Table 3.

Insufficient sleep and breast cancer risk in a cohort of Finnish women, 1982 to 1996

Insufficient sleep in 1981Hours of sleep, mean (median)No. of women (n = 10,844)No. of breast cancersAge-adjusted HR (95% CI)Multivariable HR (95% CI) *
No lack of sleep (<1 h, reference)7.8 (8.0)8,5321381.001.00
Lack of sleep ≥1 h7.1 (7.0)2,312411.17 (0.82-1.67)1.19 (0.84-1.70)
1 h increase in lack of sleep (0-4 h)7.6 (7.5)9,0421441.11 (0.86-1.43)1.12 (0.87-1.45)
  • * 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.