Sleep duration and breast cancer risk in a cohort of Finnish women, 1976 to 1996
| . | No. of women (n = 12,222) . | No. of breast cancers . | Age-adjusted HR (95% CI) . | Multivariable HR (95% CI)* . | ||||
|---|---|---|---|---|---|---|---|---|
| Sleep duration in 1975, follow-up 1976 to 1996, seven-category classification | ||||||||
| ≤4 h | 44 | 1 | 0.73 (0.10-5.32) | 0.88 (0.11-6.91) | ||||
| 5 h | 183 | 5 | 0.81 (0.32-2.03) | 0.91 (0.36-2.32) | ||||
| 6 h | 954 | 17 | 0.66 (0.40-1.11) | 0.74 (0.44-1.26) | ||||
| 7 h | 3,473 | 68 | 0.84 (0.63-1.13) | 0.81 (0.60-1.10) | ||||
| 8 h (reference) | 5,580 | 120 | 1.00 | 1.00 | ||||
| 9 h | 1,650 | 25 | 0.73 (0.48-1.13) | 0.64 (0.40-1.02) | ||||
| ≥10 h | 338 | 6 | 0.82 (0.36-1.88) | 0.65 (0.24-1.75) | ||||
| P for linear trend (categorical) | 0.51 | 0.88 | ||||||
| Sleep duration in 1975, follow-up 1976 to 1996, three-category classification | ||||||||
| ≤6 h | 1,181 | 23 | 0.74 (0.48-1.15) | 0.85 (0.54-1.34) | ||||
| 7-8 h (reference) | 9,053 | 188 | 1.00 | 1.00 | ||||
| ≥9 h | 1,988 | 31 | 0.80 (0.55-1.17) | 0.69 (0.45-1.06) | ||||
| P for linear trend (categorical) | 0.94 | 0.34 | ||||||
| Subjects with the same sleep duration in 1975 and 1981, follow-up 1976 to 1996 | ||||||||
| ≤6 h | 476 | 14 | 1.03 (0.57-1.84) | 1.10 (0.59-2.05) | ||||
| 7-8 h (reference) | 6,386 | 125 | 1.00 | 1.00 | ||||
| ≥9 h | 534 | 7 | 0.62 (0.29-1.33) | 0.28 (0.09-0.88) | ||||
| P for linear trend (categorical) | 0.31 | 0.03 | ||||||
| . | No. of women (n = 12,222) . | No. of breast cancers . | Age-adjusted HR (95% CI) . | Multivariable HR (95% CI)* . | ||||
|---|---|---|---|---|---|---|---|---|
| Sleep duration in 1975, follow-up 1976 to 1996, seven-category classification | ||||||||
| ≤4 h | 44 | 1 | 0.73 (0.10-5.32) | 0.88 (0.11-6.91) | ||||
| 5 h | 183 | 5 | 0.81 (0.32-2.03) | 0.91 (0.36-2.32) | ||||
| 6 h | 954 | 17 | 0.66 (0.40-1.11) | 0.74 (0.44-1.26) | ||||
| 7 h | 3,473 | 68 | 0.84 (0.63-1.13) | 0.81 (0.60-1.10) | ||||
| 8 h (reference) | 5,580 | 120 | 1.00 | 1.00 | ||||
| 9 h | 1,650 | 25 | 0.73 (0.48-1.13) | 0.64 (0.40-1.02) | ||||
| ≥10 h | 338 | 6 | 0.82 (0.36-1.88) | 0.65 (0.24-1.75) | ||||
| P for linear trend (categorical) | 0.51 | 0.88 | ||||||
| Sleep duration in 1975, follow-up 1976 to 1996, three-category classification | ||||||||
| ≤6 h | 1,181 | 23 | 0.74 (0.48-1.15) | 0.85 (0.54-1.34) | ||||
| 7-8 h (reference) | 9,053 | 188 | 1.00 | 1.00 | ||||
| ≥9 h | 1,988 | 31 | 0.80 (0.55-1.17) | 0.69 (0.45-1.06) | ||||
| P for linear trend (categorical) | 0.94 | 0.34 | ||||||
| Subjects with the same sleep duration in 1975 and 1981, follow-up 1976 to 1996 | ||||||||
| ≤6 h | 476 | 14 | 1.03 (0.57-1.84) | 1.10 (0.59-2.05) | ||||
| 7-8 h (reference) | 6,386 | 125 | 1.00 | 1.00 | ||||
| ≥9 h | 534 | 7 | 0.62 (0.29-1.33) | 0.28 (0.09-0.88) | ||||
| P for linear trend (categorical) | 0.31 | 0.03 | ||||||
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.