Table 1.
Risk of post-menopausal breast cancer incidence associated with sleep characteristics and chronotype: prospective analysis in the California Teachers Study, cases diagnosed 2012–2019
| Sleep characteristic | Level | Cases (%) n = 1,085 |
Non-cases (%) n = 38,470 |
Multivariable* adjusted HR and 95% CI |
|---|---|---|---|---|
| Sleep quality | Very good | 325 (30) | 11,624 (31) | 1.00 (ref) |
| Fairly good | 587 (55) | 20,661 (54) | 1.03 (0.90, 1.19) | |
| Fairly bad or very bad | 156 (14) | 5,582 (15) | 1.02 (0.84, 1.23) | |
| Sleep latency | < 15 min | 534 (50) | 17,753 (47) | 1.00 (ref) |
| 16–30 min | 361 (34) | 13,732 (36) | 0.88 (0.76, 1.00) | |
| 31–60 min | 143 (13) | 4,817 (13) | 0.97 (0.81, 1.17) | |
| > 60 min | 35 (3) | 1,557 (4) | 0.77 (0.55, 1.09) | |
| Sleep disturbance | Not during past month | 237 (22) | 8,497 (22) | 1.00 (ref) |
| < 1 time/week | 331 (31) | 12,345 (32) | 0.97 (0.82, 1.15) | |
| 1–2 time/week | 272 (25) | 9,411 (25) | 1.04 (0.88, 1.25) | |
| ≥ 3 times/week | 229 (21) | 7,646 (20) | 1.08 (0.90, 1.30) | |
| Sleep duration | < 5 h | 30 (3) | 993 (3) | 1.08 (0.74, 1.59) |
| 5–6 h | 264 (25) | 9,296 (24) | 1.02 (0.86, 1.21) | |
| 7 h | 439 (41) | 15,812 (42) | 0.98 (0.84, 1.14) | |
| 8 h | 280 (26) | 9,807 (26) | 1.00 (ref) | |
| ≥ 9 h | 53 (5) | 1,804 (5) | 0.99 (0.73, 1.33) | |
| Sleep medication | Not during past month | 752 (70) | 26,242 (69) | 1.00 (ref) |
| < 1 time/week | 107 (10) | 4,120 (11) | 0.91 (0.74, 1.11) | |
| 1–2 time/week | 58 (5) | 2,239 (6) | 0.91 (0.69, 1.18) | |
| ≥ 3 times/week | 154 (14) | 5,093 (13) | 1.00 (0.84, 1.19) | |
| Global Sleep Index (GSI) |
Lowest scores GSI 1–4 (better sleep) |
317 (29) | 10,892 (29) | 1.00 (ref) |
| GSI 5–6 | 249 (23) | 9,282 (24) | 0.93 (0.79, 1.10) | |
| GSI 7–8 | 198 (18) | 7,356 (19) | 0.94 (0.79, 1.13) | |
|
Highest scores GSI 9–17 (worse sleep) |
281 (26) | 9,444 (25) | 1.01 (0.86, 1.19) | |
| Chronotype | Morning type/more morning than evening type | 588 (55) | 21,823 (57) | 1.00 (ref) |
| Neither morning/evening type | 131 (12) | 4,986 (13) | 0.94 (0.78, 1.14) | |
| Evening type/more evening than morning type | 343 (32) | 10,230 (27) | 1.19 (1.04, 1.36) |
Analysis for each individual sleep characteristic excluded participants who did not provide responses for all sleep questions
Analysis for the chronotype variable excluded those who did not provide a response for the chronotype question
* Risk estimates adjusted for age, race/ethnicity, BMI, and family history of breast cancer