Table 4 Night waking with exposure to lighta in the year before recruitment and risk of breast cancer, by menopausal status and oestrogen receptor status of breast cancer

From: Domestic light at night and breast cancer risk: a prospective analysis of 105 000 UK women in the Generations Study

     Oestrogen-receptor status of breast cancer
  All breast cancers Positive Negative
Night waking No. cases HR (95% CI) b P -value No. cases HR (95% CI) b P -value No. cases HR (95% CI) b P -value
Total (Pyrs=640 832)
No 939 1.00   729 1.00   142 1.00  
Yes 674 1.01 (0.92–1.12) 0.82 524 1.01 (0.90–1.13) 0.90 100 1.01 (0.78–1.32) 0.91
N/k 162 1.00 (0.84–1.18) 0.99 129 1.01 (0.83–1.22) 0.93 23 1.00 (0.64–1.56) 0.99
Pre-menopausal breast cancer (Pyrs=373 323)
No 412 1.00   317 1.00   59 1.00  
Yes 247 1.10 (0.93–1.29) 0.26 188 1.09 (0.91–1.31) 0.35 39 1.24 (0.82–1.86) 0.31
N/k 31 0.63 (0.43–0.91) 0.01 25 0.64 (0.43–0.97) 0.04 5 0.81 (0.32–2.03) 0.65
Post-menopausal breast cancer (Pyrs=267 509)
No 527 1.00   412 1.00   83 1.00  
Yes 427 0.96 (0.85–1.10) 0.58 336 0.96 (0.83–1.11) 0.62 61 0.90 (0.64–1.26) 0.54
N/k 131 1.15 (0.95–1.40) 0.16 104 1.16 (0.93–1.45) 0.18 18 1.03 (0.62–1.74) 0.90
  1. Abbreviations: CI=confidence interval; HR=hazard ratio; Pyrs=person-years of follow-up.
  2. Wake and put the lights on or go into a bright room.
  3. bHazard ratios estimated using Cox proportional hazards regression with attained age as time scale, adjusted for: light at night in the year before recruitment, year of birth, history of benign breast disease, breast cancer in a first-degree relative, socioeconomic score, age at menarche, age at first birth, parity, duration of breastfeeding, oral contraceptive use, hormone replacement therapy use, menopausal status and age at menopause where applicable, pre-menopausal and post-menopausal body mass index, alcohol consumption, smoking and physical activity level.