Table 2 Light at night at 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
LAN level a 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)
Low 416 1.00   330 1.00   54 1.00  
Med 847 1.00 (0.89–1.12) 0.97 661 0.99 (0.87–1.13) 0.88 134 1.20 (0.88–1.65) 0.26
High 512 1.01 (0.88–1.15) 0.92 391 0.98 (0.84–1.14) 0.78 77 1.16 (0.82–1.65) 0.40
Pre-menopausal breast cancer (Pyrs=373 323)
Low 145 1.00   115 1.00   19 1.00  
Med 326 0.91 (0.74–1.10) 0.33 250 0.89 (0.71–1.11) 0.30 53 1.09 (0.64–1.84) 0.75
High 219 1.00 (0.81–1.24) 1.00 165 0.97 (0.76–1.24) 0.82 31 1.04 (0.59–1.85) 0.89
Post-menopausal breast cancer (Pyrs=267 509)
Low 271 1.00   215 1.00   35 1.00  
Med 521 1.05 (0.91–1.22) 0.48 411 1.05 (0.89–1.24) 0.55 81 1.26 (0.84–1.87) 0.26
High 293 1.00 (0.85–1.18) 1.00 226 0.97 (0.81–1.17) 0.77 46 1.23 (0.79–1.92) 0.36
  1. Abbreviations: CI=confidence interval; HR=hazard ratio; LAN=light at night; Pyrs=person-years of follow-up.
  2. aLow: ‘Too dark to see your hand, or you wear a mask’; Med: ‘Light enough to see your hand in front of you, but not see across the room’; High: ‘Light enough to see across the room, but not read’+‘Light enough to read’.
  3. bHazard ratios estimated using Cox proportional hazards regression with attained age as time scale, adjusted for: 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.