Light at night and breast cancer risk: results from a population-based case-control study in Connecticut, USA

Cancer Causes Control. 2010 Dec;21(12):2281-5. doi: 10.1007/s10552-010-9653-z. Epub 2010 Oct 7.


Objective: To investigate the potential association between domestic exposure to light at night (LAN) and the risk of human breast cancer.

Methods: A case-control study of female breast cancer was conducted in Connecticut. A total of 363 incident breast cancer cases and 356 age frequency-matched controls were interviewed using a standardized, structured questionnaire to obtain information on sleeping patterns and bedroom light environment. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated by unconditional multivariate logistic regression.

Results: A non-significantly increased risk of breast cancer was observed among postmenopausal women for those keeping lights on while sleeping (OR = 1.4, 95% CI 0.7, 2.7), those who reported mainly sleeping in the daytime (OR = 1.4, 95% CI 0.5, 4.3), and those not drawing the curtains/window shades while sleeping at night (OR = 1.2, 95% CI 0.8, 1.9).

Conclusion: The results from this study suggest a potential increased risk of breast cancer associated with domestic exposure to LAN. Further studies with larger sample size are needed to confirm the results.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Breast Neoplasms / epidemiology
  • Breast Neoplasms / etiology*
  • Carcinoma / epidemiology
  • Carcinoma / etiology*
  • Case-Control Studies
  • Circadian Rhythm / physiology
  • Connecticut / epidemiology
  • Female
  • Humans
  • Light* / adverse effects
  • Middle Aged
  • Population
  • Risk Factors
  • Surveys and Questionnaires
  • United States / epidemiology
  • Work Schedule Tolerance / physiology