Nighttime outdoor light shows an association with postmenopausal breast cancer incidence

  • Xiao Q & al.
  • Int J Cancer
  • 2 Jun 2020

  • curated by Miriam Davis, PhD
  • Univadis Clinical Summaries
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Takeaway

  • High exposure to nighttime residential outdoor light is associated with a 10% increase in the incidence of postmenopausal breast cancer.

Why this matters

  • Outdoor nighttime light exposure may be a risk factor for postmenopausal breast cancer possibly because of circadian disruption, these authors suggest.

Study design

  • The retrospective NIH-AARP Diet and Health Study used 1996 satellite imagery (N=186,981) to determine intensity of outdoor nighttime light exposure in relation to incident breast cancer (n=12,318), with more than 16 years of follow-up.
  • Funding: NIH.

Key results

  • The highest vs lowest quintile of exposure (1996 baseline) was associated with a 10% increase in incident breast cancer risk:
    • HR: 1.10 (95% CI, 1.02-1.18; P-trend=.002).
  • On subgroup analysis, the effect (HRs, 95% CIs) was significant with estrogen receptor (ER)-positive breast cancer:
    • 1.12 (1.02-1.24; P-trend=.007). 
  • It was not significant with ER-negative cancer:
    • 1.07 (0.85-1.34; P-trend=.66).
  • Factors associated (HRs, 95% CIs) with greater nighttime light exposure effects:
    • Age below the median of 62 years: 1.28 (1.07-1.54; P-trend=.004).
    • BMI 2: 1.28 (1.05-1.55; P-trend=.002).
    • ≥1 drinks/day: 1.46 (1.06-2.01; P-trend=.05).
    • Current smoking: 1.50 (1.06-2.13; P-trend=.02).

Limitations

  • Observational, correlational, residual confounding likely.