"Morning person" preference tied to lower risk for breast cancer

  • Richmond RC & al.
  • BMJ
  • 26 Jun 2019

  • curated by Miriam Davis, PhD
  • Univadis Clinical Summaries
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  • Being a morning person may causally protect against breast cancer, whereas long sleep duration may heighten risk, according to a Mendelian randomization (MR) analysis of 2 large UK data sets.

Why this matters

  • Consider informing patients that certain sleep characteristics are modifiable risk factors.

Study design

  • MR analyses (which explores causal associations) of the prospective UK Biobank (n=7784 breast cancer cases) and the Breast Cancer Association Consortium (BCAC; 122,977 cases; 105,974 control individuals).
  • Sleep characteristics: chronotype (morning or evening preference), insomnia, sleep duration in multivariable regression (UK Biobank).
  • MR analysis uses single-nucleotide polymorphisms (SNPs) associated with specific sleep characteristics in genome-wide association studies (UK Biobank and BCAC).
  • Funding: NIH; others.

Key results

  • Morning vs evening preference was inversely associated with incident breast cancer in multivariable regression analysis of UK Biobank (HR, 0.95; 95% CI, 0.93-0.98/category increase).
  • In 1-sample MR analysis of UK Biobank, 341 chronotype-associated SNPs supported a protective effect of morning preference (HR, 0.85; 95% CI, 0.70-1.03/category increase).
  • In BCAC, 2-sample MR analysis supported protective effect of morning preference (OR, 0.88; 95% CI, 0.82-0.93/category increase) and an adverse effect for longer sleep duration (>8 vs 7-8 hours; OR, 1.19; 95% CI, 1.02-1.39/hour increase).
  • Insomnia unrelated to breast cancer in both databases.


  • Self-reported sleep characteristics.

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