Early risers may have reduced breast cancer risk
medwireNews: Women who function better earlier in the day, so-called morning people, are less likely to develop breast cancer than those who consider themselves night owls, suggests a Mendelian randomization analysis.
As explained in a poster presented at the 2018 NCRI Conference in Glasgow, UK, the approach uses genetic variants that have a robust association with potential risk factors to assess causality, with chronotype (ie, preference for morning or evening), sleep duration, and insomnia the factors investigated in the current study.
Using self-reported data on the sleep behaviors of 156,848 participants of the UK Biobank, 7784 of whom had a breast cancer diagnosis, the investigators found an inverse but nonsignificant relationship between morning preference and breast cancer risk in a one-sample Mendelian randomization analysis. The hazard ratio (HR) was 0.85 per category increase, where the categories were defined as definite evening preference, intermediate evening preference, don’t know, intermediate morning, and definite morning preference.
The findings were statistically significant when a multivariable model adjusting for a raft of confounders was applied to the same data, with an HR of 0.95 per category increase.
And the protective effect of morning preference was also seen in a two-sample Mendelian randomization analysis of Breast Cancer Association Consortium data from 122,977 breast cancer patients and 105,974 controls, which gave a significant inverse-variance weighted odds ratio of 0.88 per category increase.
This analysis also pointed to an adverse effect of increased sleep duration, but this was not observed in either the one-sample Mendelian randomization or multivariable analyses. And there was “[l]ittle evidence for a causal effect of insomnia” in any of the analyses, the researchers noted in the poster.
Presenting author Rebecca Richmond, from the University of Bristol in the UK, told medwireNews that these results are aligned with previous epidemiologic and experimental studies that have identified night shift work and light exposure at night as potential carcinogenic factors for breast cancer.
She added that the immediate next steps now are to investigate the biology – to unpick whether the underlying mechanisms are hormonal or metabolic in nature – and to evaluate sleep behaviors as a potential causal mechanism for other cancers in which circadian disruption has been implicated, such as prostate and colorectal cancer.
Richmond concluded by stressing that the Mendelian randomization approach “doesn’t speak to genetic determinism at all, instead it highlights modifiable risk factors, which can then be impacted,” in this case chronotype and potentially sleep duration.
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