Association between circadian rhythm-related behaviors and breast cancer: a bidirectional Mendelian randomization study.

Feb 27, 2026Future science OA

Two-way genetic study of links between daily activity patterns and breast cancer

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Abstract

Increased sleep duration is associated with a 33% higher risk of breast cancer.

Being a morning person is linked to a lower risk of breast cancer, with a 24% reduced odds.
Waking up early is associated with a 29% reduction in breast cancer risk.
A higher risk of breast cancer is observed in patients who experience insomnia, with a slight increase in odds.
Similar protective effects of morningness and early rising are noted for estrogen receptor-positive breast cancer.

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BACKGROUND: Breast cancer (BC) is a major cause of cancer-related morbidity and mortality in women, with its development linked to circadian rhythm disruption. This study employs two-sample bidirectional Mendelian randomization (MR) to explore their causal relationship.

MATERIALS AND METHODS: Genome-wide association study (GWAS) from the MRC Integrated Epidemiology Unit (MRC IEU) on circadian rhythm-related behaviors and BC subtypes was used. Causal effects were assessed using multiple MR methods, with IVW as the primary approach. Sensitivity analyses were conducted to ensure result robustness.

RESULTS: Increased sleep duration was associated with a higher BC risk (IVW model: OR = 1.33, < 0.001), while being a morning person (IVW model: OR = 0.76, = 0.003) and getting up in the morning (IVW model: = 0.71, < 0.001) were protective factors. Similar findings were observed for estrogen receptor-positive (ER+) BC. BC patients were also more likely to experience insomnia (IVW model: OR = 1.01, < 0.001). P P OR P P

CONCLUSION: Our bidirectional MR study provides genetic evidence for a causal link between genetically predicted circadian rhythm-related behaviors and BC. These findings underscore the role of genetic factors influencing circadian biology in BC etiology and warrant further investigation into the underlying mechanisms.

Association between circadian rhythm-related behaviors and breast cancer: a bidirectional Mendelian randomization study.

Abstract

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