Being a ‘morning person’ linked to lower risk of breast cancer

Sleeping longer than the recommended 7-8 hours a night may carry an increased risk of developing breast cancer, according to a study that used UK Biobank data and was published in the BMJ.

An international research team used Mendelian randomization to analyse genetic variants associated with three particular sleep traits to examine whether sleep traits could have a direct effect on the risk of developing breast cancer. The morning or evening preference, sleep duration, and insomnia for 180,216 women in the UK Biobank study and 228,951 women in the Breast Cancer Association Consortium study were analysed.

UK Biobank data provided some supportive evidence for a protective effect of morning preference on breast cancer risk, but imprecise estimates for sleep duration and insomnia symptoms. Analysis from BCAC revealed similar results on the effect of morning preference, and showed a potential harmful effect of longer sleep duration (more than the recommended 7-8 hours) on breast cancer.

As such, the researchers say their findings “provide strong evidence for a causal effect of chronotype on breast cancer risk.”

Further work to uncover possible reasons for the associations between sleep disruption and breast cancer is required, they add.