Women who wake up early may have a lower risk of developing breast cancer than the females sleeping for longer hours, a study has found.
Using a technique called Mendelian randomisation, researchers analysed genetic variants associated with three particular sleep traits -- morning or evening preference (chronotype), sleep duration, and insomnia.
They analysed databases of more than four lakh women from two studies -- UK Biobank study and Breast Cancer Association Consortium (BCAC) study.
After analysing UK Biobank data, the researchers concluded that morning preference was associated with a slightly lower risk of breast cancer (one less woman per 100) than evening preference, whereas there was little evidence for an association with sleep duration and insomnia symptoms.
Analysis from BCAC also supported a protective effect of morning preference, and showed a potential harmful effect of longer sleep duration (more than the recommended 7-8 hours) on breast cancer, whereas evidence for insomnia symptoms was inconsistent.
Eva Schernhammer from the University of Vienna in Austria said these findings, published in the journal BMJ, identify a need for future research exploring how the stresses on our biological clock can be reduced.