The scientists found that those with an in-built morning preference were 40% to 48% less at risk of breast cancer. The study also found that women who sleep more than seven to eight hours have a 20% increased risk for each additional hour after that that they slept.
In other words, it is at present unknown whether it is your genetic body clock itself, or living out of sync with it - for instance, forcing yourself to get up early for work if you are a lark - which affects your breast cancer risk.
It said in a statement that the breast cancer awareness week was observed around the world in the month of October, as an annual worldwide campaign organised by major breast cancer charities to increase awareness of the disease and to raise funds for research into its cause, prevention, diagnosis, treatment and cure.
He noted they found a causal effect of increased sleep duration and sleep fragmentation on breast cancer from movement monitors worn by around 85,000 UK Biobank participants.
Being a morning person is partly down to genetics, so this lowered risk does make some sense.
"We know already that night shift work is associated with worse mental and physical health". Dr Richmond said:"These findings have potential policy implications for influencing sleep habits of the general population in order to improve health and reduce risk of breast cancer among women".
Experts not involved in the research welcomed the findings - although they cautioned that it was too early to change any behaviour until more research can be conducted.
Dipender Gill, of Imperial College London, said: "Although informative and interesting, this study alone does not warrant any action other than further investigation - people should not be changing their sleep patterns based on the evidence presented here". About 5 per cent of women with breast cancer have inherited a gene linked to the condition. According to Cancer Research UK, around a quarter of cases might be preventable.
About the NCRI Cancer ConferenceThe NCRI Cancer Conference is the UK's largest forum showcasing the latest advances in cancer research. Informative and interactive educational sessions attract over 1,500 delegates each year and create the ideal setting to establish new collaborations with key stakeholders in cancer research.
The Medifem Multi-Specialist Hospital & Fertility Centre has rounded up a series of activities put together to mark Breast Cancer Awareness campaign in October.