The scientists, led by the University of Bristol, also showed women who slept longer than the recommended seven to eight hours a night increased their chances of a diagnosis by 20 per cent for each extra hour spent asleep.
Women who like to wake up earlier have almost half the risk of breast cancer as their night owl counterparts, according to a study presented by British scientists on Tuesday. The use of Mendelian randomisation in this study enables the researchers to examine the causal effect on breast cancer of different sleep patterns by looking at the variations in particular genes already known to be associated with sleep characteristics.
Cases from the BCAC had a 40 percent reduction among morning people and it was 48 percent in the U.K. Biobank.
Led by Dr Rebecca Richmond at the University of Bristol, UK, along with the University of Manchester, the University of Exeter, and USA and Norwegian researchers, the large-scale study looked at data from taken from 409,166 women to investigate how a person's preference for mornings or evenings as well as their sleep habits may contribute to the development of breast cancer.
They also found some evidence for a causal effect of increased sleep duration and sleep fragmentation on breast cancer.
The research - which was presented Tuesday at the National Cancer Research Institute Conference in Glasgow - adds to previous findings suggesting women who work night shifts or sleep in brighter environments have a higher risk of developing cancer.
She said policy-makers and employers should take note of the research.
"While these intriguing results highlight the need for further investigation, changing your sleeping habits is not as easily done as other proven risk-reducing choices, as they're often part and parcel with jobs, parenting, or other health conditions", Dr. Emma Pennery, clinical director at Breast Cancer Care, told The Independent.
"We know that sleep is important generally for health", said Richmond.
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". "This helps to avoid misleading conclusions that could have been affected by confounding factors".
About the NCRI Cancer ConferenceThe NCRI Cancer Conference is the UK's largest forum showcasing the latest advances in cancer research. And obesity is set to become the leading preventable cause of breast cancer for women in the United Kingdom, according to a report from earlier this year.