The study of several hundred thousand women, which was investigating whether the way people sleep can contribute to the development of breast cancer, also found some evidence for a causal link between sleeping for longer and breast cancer.
Dr Rebecca Richmond, from Bristol, said: 'We would like to do further work to investigate the mechanisms underpinning these results, as the estimates obtained are based on questions related to morning or evening preference rather than actually whether people get up earlier or later in the day.
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.
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.
University of Manchester's Cliona Clare Kirwan, a member of the NCRI Breast Clinical Studies Group, did not take part in the research but said it provided "further evidence of how our body clock and our natural sleep preference is implicated in the onset of breast cancer".
The second analysis, using self-reported data on sleep from 180,000 participants, showed a similar trend of early rising women having a 40% lower risk of breast cancer.
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That's according to European researchers looking at International Genetic Data.
Out of the 400 000 women, 2,740 were breast cancer survivors and 149 064 were disease free.
Richmond stressed that the 48% lower risk was identified among "extreme" cases, where people identified themselves as "definite" morning people out of the five categories they could chose from - definite morning, more morning than evening, neither, more evening than morning, definite evening.
There are theories around the causes of sleep's effect on cancer, she said, such as the idea that artificial light at night leads to hormonal disruption.
The Chief Executive Officer, AXA Mansard Health Limited, Mr Tope Adeniyi, said, "There is still no sure way to prevent breast cancer yet". The World Health Organization already says disruption to people's body clocks because of shift work is probably linked to cancer risk.
About the NCRI Cancer ConferenceThe NCRI Cancer Conference is the UK's largest forum showcasing the latest advances in cancer research.