Women who self-reported sleeping more than the average seven to eight hours per night were also found to have a slightly increased risk of breast cancer, of 20% per extra hour slept, according to the team's Mendelian randomization analysis.
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.
Researchers also looked at results from nearly 229,000 women signed up to an global genetic study carried out by the Breast Cancer Association Consortium.
In total, 341 variants linked to circadian rhythm and no other known risk factors for cancer (for example, obesity) were analyzed.
Cases from the BCAC had a 40 percent reduction among morning people and it was 48 percent in the U.K. Biobank.
Cancer risks associated with a person's body clock and sleep patterns have been reported in previous research and the United Kingdom researchers wanted to explore sleep traits in more detail, as well as any genetic factors underlying this.
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Richmond 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".
"These intriguing results add to the growing body of evidence that there is some overlap between the genetics of when we'd prefer to sleep and our breast cancer risk, but more research is required to unravel the specifics of this relationship", he said.
However, Dr Richmond pointed out that the possible protective effect of being a morning person on breast cancer risk was in keeping with previous research showing that working night shifts and "light-at-night" exposure increased the risk of breast cancer.
She said policy-makers and employers should take note of the research. Dr Richmond said: "These findings have potential policy implications for influencing sleep habits of the general population in order to improve health and reduce the risk of breast cancer among women".
"We know already that night shift work is associated with worse mental and physical health".
However, cancer experts say modifying your sleep patterns probably won't have a significant impact on your cancer risk. "This helps to avoid misleading conclusions that could have been affected by confounding factors".
The NCRI Cancer Conference is taking place from 4-6 November 2018 at the Scottish Event Campus, Glasgow, UK. Still more studies must be done to understand the connection between waking up earlier or later in the day and breast cancer diagnosis.