Nov. 6 (UPI) -- If a woman regularly wakes up early in the morning, she has up to a 48 percent lower risk of developing breast cancer, according to a study in England.
In addition, women who slept longer than seven to eight hours had a 20 percent increased risk per additional hour slept. The findings, which have not been peer-reviewed, were presented at the NCRI Cancer Conference in Glasgow, Scotland, from Sunday through Tuesday.
Researchers at the University of Bristol analyzed data from 180,215 women enrolled with the U.K. Biobank project, and 228,951 women who participated in genome-wide association study of breast cancer led by the international Breast Cancer Association Consortium.
The consortium has the largest collection of genetic data on women with breast cancer obtained so far.
"Using genetic variants associated with people's preference for morning or evening, sleep duration and insomnia, which had previously been identified by three recent UK Biobank genome-wide association studies, we investigated whether these sleep traits have a causal contribution to the risk of developing breast cancer," Dr. Rebecca Richmond, a research fellow at Cancer Research U.K. and the University of Bristol, said in a press release.
They utilized a genetic method known as Mendelian randomization in which genetic variants associated with possible risk factors, such as sleep characteristics, were analyzed.
Cases from the BCAC had a 40 percent reduction among morning people and it was 48 percent in the U.K. Biobank.
In the Mendelian randomization analysis, they found approximately one less person per 100 will develop breast cancer if they have a morning preference compared with people who have an evening preference.
The researchers said they would like to perform further work because the estimates were based on questions related to morning or evening preference rather than actually whether people get up earlier or later in the day.
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.
"The findings of a protective effect of morning preference on breast cancer risk in our study are consistent with previous research highlighting a role for night shift work and exposure to 'light-at-night' as risk factors for breast cancer," Richmond said.
She said policy-makers and employers should take note of the research.
"These are interesting findings that provide further evidence of how our body clock and our natural sleep preference is implicated in the onset of breast cancer," said Cliona Clare Kirwan, from the University of Manchester, who who was not involved in this research. "We know already that night shift work is associated with worse mental and physical health. This study provides further evidence to suggest disrupted sleep patterns may have a role in cancer development."