Women who are "lark" and work better at the start of the day than at the end of the day have a lower risk of at risk of breast cancer, according to a new research run by the University of Bristol presented at the NCRI Cancer Conference in 2018 [Tuesday 6 November].
A study of several hundreds of thousands of women who examined whether the way people are asleep can contribute to the development of breast cancer, also found some evidence of the causal link between longer sleep and breast cancer.
Dr. Rebecca Richmond, a researcher in the Cancer Research Epidemiology Cancer Research UK and the MRC Integration Epidemiology Unit of the University of Bristol and colleagues, summed up data from 180,215 women enrolled in the UK Biobank project and 228,951 women who were part of the genomic association a study of breast cancer conducted by the International Breast Cancer Association (BCAC), which has so far the largest collection of genetic data on women with breast cancer.
"The use of genetic variants associated with people's preference for morning or evening sleep, insanity and insomnia previously identified by three UK UK genomics studies have examined whether these sleep patterns have a causal contribution to the risk of breast cancer," she said.
The team used the method called "Mendelian Randomization," which uses genetic variants associated with possible risk factors such as sleep patterns and examines whether they are involved in the development of a disease such as breast cancer.
Mendelian randomization analysis, which included data from BCAC 122,977 cases of breast cancer and 105,974 women without disease (control), found that preference in the morning reduces the risk of breast cancer by 40% compared to the evening type (Sova's). She also found that women who slept for more than the recommended seven to eight hours had a 20% increased risk for another sleeping disorder. 
An analysis of data from UK Biobank women (2740 new cases of breast cancer and 149,064 controls) found similar results; morning priority reduced the risk of breast cancer by 48%. Mendelian randomized analysis of these data has shown that approximately one person per 100 people will have breast cancer if they have morning preferences compared to people who have evening preferences. In this study, there was less evidence of a connection with either insomnia or sleeping on the risk of breast cancer.
Dr. Richmond said, "We would like to take further steps to explore the mechanisms on which these results are based, as the estimates obtained are based on questions related to morning or evening preference rather than whether people have become or are later on. Changing your habits changes your risk of breast cancer, it may be more complicated than that.
"However, the findings of the protective effect of early preferences on breast cancer risk in our study are consistent with previous research that highlights the role of night shift work and exposure to light at night as risk factors for breast cancer.
"We also found some evidence of the causal effect of increased sleep duration and sleep breakdown on breast cancer that were assessed using objective sleep measurements obtained from motion monitors carried by approximately 85,000 UK biobanks.
"The Mendelian randomization method used in this research is particularly useful in identifying causal disease risk factors because genetic variants identified in relation to sleeping patterns are unlikely to be affected by external or environmental factors or cancer, and can therefore be used to determine the cause and effect relationships. "
Scientists believe their findings have implications for policy-makers and employers. Dr. Richmond said: "These findings have potential policy implications for influencing the sleep habits of the common population to improve health and reduce the risk of breast cancer in women."
Dr. Richmond and her colleagues plan to investigate the mechanisms that affect the effects of different sleep patterns on the risk of developing breast cancer. "We would like to use genetic data from large populations to further understand how the body's bodily disorder can contribute to the risk of breast cancer," she said.
Ms. Cliona Clare Kirwan of Manchester University, a member of the NCRI Breast Clinical Studies Group and not involved in this research, said: "These are interesting findings that provide further evidence of how our physical clock and our natural sleep is needed at the onset of breast cancer.
"We already know that work in night shifts is associated with worse mental and physical health." This study provides further evidence suggesting that disturbed sleep patterns may play a role in the development of cancer. "The use of Mendelian randomization in this study allows researchers to examine causal effects on breast cancer of different types of sleep by looking at variations in specific genes known to be associated with sleep patterns, helping to avoid misleading conclusions that would could be affected by confused factors. "
"Examination of Causal Relationships between Sleep Characteristics and Breast Cancer Risk: Mendelian Randomization Study", published by Dr. Richmond et al. At the Cancer Conference NCRI 2018
More information Some percentages and number of cases in this press release have been updated since submitting the abstract.
The study was funded by Cancer Research UK and the Medical Research Council.
About the NCRI Cancer Conference
The NCRI Cancer Conference is the UK's largest forum to showcase the latest advances in cancer research. The conference provides a platform for researchers, clinicians, cancer sufferers and industry representatives who meet to discuss, present and demonstrate high-quality research. Informative and interactive learning courses attract more than 1,500 delegates annually and create the ideal environment for creating new contacts with key cancer research participants.
The NCRI Cancer Conference is held from 4 to 6 November 2018 at the Scottish Event Campus, Glasgow, UK.
For more information, visit https://conference.ncri.org.uk/
The National Institute for Cancer Research (NCRI) is a nationwide partnership of research institutions for cancer research, founded in 2001. Its 19 member organizations work together to accelerate advances in cancer research through co-operation to improve health and quality of life.
NCRI collaborates on cancer research, improves the quality and importance of research, and speeds up translation of research into clinical practice for the benefit of patients.
NCRI partners are: the Biotechnology and Bioscience Research Council (BBSRC); Bloodwise; Tumor brain research; Breast cancer now; Cancer Research UK; Children with Cancer UK; Department of Health and Welfare; Economic and Social Research Council (ESRC); Macmillan Cancer Support; Marie Curie; Medical Research Council (MRC); Northern Ireland Health and Social Welfare Public Health Agency (R & D department); Research fund for the treatment of pancreatic cancer; Prostate Cancer UK; Roy's Castle; Scottish Government Health Directorate (Office of the Chief Scientist); Tenovus Cancer Care; The Wellcome Trust and the Government of Wales and the Health and Care Research Wales.
For more information, visit www.ncri.org.uk