A study, recently presented at the NCRI 2018 Conference (4–6 November, Glasgow, Scotland), has demonstrated that women who function better at the beginning of the day than the end of the day (larks) could have a lower of risk breast cancer.
The study analyzed data from approximately 180,000 women who had been enrolled in the BioBank project and around 228,000 women who had been part of a genome-wide association study of breast cancer conducted by the international Breast Cancer Association Consortium (BCAC – 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,” explained Rebecca Richmond (University of Bristol, UK).
By utilizing Mendelian randomization analysis, which included data from BCAC of 122,977 cases of breast cancer and 105,974 women without the disease (the controls), the team of researchers demonstrated that a preference for mornings reduced the risk of breast cancer by 40% compared with being an evening type.
It also found that women who slept longer than the recommended 7–8 hours had a 20% increased risk of the disease per additional hour slept.
Analysis of data obtained from the UK Biobank women (2,740 new cases of breast cancer and 149,064 controls), found similar results; morning preference reduced the risk of breast cancer by 48%.
Mendelian randomization analysis of these data revealed that approximately one less person per 100 will develop breast cancer if they have a morning preference compared to people who have an evening preference. There was less evidence of an association with either insomnia or sleep duration on risk of breast cancer in this study.
Richmond commented: “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. In other words, it may not be the case that changing your habits changes your risk of breast cancer; it may be more complex than that.”
Richmond and her colleagues are planning to investigate the mechanisms underlying the effects of different sleep characteristics on the risk of developing breast cancer.
“We would like to use genetic data from large populations to further understand how disrupting the body’s natural body clock can contribute to breast cancer risk,” Richmond concluded.