Women who wake up early in the morning or prefer the & # 39; camel & # 39; may be less likely to have breast cancer than women who prefer evening. It appears in the majority of UK data analysis results.
The researchers combined data from more than 400,000 women from two UK genetic studies and used Mendelian randomisation (MR) analysis techniques to identify sleep characteristics and causal relationships between breast cancer.
The results of the study at the 2018 National Cancer Research Institute (NCRI) Cancer Conference show that women's morning / evening sleeping environments or chronotypes affect the risk of developing breast cancer.
Specifically, in the morning, people have an inverse relationship with breast cancer outbreaks, and researchers reported a 40-48% reduction in risk compared to evening type.
In addition, the longer the sleeping time, the lower the risk of breast cancer. Those who exceeded the recommended dose increased the risk of an increase in sleep time by about 20% per night at night.
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Protection effect of morning preference
Cancer Research Rebecca Richmond, a researcher in the UK's Integrated Cancer Epidemiology Program, and the Integrative Epidemiology Unit (MRC) Integrative Epidemiology Unit at Bristol University acknowledged that the association may not be causal in the end. In nature.
She said in the press release: "The estimates we get are based on questions related to morning and evening preferences, whether people get up early or late in the day.
"Changing habits can be more complicated because the risk of breast cancer changes."
"However, our study of the protective effect of morning preference for breast cancer risk in our study is consistent with previous studies that emphasized the role of night shift and exposure to daylight as a risk factor for breast cancer. "
She believes that this result has potential policy implications that could affect the sleeping habits of the general population to improve health and reduce women's risk of breast cancer.
Dr. Cliona Clare Kirwan of the University of Manchester is a member of the NCRI Breast Clinical Study Group and has not been involved in this study.
She described the results as "interesting" and provided additional evidence of the effects of the body clock and sleep environment on breast cancer risk.
"Mendel's randomization in this study allows us to investigate the causal effects of various sleep patterns on breast cancer by observing variations in specific genes known to be associated with sleep characteristics," he added.
"This helps avoid misleading conclusions that can be influenced by disturbance factors."
Dr Emma Pennery, the clinical director of breast cancer treatment, has yet to question how the results can be applied to the real world.
"These interesting results emphasize the need for further investigation, but it is not as easy to change sleep habits as it is proven to be another proven risk reduction option, because they are often jobs, nursing or other health conditions," she said in a press release.
"For more research on how sleep characteristics can relate to cancer risk," says Pennery, "breast cancer is a very complex disease, and lifestyle changes do not guarantee breast cancer prevention.
"The biggest risk of becoming a woman and getting older is beyond our control, so every lifestyle change is related to identifying all the signs and symptoms of breast cancer."
Troubleshoot historical data discrepancies
Previous observational studies have confirmed the association between sleep patterns and breast cancer, but the results of night shift workers did not match.
The researchers investigated the relationship between sleep characteristics and breast cancer in 9599 breast cancer cases and 170616 controls in the British Biobank project.
To this end, they conducted a single-sample MR analysis on genotypic variants associated with chronotypes, insomnia and sleep duration to adjust the range of potential confounders.
The researchers focused on 351 genetic variations associated with chronotypes, 57 related to insomnia, and 91 maintained sleep.
The researchers performed MR analyzes of two samples based on a genome-wide association study of 122,977 breast cancer cases and 105,974 controls performed by the Breast Cancer Society Consortium (BCAC).
Richmond explains: "Mendel's method of randomization applied to this study is to identify causal risk factors for the disease because the genetic variation identified in relation to sleep characteristics is not affected by external or environmental factors So the onset of cancer can be used to determine the cause and effect relationship. "
Multivariate Cox regression analysis showed a weak correlation between sleep duration and insomnia symptoms at a risk prevalence of 0.95 (p = 0.002), which showed an inverse correlation between morning preference and breast cancer risk.
One-sample MR using British Biobank data strengthened the association between morning preference and reduced breast cancer risk and increased the risk ratio to 0.85 per category (p = 0.098).
Again, evidence for a link between breast cancer risk and sleep time or insomnia was weak.
The two-sample MR analysis of BCAC participants also supported association between morning preference and breast cancer risk, with an odds ration of 0.88 per category.
There was also evidence of a link between sleep time and breast cancer risk, which showed an increase of 1.19 per hour compared to the recommended 7-8 hours per night.
Evidence for a link between breast cancer risk and insomnia symptoms has been described as "contradictory" by researchers.
As a result of further calculations on the press release, the BCAC data showed that patients with morning cancer had a 40% lower risk of developing breast cancer than do evening types.
According to data from the UK Biobank, the risk of breast cancer was reduced by 48% when compared to the evening, if you preferred breakfast.
However, there was less relevance between breast cancer risk and insomnia or sleep duration in this population.
Next, the researchers plan to investigate a mechanism that explains the effects of different sleep characteristics on breast cancer risk.
Richmond explains, "We want to use genetic information from large populations to understand how the body's natural clock can contribute to breast cancer risk."
Dr Sowmiya Moorthie, a senior policy analyst at the Cambridge PHG Foundation, said the study is "solid" despite the lack of generalizability of non-European women. Of the used sample
She continued: "The implication of the study is that it supports existing evidence that sleep patterns affect cancer risk, but it does not explain how individual preferences for early or late rise interact with actual sleep behavior Is unclear.
"Whether an attempt to modify sleep behavior can help people manage their health and reduce cancer risk requires further investigation."
Dipender Gill, a clinical research training fellow at Imperial College London, said, "Despite the beneficial nature of the study, the study does not take any action other than additional investigations – people should not change sleep patterns according to evidence." Published here. "
"The statistical methods used in this study, called Mendel's randomization, do not always allow causal relationships to be inferred.
"In this case, the risks and risks associated with breast cancer can be a common cause."
Dr. Gil also pointed out that the pre-print edition had not yet undergone a peer-review.
Dr. Stephen Burgess, a postdoctoral fellow at the MRC Biostatistics Unit at Cambridge University, "made reservations" about the results and said, "It does not quite match up between the paper and the press."
"This is unfortunate because it means that the confidence interval for this value is not available."
"The key limitation is the lack of mechanisms," says Dr. Burgess. "The authors do not show the biological mechanism that sleep timing preference can influence breast cancer risk.
"Another limitation is that sleep timing preferences (chronotype) are self-reported and do not specifically employ people with sleep patterns, such as night shift workers.
The study was supported by Cancer Research UK, the Medical Research Council and the Economic and Social Research Council.
Samuel E. Jones is funded by the Medical Research Council. Timothy M. Frayling is supported by the European Research Council and Michael N. Weedon is supported by the Wellcome Trust.
2018 NCRI Cancer Conference. Abstract: Poster 1822. Released on November 6th.
bioRxiv 2018; 457572 doi: 10.1101 / 457572. abstract.