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A new study found that women who were naturally in early pregnancy had a lower risk of breast cancer than women in the evening. Breast cancer is the cause of one in 100 women who consider themselves as morning people, against two out of 100 women who call themselves at night.
Cancer risks associated with a person's body clock and sleeping habits had already been reported, and British researchers wanted to explore in more detail sleep characteristics and the underlying genetic factors.
Self-declared preferences for mornings or evenings (according to their own definition of this preference) have been recorded led by Dr. Rebecca Richmond, a researcher in the Integrative Cancer Epidemiology Program at Cancer Research UK and the Epidemiology Unit at the University of Bristol, and presented Tuesday at the NCRI cancer conference in Glasgow.
The Richmond team also analyzed the genetic variants related to whether it is a morning or evening person. more than 220,000 women have asked if they could help establish a causal relationship to breast cancer.
This type of statistical model, called Mendelian randomization, showed that people whose genes made them more likely to get up early were less likely to develop breast cancer. up to 48%, as shown by the 220,000 participants in the study.
The second analysis, using self-reported sleep data from 180,000 participants, showed a similar pattern in early-stage women with a 40% reduction in breast cancer risk. The variation is due to technical differences, said Richmond.
According to the team's Mendelian randomization analysis, women who reported sleeping more than seven to eight hours per night on average also had a slightly higher risk of breast cancer, an additional 20% per hour of sleep.
However, the team pointed out that the development of breast cancer was linked to many factors and that these figures did not represent an absolute risk. In addition, the results can not be applied to all populations because the majority of women included were of European origin.
"Sleep is probably a major risk factor for breast cancer, but it is not as important as other well-established risk factors such as BMI or alcohol," said Richmond.
The American Cancer Society said that 45% of cancer deaths in the United States are related to modifiable risk factors, such as cigarette smoke, excess weight, red meat consumption and transformed and physical inactivity. In the United States, about 4% of cancer deaths were related to alcohol consumption and the charity Breast Cancer Now warns that any alcohol consumption increases the risk of breast cancer. And obesity is fast becoming the leading preventable cause of breast cancer among women in the UK, according to a report released earlier this year.
"We know that sleep is generally important for health," said Richmond. "These results have potential policy implications for influencing sleep patterns of the general population to improve health and reduce the risk of breast cancer in women."
Our circadian rhythms, or body clocks, control body functions such as sleep patterns, blood pressure and metabolism. When disturbed, they can increase the risk of cancer and other diseases.
The Richmond team conducted their genetic analysis in hopes of better understanding the possible causes and consequences of this link. However, experts caution that more research is needed and that existing results can not be applied more widely.
"The statistical method used in this study, called Mendelian randomization, does not always infer causality," said Dipender Gill, a research fellow in clinical research training at Imperial College London. "For example, genetic determinants of sleep can also affect other neuronal mechanisms that affect the risk of breast cancer regardless of sleep patterns. In such a scenario, sleep patterns may be associated with the risk of breast cancer, but not directly to the origin of the cancer. "
Stephen Burgess, a postdoctoral fellow at the University of Cambridge, added that a mechanism to explain the link was also neither known nor understood.
"The authors do not show any biological mechanism by which the preference for sleep time choice could affect the risk of breast cancer. Another limitation is that the sleep timing preference (chronotype) is self-reported, and the survey did not specifically recruit individuals with different sleep patterns, such as night workers, "Burgess wrote. in the comments of the study.
The study has not yet been published in a medical journal. Gill added that he had not yet been reviewed by experts in the field.
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Not as big as any other factors
Richmond pointed out that the lower risk of 48% was identified among the "extreme" cases, in which people identified themselves as "definitive" in the morning among the five categories from which they could choose – definite in the morning, plus in the morning only in the evening, no more in the evening than in the morning, final evening.
"Sleep is likely to be a significant risk factor for breast cancer," she said. But it's not as important a risk factor as other well-established factors, such as weight or alcohol consumption, added Richmond.
Night owls should not worry about the results, said Richmond. "I would not argue that women should get up early to reduce the risk of breast cancer."
According to her, there are theories about the causes of the effect of sleep on cancer, including the idea that artificial night light causes hormonal disorders.
Dr. Sowmiya Moorthie, senior policy epidemiologist at the PHG Foundation, who did not participate in the research, added that the major strength of the study lies in the use of "multiple approaches to examining linkages". between sleep characteristics and breast cancer, allowing researchers to be consistent in their conclusions. "
"Regarding the implications of the research, it corroborates the existing evidence that sleep patterns affect cancer risk, but it is still unclear how individual preferences for getting up sooner or later interact with cancer behaviors. real sleep, "wrote Moorthie in an email.
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