Risks associated with body and sleep patterns were noted in previous research, and British scientists wanted to examine in more detail the characteristics of sleep, as well as all the genetic factors on which it is based.
Preferences for wounds or evenings were recorded in more than 180,000 women led by Dr. Rebecca Richmond, a researcher in the Cancer Research UK Integrative Cancer Epidemiology Program and the Epidemiology Unit at Bristol University and presented Tuesday at the NCRI Cancer Conference in Glasgow.
Richmond's team also analyzed genetic variants associated with whether someone is a morning or a night person in more than 220,000 women to see if it could help ensure a causal link with breast cancer.
This type of statistical model, called Mendelian randomization, has shown that people whose genes cause them to be more likely to be earlier rising are less likely to develop breast cancer up to 48%, as shown by 220,000 study participants.
A second analysis, using its own reported sleep data from 180,000 participants, showed a similar trend in early-stage women with a 40% lower risk of breast cancer. The difference is due to technical differences, Richmond said.
Women who thought they were sleeping more than average seven to eight o'clock in the night also found a moderate increase in breast cancer risk by 20% per hour of sleep according to Mendel's randomization analysis.
But this points to the fact that a number of factors are involved in a person who develops breast cancer and that these numbers are not an absolute risk. Conclusions can not be used across the population, as most women included European ancestors.
"Sleep is probably an important risk factor for breast cancer, but it's not as big as other well-established risk factors like BMI or alcohol," Richmond said.
"We know that sleep is generally important for health," Richmond said. "These findings have potential policy implications for influencing the sleep habits of the common population in order 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, and when they are disturbed, they can increase the risk of developing cancer and other illnesses.
Richmond's team carried out their genetic analysis in hopes of kicking out the possible causes and consequences of this link. Experts warn that further research is needed and existing findings can not be used in a broader spectrum.
"The statistical method used in this study called Mendel's randomization does not always allow for causality," said Dipender Gill, a clinical researcher at Imperial College, London. "For example, genetic determinants of sleep may also affect other neuronal mechanisms that affect the risk of breast cancer independently of sleep patterns, in which case sleep patterns may be associated with a risk of breast cancer but not directly cause it."
Stephen Burgess, a postgraduate student at Cambridge University, added that the mechanism that explains the link is not known or understood.
"The authors do not show any biological mechanism that could influence the risk of breast cancer on the basis of sleep timing. Another limitation is that premature sleep timing (chronotype) is reported on its own, and investigations do not specifically recover individuals with different sleep patterns, night workers , "wrote Burgess in the study's comments.
The study must still be published in the medical journal. Gill added that he has not been explored yet by other industry experts.
Not as big as other factors
Richmond stressed that a 48% lower risk was found between "extreme" cases where people identified themselves as "definitive" morning people from the five categories they chose – the final morning, more in the morning than in the evening, the morning, some evening.
"Sleep is probably an important risk factor for breast cancer," she said. But it's not as much a risk factor as other well-established ones, such as alcohol or weight, Richmond added.
Night owls should not worry about finding, Richmond said. "I would not encourage women to get up early to reduce the risk of breast cancer."
There are theories about the causes of sleep's impact on cancer, as he says, such as the idea that artificial light at night leads to hormonal disturbance.
Dr. Sowmiya Moorthie, a senior policy analyst for epidemiology at the PHG Foundation, said she was "using multiple approaches to investigating the links between sleep patterns and breast cancer, enabling scientists to demonstrate the consistency of their findings."
"With regard to the implications of research, it supports existing evidence that sleep patterns affect the risk of cancer, but it remains unclear how individual preferences for early or late rises affect the actual behavior of sleep," Moorthie wrote in an e-mail.