New Study: Waking up Early, Helps Lower Risk Of Breast Cancer
Women who are naturally early risers were found to have lower risk of developing breast cancer than evening types in a new study. One in 100 women who considered themselves morning people developed breast cancer, compared with two in every 100 women who called themselves evening people.
Cancer risks associated with a person's body clock and sleep patterns have been reported in previous research and the UK researchers wanted to explore sleep traits in more detail, as well as any genetic factors underlying this.
Self-reported preferences for mornings or evenings (by their own definition of that preference) were recorded in more than 180,000 women, led by Dr. Rebecca Richmond, research fellow in the Cancer Research UK Integrative Cancer Epidemiology Program and the Epidemiology Unit at the University of Bristol, and presented Tuesday at the NCRI Cancer Conference in Glasgow.
Richmond's team also analyzed genetic variants linked to whether someone is a morning or night person in more than 220,000 women to find out if these could help provide a causal link to breast cancer.
This type of statistical model, called Mendelian randomization, showed that people whose genes made them more likely to be early risers were less likely to develop breast cancer by as much as 48%, as shown from the 220,000 participants in the study.
The second analysis, using self-reported data on sleep from 180,000 participants, showed a similar trend of early rising women having a 40% lower risk of breast cancer. The variation is due to technical differences, stated Richmond.
Women who self-reported sleeping more than the average seven to eight hours per night were also found to have a slightly increased risk of breast cancer, of 20% per extra hour slept, according to the team's Mendelian randomization analysis.
But the team point out that many factors are involved in a person developing breast cancer and that these numbers are not an absolute risk. Also, the findings cannot be applied across populations as the majority of women included were of European ancestry.
Not as large as other factors
Richmond stressed that the 48% lower risk was identified among "extreme" cases, where people identified themselves as "definite" morning people out of the five categories they could chose from -- definite morning, more morning than evening, neither, more evening than morning, definite evening.
"Sleep is likely to be an important risk factor for breast cancer," she said. But it isn't as large a risk factor as other well established ones, such as weight or alcohol consumption, added Richmond.
Night owls shouldn't be worried by the findings, said Richmond. "I wouldn't support that women should get up earlier to reduce risk of breast cancer."
There are theories around the causes of sleep's effect on cancer, she said, such as the idea that artificial light at night leads to hormonal disruption.
Dr. Sowmiya Moorthie, senior policy analyst in epidemiology at PHG Foundation, who was not involved in the research, added that the study's major strength is the use of "multiple approaches to examine the links between sleep traits and breast cancer, which allows the researchers to demonstrate consistency in their findings."
"In terms of the implications of the research, it supports existing evidence that sleep patterns influence cancer risk, but it remains unclear how individual preferences for early or late rising interact with actual sleep behaviours," Moorthie wrote in an email.