There are a few known risk factors associated with breast cancer, including alcohol consumption and obesity. Now, say researchers, we may need to add being a “night owl” to that list.
The new study, published this week in the BMJ, finds that women who considered themselves “morning people” were at a slightly lower risk (one less woman per 100) of developing breast cancer as opposed to whose who peak later in the day.
They also found a potential risk in those who tended to sleep longer than the recommended seven to eight hours, yet evidence tying breast cancer risk to insomnia was inconclusive.
These findings support previous studies that show a link between night shift employees and breast cancer, presumed to be caused by the disruption of the body’s circadian rhythm, lack of sunlight and other lifestyle choices.
Scientists collected health survey data from over 400,000 women — about 180,000 from the UK Biobank study and more than 220,000 from the Breast Cancer Association Consortium study — who self reported on their own sleep preferences.
However, peers in the field say this study should not be cause for worry or changing your sleep pattern.
“It is dangerous to suggest, even unintentionally, to women that changing their sleep patterns will significantly alter their risk of breast cancer,” Chris Bunce, professor of cancer biology at University of Birmingham, tells the Science Media Centre.
Bunce, who was not involved in the study, points out that the women who had a breast cancer diagnosis at the time of the survey may have experienced changes in sleep due to the cancer itself.
“In this case, self-reported sleep patterns and other non-genetic measures taken at time of study entry may not be the same as prior to developing cancer which is when the primary risk occurs,” he says.
Dr. John O’Neill of the Medical Research Council Laboratory of Molecular Biology in Cambridge, England, adds that a “less than one percent difference is a tiny effect size.”
“I would tend to make the opposite interpretation … that having an evening chronotype has very, very little bearing on the risk of breast cancer,” he adds. O’Neill was also not a part of this research.
While study authors cannot claim that changing your sleep schedule will reduce your odds of developing breast cancer, they do believe their results suggest that sleep has even more far-reaching effects that previously thought.
“The message is that perhaps people don’t fully appreciate that sleep is really important and does have health benefits beyond not feeling physically tired and being cognitively alert and so forth,” says study co-author Caroline Relton, professor of epigenetic epidemiology at the University of Bristol.
Still, she tells CNN, “The main lifestyle risk factors that we know are clearly associated with breast cancer are alcohol intake and obesity or high Body Mass Index.”