Being a morning person may reduce your risk of breast cancer, research suggests.A study found those who prefer to get up bright and early are less likely to develop the disease than ‘night owls’.This is believed to be due to light exposure in the early hours cutting off the supply of the hormone melatonin, which regulates sleep.Several studies have shown melatonin has the power to protect against cancers, particularly breast.
The new research found for every 100 women, one less will develop the disease if she gets up, and goes to bed, early.The results also found the participants who slept for more than seven-to-eight hours were more likely to get breast cancer.
Critics have pointed out this is a ‘tiny effect’, saying when our bedtime is has a ‘very, very little bearing on our risk of breast cancer’. Working late shifts have repeatedly been linked to the disease in recent years, the researchers wrote in the British Medical Journal.
This is thought to be due to how the shift disrupts our body clock and exposes us to light at night. The World Health Organization even classified shift work that disrupts the body clock as being ‘probably carcinogenic to humans’ in 2007.However, less is known about how insomnia, disturbed sleep and being a ‘morning or evening person’ affects our health. University of Bristol experts, led by Professor Caroline Relton, investigated whether shut eye impacts breast cancer risk.
They looked for genetic ‘traits’ that are ‘robustly associated’ with insomnia, sleep duration and our preference for mornings or evenings. These traits were screened for in 180,216 women who took part in the United Kingdom (UK) Biobank study, and 228,951 women with breast cancer.All the participants also completed a questionnaire about their sleep habits. Results revealed the women who reported preferring mornings to evenings were slightly less likely to develop breast cancer. The researchers wrote their findings ‘provide strong evidence for a causal effect of chronotype on breast cancer risk’.
Chronotype refers to the ‘time’ our body clock ‘prefers’, with some people being morning larks and others night owls. Dr. John O’Neill, research group leader at the Medical Research Council’s Laboratory of Molecular Biology, said: ‘A less than one per cent difference is a tiny effect size.
Explained: how the circadian rhythm works
In a healthy person, cortisol levels peak at around 8am, which wakes us up (in theory), and drop to their lowest at 3am the next day, before rising back to its peak five hours later. Ideally, this 8am peak will be triggered by exposure to sunlight, if not an alarm. When it does, the adrenal glands and brain will start pumping adrenalin.
By mid-morning, the cortisol levels start dropping, while the adrenalin (for energy) and serotonin (a mood stabilizer) keep pumping. At midday, metabolism and core body temperature ramp up, getting us hungry and ready to eat. After noon, cortisol levels start their steady decline. Metabolism slows down and tiredness sets in. Gradually the serotonin turns into melatonin, which induces sleepiness. Our blood sugar levels decrease, and at 3am, when we are in the middle of our sleep, cortisol levels hit a 24-hour low.
“I would tend to make the opposite interpretation to their press release, that having an evening chronotype has very, very little bearing on the risk of breast cancer.”Dr. O’Neill also pointed out the findings just show a correlation and do not prove that our bedtime drives our cancer risk.Dr. Chris Bunce, professor of translational cancer biology at the University of Birmingham, agreed. “The associations observed are very small correlative,” he said. “It is dangerous to suggest, even unintentionally, to women that changing their sleep patterns will significantly alter their risk of breast cancer.”
Professor Relton and colleagues were unable to explain why the risk was higher in women who slept for longer each night. And the researchers stress their study relied on the participants self-reporting their sleep habits. The women were also all of European ancestry and therefore different results may apply to other ethnicities, they add. More research is also required to uncover exactly how different sleep patterns may lead to breast cancer. Despite the critics’ reservations, the researchers said the findings ‘have potential implications for influencing [the] sleep habits of the general population in order to improve health’.