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’.
Being a morning person could reduce your risk of breast cancer, research suggests (stock)
One in eight women in the UK and US will develop breast cancer at some point in their lives, statistics show.
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 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.
‘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’.
Professor Eva Schernhammer, chair of the department of epidemiology at the University of Vienna, said the results ‘identify a need for future research, exploring how the stresses on our biological clock can be reduced’.
In a linked editorial, she added the study could help women look after their health into old age and avoid diseases that are related to a ‘disturbed’ body clock.
‘People with the greatest mismatch between internal physiological timing and external societal demands are at risk of circadian misalignment,’ she wrote.
‘Night shift work is one of the gravest external stresses on the circadian clock.
‘[It] necessitates profound changes to the timing of behaviours such as eating and sleeping, resulting in circadian disruption or misalignment.
‘Night work alters the circadian clock’s primary output—melatonin rhythms—most seriously when working hours are mismatched with preferred sleep timing: Morning people working night shifts, or evening people working morning shifts.
‘Chronic exposure to circadian disruption adversely affects long-term health, increasing the risk of death from major causes, including cancer, particularly breast’.