Consistently going to bed and waking up at different times may affect our circadian rhythm, throwing our body鈥檚 various physiological processes out of sync and increasing the risk of dying in a given length of time. However, pre-existing medical conditions can also affect sleep. These inconsistent sleep habits may therefore correlate with, rather than cause, an increased risk of death over a given period.
at Monash University in Melbourne, Australia, and his colleagues studied the sleeping habits of 88,975 people aged between 40 and 69, using information recorded in the UK Biobank database.
From this information, they created a so-called sleep regularity index (SRI) that reflected the likelihood that the participants would be asleep or awake at a particular time each day. Someone who goes to sleep and wakes up at exactly the same time every day would have an SRI of 100, whereas doing so at completely different times would give a score of 0, says Pase.
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After calculating each of the participants鈥� SRIs across one week, the researchers followed up with them for seven years. Compared with the participants with the average SRI of 61, those who scored 41 or below were 53 per cent more likely to die from any cause over the seven-year follow-up. They were also 88 per cent more likely to die from heart disease and 36 per cent more likely to die from cancer specifically.
These figures describe their relative risk of dying over the follow-up period, which compares the risk among the participants with an SRI of 41 or below relative to the risk of those with an SRI of 61. This is different from an absolute risk, which takes into account the risk we all have of dying over a 7-year period.
Pase says the results may be due to circadian misalignment, disruption to the body鈥檚 approximately 24-hour cycles that influence our physiology and behaviour. , as our body clocks are critical to cell division and alterations may trigger abnormal cell proliferation, he says.
at the University of Oxford says the heightened risk of heart disease wasn鈥檛 unexpected. No one would be surprised if a study demonstrated that a lack of water, food or oxygen negatively affects our cardiovascular health, he says. 鈥淚 think [sleep] belongs in that set of things.鈥�
However, many of the participants had already been diagnosed with a potentially life-threatening health condition at the start of the study. For example, 41 per cent had a heart condition and 13 per cent had cancer. These can disrupt sleep, either by causing physiological changes within the body or due to the anxiety of living with the condition, says Pase.
The study鈥檚 method could have also led to inaccuracies in the results. The participants鈥� sleep information was collected via a wrist-worn sensor called an accelerometer, which measured their movement. If a participant was still for several hours at a time, the researchers assumed they were asleep.
An alternative way of gauging if someone is asleep is via polysomnography, which records their brain waves, blood oxygen levels, heart rate and breathing. This would have been a more accurate approach, but an accelerometer can be worn at home, avoiding the need for participants to stay in a clinic, says Pase.
Sleep diary information would also have helped to back up the findings of the accelerometer, but this wasn鈥檛 included in the database, he says.
The researchers have since looked into whether sleep irregularity is linked to dementia, with a paper expected later this year.
medRxiv
