You snooze, you lose: oversleeping and cardiac health
Research published in the European Heart Journal has found the old adage “all good things in moderation” extends to how much we sleep.
The study involved data from more than 116,000 people from seven regions across the world and found that people who slept for longer than the recommended six to eight hours a day, including daytime naps, had an increased risk of dying or developing diseases of the heart or blood vessels in the brain.
A team of five cardiology experts, including Associate Professor Dominik Linz, Professor Prash Sanders and Dr Kadhim Kadhim from the SAHMRI-based Centre for Heart Rhythm Disorders, co-authored an editorial that accompanied the publication in the European Heart Journal.
In it, they cautioned that daytime napping or “excess” sleep could be a symptom of underlying cardiovascular issues rather than a cause.
“Daytime naps could represent a physiological response to disease-related disturbed sleep, even in those with normal sleep durations,” the editorial states.
“This can potentially indicate that subclinical non-diagnosed cardiovascular disease may explain some of the association between daytime napping and major cardiovascular events in patients with sufficient sleep duration during the night.”
The original research was led by Chuangshi Wang, a PhD student at McMaster and Peking Union Medical College, Chinese Academy of Medical Sciences, China, working at the Population Health Research Institute at McMaster. It found that, compared to people who slept for the recommended time, those who slept a total of eight to nine hours a day had a 5% increased risk; people sleeping between nine and ten hours a day had an increased risk of 17% and those sleeping more than ten hours a day had a 41% increased risk.
During a median follow-up time of nearly eight years, 4381 people died and 4365 suffered a major cardiovascular problem such as a heart attack or stroke. The researchers adjusted the results to take account of factors that could affect outcomes, such as age, sex, education, smoking, alcohol consumption, whether the participants lived in urban or rural areas, had a family history of cardiovascular disease, or had a history of diabetes, raised blood pressure, chronic obstructive pulmonary disease or depression.
Associations between sleep and death or cardiovascular and other diseases have been suggested by other studies, but results have been contradictory. In addition, they tended to look at particular populations and did not necessarily take account of the fact that in some countries daytime napping can be common and considered healthy.
The researchers found regular daytime naps were more common in the Middle East, China, Southeast Asia and South America. The duration of daytime naps varied mainly from 30 to 60 minutes. People who slept six or fewer hours at night, but took a daytime nap, and so slept an average of 6.4 hours a day in total, had a slightly increased risk compared to those who slept between six and eight hours at night without a daytime nap, but this finding was not statistically significant.
“Although daytime napping was associated with higher risks of death or cardiovascular problems in those with sufficient or longer sleep at night, this was not the case in people who slept under six hours at night. In these individuals, a daytime nap seemed to compensate for the lack of sleep at night and to mitigate the risks,” Ms Wang added.
Associate Professor Linz says the research should prompt doctors and patients to be more conscious of sleep patterns, particularly for those at risk of cardiovascular problems.
“We need to be aware and communicate to our patients, that sleeping a lot and having daytime naps may not always be harmless,” he said.
“Perhaps the ancient Greek poet Homer, author of the Iliad and the Odyssey, summed it up millennia ago when he said: ‘Even where sleep is concerned, too much is a bad thing’.”
The European Heart Journal study looked at a total of 116,632 adults aged between 35 and 70 years in 21 countries with different income levels in seven geographic regions (North America and Europe, South America, the Middle East, South Asia, Southeast Asia, China and Africa). They were part of the Prospective Urban Rural Epidemiology (PURE) study that started in 2003.
Limitations of the study include that the researchers estimated nocturnal sleep time based on the space between going to bed and waking up, and that they assumed that the duration of night time and daytime naps remained unchanged during the follow-up period. Nor did they collect information on sleep disorders such as insomnia and apnoea, which can have an impact on sleep and might also affect health.