Sleeping too little is harmful, as we all know, but getting too many hours of sleep might not be the best choice, either. This suggestion comes from a large-scale study published in the journal Nature, conducted by researchers from Columbia University (USA) in partnership with other international institutions. It analysed the data of over half a million people, and was able to identify an actual “ideal range” of sleep duration associated with slower biological ageing and a lower risk of chronic disease.
According to the researchers, this balance can be found somewhere between six and a half and eight hours of sleep per night. Naturally, this number will not apply to everyone. However, in the population studied, this range was associated with better health indicators throughout the body.
To arrive at this conclusion, the researchers had to analyse subjects’ biological ageing clocks – which measure the rates at which organs and tissues are ageing – and then assess them in relation to the subjects’ sleep habits.
The study, conducted by the MULTI Consortium, used data from the UK Biobank, one of the largest biomedical data banks in the world, and involved over 500,000 adults between the ages of 37 and 84. The authors developed a tool called the Sleep Chart, with the goal of assessing the relationship between sleep duration and 23 different biological ageing clocks, data acquired through magnetic resonance image-guided proteomics (the study of the proteins in the body) and metabolomics (the analysis of metabolites, the small molecules produced by metabolic processes).
The analysis brought to light a U-shaped pattern. The best biological ageing rates were found among those who slept between 6.4 and 7.8 hours, while both those who slept less than 6 hours and those who slept more than 8 showed signs of faster ageing. This association held true across numerous organs and systems, including the brain, the cardiovascular system, liver, metabolism, and immune system. In fact, the researchers found that insufficient and excessive sleep duration were both linked to an increased risk of developing a range of conditions, including depression, diabetes, and other systemic diseases, as well as increased all-cause mortality during the period of the study.
Thanks to the huge number of participants and the use of sophisticated biomarkers, the study's results are certainly sound. Its authors urge caution nonetheless. The study shows an association, not a definite cause-and-effect relationship.
Sleeping for many hours could, for example, be the consequence of pre-existing health conditions and not necessarily the direct cause of faster ageing. Not even genetic testing carried out by the researchers could rule out this possibility entirely. What's more, sleep duration data was self-reported via questionnaires filled out by the participants and not collected using objective tools like polysomnography.
Regardless, the results of the study appear to be in line with the recommendations of leading scientific organisations, such as the American Academy of Sleep Medicine and the Sleep Research Society, according to whom adults should sleep for at least 7 hours per night to maintain good health. However, sleep needs may vary based on age, genetics, lifestyle, and any illnesses an individual might have. Therefore, rather than strive for a precise number of hours, experts advise aiming for a regular sleep pattern:
This study reinforces a message that continues to be bolstered by research: sleep is not time wasted, but rather it is a cornerstone of good health. Paying attention to the quality of your rest and the regularity of your habits can make all the difference, and is much less complicated than counting hours.