We spend most of our life sleeping and sleep is an important phase of our day, because it allows us to recover physical and mental energies. Different studies have tried to identify what the ideal duration of sleep is and a few years ago the National Sleep Foundation issued some specific recommendations for different age groups.
The panel agreed that, for healthy individuals, the appropriate sleep duration for adolescents is between 8 and 10 hours, for young adults and adults between 7 and 9 hours, and for seniors between 7 and 8 hours.
What happens if these references are not respected? Also in this case, the published studies are many and almost always emerges clearly that out of these sleep duration intervals different health problems emerge.
Thus, a short sleep has been associated with an increased risk of obesity, diabetes mellitus, cardiovascular disease, and even all-cause mortality. However, an increased risk for these diseases was also highlighted in people who sleep too long. Therefore, it seems that, in order to stay healthy, one must sleep for a specific number of hours each night, without reductions or excesses.
Increased deposits of amyloid β substance
One of the fields in which research in this area has been most developed is that which has evaluated the correlations between hours of sleep and alterations in higher brain functions.
A recent study, published in the journal JAMA Neurology, showed that both short and long sleep duration are associated with an increased risk of developing cognitive decline. Research also shows that reduced and excess sleep hours can also cause greater deposits of amyloid β, a substance characteristic of Alzheimer’s disease, greater depressive symptoms, and a higher body mass index in the elderly.
This research used data collected in the Anti-Amyloid Treatment in Asymptomatic Alzheimer’s Disease study, conducted in the United States, Canada, Australia, and Japan. The subjects included in the analysis were aged between 65 and 85 years, had complete data on the apolipoprotein E genotype, were not suffering from dementia and had an intact cognitive profile. All had undergone a positron emission tomography (PET) scan for amyloid β.
The aim of the study was to evaluate the associations between sleep duration, as reported by the patient, and cerebral amyloid β load, as well as demographic, cognitive and lifestyle variables in adults with normal cognition.
The duration of sleep was categorized into three categories: short, 6 hours; normal, 7-8 hours; long, 9 hours.
A reduced cognitive performance
The results of the analysis showed that a short sleep duration was linearly associated with a higher load of amyloid β; it was also associated with reduced cognitive performance, mainly in the memory domains.
In contrast, no difference in amyloid β concentration was found between the long and normal sleep duration groups. On the other hand, those who slept longer or too few hours had a higher body mass index and depressive symptoms, compared to those who slept a number of hours considered normal. Finally, long sleep duration was associated with poorer performance in multiple cognitive domains.
Neither too much nor too little
Therefore, this new study also seems to confirm that in medio stat virtus. Adults need to get 7-8 hours of sleep a night, otherwise they risk major health problems.
In particular, the dangerous association between the short sleep and the accumulation of amyloid β is highlighted. Fortunately, this was not present also in those with long sleep.
The accumulation of this substance has been attributed to the fact that it is mainly produced during wake and is removed during sleep, in the REM phases, when dreaming. An accumulation that in aging is associated with the onset of Alzheimer’s disease.
On the other hand, the excessive duration of sleep still seems to cause a worsening of cognitive functions with aging, which therefore seem independent of the deposition of amyloid β.
All these results, substantially in line with other research published in this area, therefore seem to confirm the importance of sleeping an adequate, but not excessive, number of hours.
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