A study published in the journalBrainhas found that 7.5 hours is the exact amount needed to promote overall better brain health and offset Alzheimer's disease.
How was the study conducted?
The research consisted in analysing 100 elderly adults (the average age being 75) using tiny monitors strapped to their foreheads to measure brain activity during sleep.
The study lasted four and a half years, which also saw scientists sampling the cerebrospinal fluid of participants. This liquid is found within the tissue that surrounds the brain and spinal cord and can be used to measure a person's levels of Alzheimer's proteins.
Ultimately, cognitive scores saw a significant decline in groups of people who slept less than five and a half and slept more than seven and a half hours per night.
Previous findings on the topic of the ideal number of hours one should be sleeping each day linked memory loss, confusion and being slower to learn new things—symptoms of Alzheimer's—to poor quality and quantity of sleep. Associate professor of neurology at Washington University Sleep Medicine Centre Dr Brendan Lucey explained that:
Our study suggests that there is a middle range, or 'sweet spot', for total sleep time where cognitive performance was stable over time. Short and long sleep times were associated with worse cognitive performance, perhaps due to insufficient sleep or poor sleep quality.
How many hours should the average person be sleeping?
Though this specific study looked into the hours of sleep needed to prevent Alzheimer's, the average hours for adults between the ages of 26 and 64 is anywhere between seven and nine.
According to Max Hirshkowitz, sleep physician at Harvard and president of the National Sleep Foundation, the most important thing to consider is to feel good and refreshed when you wake up. That means that if you are not hitting the target amount recommended, this might just mean that your body functions slightly different than the average.