There is nothing better than a good night's sleep. It helps us relax, recover and is linked to better mental health and lower heart disease and diabetes risk.
But, there is a fine line, as too little or too much could be bad. So what's correct?
Researchers from the Washington University School of Medicine have published a recent study that sleeping too much may be linked with cognitive decline.
The research looked at 100 older adults in their mid-to-late 70s on average, tracking them between four and five years.
When the study began, 88 people did not show any signs of dementia, while 12 showed signs of cognitive impairment.
Senior Lecturer in Psychology & Associate Director Greg Elder wrote on The Conversation, "Throughout the study, participants were asked to complete a range of commonplace cognitive and neuropsychological tests to look for signs of cognitive decline or dementia. Their scores from these tests were then combined into a single score, called the Preclinical Alzheimer Cognitive Composite (PACC) score. The higher the score, the better their cognition was over time."
"Sleep was measured using a single-electrode encephalography (EEG) device, which participants wore on their forehead while sleeping, for a total of between four to six nights. This was done once, three years after people first completed their annual cognitive tests. This EEG allowed the researchers to accurately measure brain activity, which would tell them whether or not someone was asleep (and for how long), and how restful that sleep was."
"Although sleep was only measured at one period during the study, this still gave the research team a good indication of participants' normal sleep habits. While using an EEG to measure brain activity may be somewhat disruptive to sleep on the first night, as people get used to the equipment, sleep tends to return to normal the following night. This means that when sleep is tracked from the second night onwards, it's a good representation of a person's normal sleep habits."
So, what's this all mean? Sleeping less than 4.5 hours and more than 6.5 hours a night, with a poor quality sleep, was associated with cognitive decline over time.