Sleeping too much may seem harmless, or even beneficial. However, researchers warn: beyond a certain threshold, sleep ceases to be restorative and could even weaken the brain. Excessive duration would thus be linked to a decline in cognitive functions and mood disorders.
Sleeping too much: the brain loses efficiency
Sleep is a necessity, but too much sleep can backfire. A study conducted by the University of Texas on 1,853 adults in the Framingham Heart Study cohort reveals that beyond nine hours of sleep per night, cognitive abilities begin to decline. The participants, aged on average 50 years, were divided into three profiles: short sleepers (less than 6 hours), average sleepers (6 to 9 hours) and heavy sleepers (more than 9 hours).
“Long sleep was associated with decreased overall cognitive abilities, including memory, executive functions, and visuospatial skills“, says Dr. Sudha Seshadri, behavioral neurologist and distinguished professor of neurology, psychiatry and cellular physiology.
Why going beyond nine o’clock can become dangerous
Researchers also found that this decline in brain performance was accentuated in people suffering from depression. “These associations were stronger in people with depressive symptoms, regardless of antidepressant use“, adds the scientist. “Sleep could therefore constitute a modifiable risk factor for cognitive decline in people suffering from depression“.
An observation shared by Dr Jonathan Taieb, sleep doctor in Paris: “For children and adolescents, sleeping more than 9 hours a night is completely normal. But among those over 65, sleeping 8 to 9 hours becomes excessive.“Excess sleep can reveal an underlying disorder,” he says.This may be linked to depression, sleep apnea, hypothyroidism, an inflammatory disease or even idiopathic hypersomnia.“.
When should you consult?
While some people naturally sleep longer, this is not always a cause for concern. “Around 10% of the population has a physiological need to sleep longer. These are the ‘heavy sleepers’“, specifies Dr Taieb. On the other hand, an excessive need for long-term sleep should raise alarms.”Sleeping more a few days after a period of overwork should not worry“, he reassures, before qualifying: “But if it lasts more than a week, with attention problems, daytime sleepiness or an alteration in quality of life, it is better to consult“.