Getting too much sleep each night may affect cognitive function, especially in adults with depression, according to a study in Alzheimer’s & Dementia.
Vanessa M. Young, M.S., of the University of Texas Health Science Center at San Antonio, and colleagues examined data from 1,853 Framingham Heart Study participants ranging from 27 to 85 years old (mean age of 50) who did not have dementia or stroke. They asked the participants about antidepressant use and assessed the participants for depression. They then divided the participants into four groups:
- No depressive symptoms, not taking antidepressants
- Depressive symptoms, not taking antidepressants
- No depressive symptoms, taking antidepressants
- Depressive symptoms, taking antidepressants
In each group, participants self-reported the number of hours they slept per night and were categorized as having short sleep (six hours or less), average sleep (between six and nine hours), and long sleep (nine hours or more). They also took a battery of tests to assess their cognitive performance.
Overall, compared with participants with average sleep, those with long sleep had poorer performance in global cognition, executive function, visuospatial memory, and verbal learning/memory tasks.
“These findings suggest that sleeping ≥ 9 hours per night is associated with cognitive differences equivalent to 6.5 years of brain aging,” Young and colleagues wrote.
Among individual patient groups, the strongest negative associations between long sleep and cognition were among individuals with depressive symptoms, regardless of antidepressant usage. There was a smaller effect of long sleep among adults with no depression and no antidepressant use, while no cognitive effect of long sleep was seen in adults who took antidepressants but had no depressive symptoms.
Young and colleagues suggested that antidepressant use among those with no depressive symptoms may reduce nighttime awakenings, improve restorative sleep, or stabilize sleep–wake timing. “However, whether this observation reflects antidepressant treatment, symptom remission, or other unmeasured aspects of sleep health remains unclear, given the limitations of our sleep measures.”
The researchers also did not find a statistically significant relationship between short sleep and cognitive performance.
“These results diverge from some studies that have identified short sleep as a risk factor for cognitive impairment,” they wrote. “The precision of this association may increase with greater statistical power or in older populations in which short sleep and cognitive impairment may be more prevalent.”
For related information, see the Psychiatric News article “Poor Quality Sleep in Midlife Linked to Poor Cognition 11 Years Later.”
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