In aging women, difficulty sleeping may be a marker for cognitive decline, a cause of it, or both. In a 15-year study, 2,400 women (age 65 or older) were followed for cognitive decline. The women who demonstrated a decline in cognitive ability were much more likely to suffer from sleep difficulties from poor sleep efficiency, longer sleep latency, and more fragmented sleep.

Although early pathologic changes could account for both difficulty in sleeping and cognitive decline, the researchers speculate that a decrease in cognitive abilities could also be connected to anxiety or depression, or other neuropsychiatric disturbances.

Source