Older adults whose sleep duration varied over the course of a two-decade-long study were much more likely to develop cognitive decline compared with those whose sleep duration did not vary significantly, new research shows.

“Our finding tells us that maintaining healthy, consistent sleep habits long-term may be important in optimizing brain health as you age. So making sure that good sleep is a regular part of your life —not just on weekends, and not just on vacations — is important,” said Dr. Jeffrey Iliff, a professor of psychiatry and behavioral sciences and neurology at the University of Washington School of Medicine.

Iliff, who also conducts research at the VA Puget Sound Health Care System, led the investigation. Samantha Keil, formerly of UW and now a senior research fellow at Weill Cornell Medicine, was the paper’s lead author. They and colleagues report their findings today in the journal JAMA Network Open.

Previous research has suggested that sleep of short duration, less than six hours a night, increases the risk of cognitive decline. The new study also found this to be true. But the finding that variation of sleep duration appeared to affect cognitive decline is new.