Primary investigator Meredith Rowe of the University of Florida said the researchers had expected the caregivers' main sleep problem would be more time awake in the middle of the night when the person with dementia needed supervision. However, both caregivers and non-caregivers had an average of more than 40 minutes of time awake during the night after initially falling asleep.

"On average, caregivers only slept about six -and-a-half hours a night and took almost 23 minutes to fall asleep," Rowe said in a statement. "Using the sleep diary data that subjects kept at the same time, however, depression was the primary determinant of poor sleep with depressed subjects reporting less time asleep and more wake time over the week."

When sleep was measured objectively and adjustments made for depression, age, health condition and education, the 31 caregivers studied had 33 minutes less total sleep than the 102 non-caregivers with whom they were compared. Both groups were older, mostly female, relatively healthy, white and currently married adults. The non-caregiver sample had a significantly greater level of education than the caregiver sample.

The findings were published in the Journal of Clinical Sleep Medicine.