However, researchers also pointed out that this can be improved through simple, low-cost interventions.
Researchers in the study published in the journal 'JAMA' analysed 35 studies with data from 3,268 caregivers.
Informal caregiving for a person with dementia is akin to adding a part-time but unpaid job to one's life, with family members averaging 21.9 hours of caregiving, according to The Alzheimer's Association estimates.
"Losing 3.5 hours of sleep per week does not seem much, but caregivers often experience accumulation of sleep loss over years," said lead author Chenlu Gao, a doctoral candidate of psychology and neuroscience in Baylor's College of Arts and Sciences.
"It can have a strong impact on caregivers' cognition and mental and physical health. But improving caregivers' sleep quality through low-cost behavioural interventions can significantly improve their functions and quality of life," said Gao.
Chronic stress is associated with short sleep and poor-quality sleep. Nighttime awakenings by a patient with dementia also can contribute to disturbed sleep in caregivers, researchers said.
"With that extra bit of sleep loss every night, maybe a caregiver now forgets some medication doses or reacts more emotionally than he or she otherwise would," said co-author Michael Scullin, Ph.D., director of Baylor's Sleep Neuroscience and Cognition Laboratory and assistant professor of psychology and neuroscience at Baylor.
Notably better sleep was observed in caregivers after such simple behaviors as getting more morning sunlight, establishing a regular and relaxing bedtime routine and taking part in moderate physical exercise.
For the analysis, researchers searched articles in peer-reviewed journals and books addressing caregivers, sleep, dementia and Alzheimer's disease, published through June 2018. Those studies measured sleep quality and quantity by monitoring brain electrical activity, body movements and self-reporting by caregivers.
The difference in time and quality of sleep was significant when compared to non-caregivers in the same age range and with the recommended minimum of sleep seven hours nightly for adults.
Researchers also analyzed intervention-related changes in sleep quality, such as daytime exercise, not drinking coffee or tea past late afternoon, not drinking alcohol at night and getting more sunlight in the morning.
"Given the long-term, potentially cumulative health consequences of poor-quality sleep, as well as the rising need for dementia caregivers worldwide, clinicians should consider sleep interventions not only for the patient but also for the spouse, child or friend who will be providing care," Gao opined.