While caregivers may find their work rewarding and necessary, the everyday stress can take a toll on their mental well-being. Up to 40 percent of dementia caregivers suffer from depression. They also report above-average levels of anxiety, social isolation and frustration.

"We were able to meet and speak with a number of caregivers, many of whom talked about the challenges of watching their spouse or loved one slowly lose their sense of self and their ability to live independently," said study co-lead author Sandy Lwi.

The study notes that poor mental health in caregivers can can reduce the quality of patient care by raising the risk of neglect or abuse, weaken the patients' immune systems by compromising social bonds between the caregiver and patient, or transmit negative emotions directly to patients through a phenomenon known as emotion contagion, in which one person in a relationship absorbs the emotional responses of the other.

In the United States alone, more than 7 million people are estimated to suffer from neurodegenerative disorders such as Alzheimer's, frontotemporal dementia, Parkinson's, multiple sclerosis, Lou Gehrig's (ALS) and Huntington's disease, all of which lead to gradual declines in cognitive, emotional and motor functioning.

The unrelenting progression of these diseases, with a rate of survival ranging from three to 10 years after initial diagnosis, means that patients are often cared for in the home by relatives or close friends who are not being paid for their work.

Researchers said they will continue to check in on the surviving caregiver-patient relationships in their study to dig deeper into the dynamics at play.

"Soaring rates of dementia and other neurodegenerative diseases constitute one of the most pressing public health challenges of the present era, and this will become even more challenging as the population ages," Levenson said in a news release from UC Berkeley on Monday.