After a diagnosis of Alzheimer's disease, families have much to worry about. They wonder what's next and how long their loved one has left to live.

A new study from UT Southwestern Medical Center in Dallas addresses those questions, finding that mental (cognitive) decline, age and other factors affect life expectancy after an Alzheimer's diagnosis.

The study authors say the findings could help improve planning for patients and their families.

"Life expectancy for patients with Alzheimer's disease typically ranges from three to 12 years but can be longer in some cases. Families are anxious to know what to expect and how to best plan for the time ahead in terms of finances, family caregiving, and how they want to live out their lives," said study co-author C. Munro Cullum, a professor of psychiatry, neurology, and neurological surgery.

"We're trying to get them better answers," Cullum explained in a UT Southwestern news release.

Cullum's team analyzed data from 764 U.S. patients with autopsy-confirmed Alzheimer's who died from the disease between 2005 and 2015. Their life expectancy after diagnosis ranged from one month to about 11 years.

The researchers determined that cognitive decline accounted for about 20% of the variance in patients' life expectancy. Cognitive functioning includes memory, attention, decision-making and problem-solving.

"We found that beyond global cognitive function, patients who were older, non-Hispanic, male, and who had more motor and psychiatric symptoms had a significantly shorter life expectancy," said study co-author Jeffrey Schaffert, a postdoctoral fellow in clinical neuropsychology.

The study was published recently in the Journal of Alzheimer's Disease.

Prediction of life expectancy in Alzheimer's patients is complex and affected by many factors, the researchers noted. They plan to further investigate the link between cognitive decline and life expectancy, and also hope to study a more diverse group of patients.

"This dataset was largely derived from well-educated white patients who donated their brains to research. We would like to extend this work to better reflect our more diverse patient population," Cullum said.