Before memory declines, people who will go on to develop Alzheimer's disease experience depression and behavioral changes, according to new research at Washington University School of Medicine in St. Louis.

Researchers have known that many people with Alzheimer's experience depression, irritability, apathy and appetite loss but had not recognized how early these symptoms appear. Pinpointing the origins of these symptoms could be important to fully understanding Alzheimer's effects on the brain and finding ways to counteract them.

"There has been conflicting evidence on the relationship between Alzheimer's and depression," Catherine M. Roe, senior author of the study, said in a statement. "We still don't know whether some of these symptoms, such as irritability and sadness, are due to people realizing on some level that they are having problems with memory and thinking, or whether these symptoms are caused directly by Alzheimer's effects on the brain."

For the study, Roe and her colleagues at the university's Charles F. and Joanne Knight Alzheimer's Disease Research Center analyzed data on 2,416 people ages 50 and older. Scientists regularly evaluated the participants for up to seven years, including how they performed in extensive tests of mental function and psychological health.

All of the participants were cognitively normal at the start, but over the course of the study, 1,218 of them developed dementia.

Researchers found that those who developed dementia during the study were more likely to have mood and behavioral changes first. For example, four years into the study, 30 percent of those who would go on to develop dementia had developed depression. In comparison, after the same period of time, only 15 percent of those who did not develop dementia during the study had become depressed. In addition, those who would go on to develop dementia were more than 12 times as likely to have delusions than those who did not develop dementia.

Alzheimer's researchers have been working to develop markers they can use to diagnose disease before the onset of dementia. The hope is to begin treating the condition before patients develop dementia.

However, Roe cautioned that the mood changes will not work well as markers in this regard until researchers better understand how these changes are connected to the disease.

The findings are detailed in the journal Neurology.