A new study found that people suffering from depression are more likely to develop dementia.

Earlier studies have linked depression to memory loss. People suffering from major depression do not only forget things, but also experience difficulty in task initiation, decision-making, planning, and thought organization. Researchers previously believed this was due to chemical imbalances in the brain that affected the region in which memories are stored. These probes were able to associate depression with memory loss, but failed to establish a direct correlation.

Study author Robert Wilson, senior neuropsychologist at the Rush Alzheimer's Disease Center at Rush University, worked with colleagues to conduct a new study in an attempt to establish a link between the two. The researchers involved 1,700 people aged, on average, about 77 years old. None of the participants were diagnosed with any cognitive or memory problems at the beginning of the study.

For an average of eight years, participants were examined for symptoms of depression such as demonstrated loss of interest in daily activities, appetite or weight changes, sleep changes, anger or irritability, and reckless behavior. They also took cognitive assessments to evaluate their thinking and memory skills.

During the follow-up period, 50 percent of the participants developed mild cognitive problems, while 18 percent were diagnosed with dementia. The researchers found that those who developed dementia also reported increased levels of depression prior to their diagnoses, but their depression started to decline after experiencing the cognitive disease.

"As people lose their thinking and memory skills, it becomes harder to become depressed and stay depressed," Wilson said to Healthday News. "Depression depends on a certain continuity of experience that becomes disrupted as you develop dementia. It's left to the rest of us to feel depressed as we watch our loved ones slip into dementia."

The researchers admitted that further study is needed to determine the structures and functions in the brain that cause depression in old age.

"That gives us a better chance of knowing how we should best treat depression in a way that will move the bar and reduce risk of dementia," he added.

The study was published in the July 30 issue of Neurology.