People suffering from depression may face a higher risk of developing dementia later in life and suffering from cognitive issues, according to a new study published in Neurology.

"We've known for a long time that people with some depression are more likely to develop cognitive decline and dementia in old age than people without depression," said the study's lead author Robert S. Wilson, PhD, neuropsychiatrist at the Rush Alzheimer's Disease Center.

"But dementia takes a long time to develop, more than a decade, and there's been school of thought that depression was perhaps an early sign of the development of dementia and not a true risk factor. Here we show that is definitely not the case," said Wilson.

The study also reveals that as dementia sets in patients suffering from depression saw a decrease in depression symptoms and behavior. That goes against earlier studies that indicated depression and dementia might be link to a brain abnormality.

"We found that people did not become more depressed and some even became less depressed after they developed dementia," said Wilson. "Furthermore, depression was not related to the common brain [abnormalities] that really drive dementia in old age. So depression appears to be a genuine risk factor for cognitive decline."

The study's 1,764 participants averaged the age of 77 and were not suffering from any cognitive or memory issue. They were screened annually for eight years for depression, as well as symptoms such as loss of appetite and loneliness as well as memory skills. During the study 680 people died.

"These were not necessarily people who were going to see a psychiatrist for their condition," said Wilson. "The message is that mild to moderate depressive symptoms make a difference by the time you reach old age, so we should think about more aggressively treating these less severe cases."

The Centers for Disease Control and Prevention reports 28 million Americans are suffering from depression, with those between the ages of 45 to 64 at greatest risk.

During the eight years of research 52 percent developed mild cognitive impairment, and 18 percent developed dementia.

Researchers say further studies are needed to investigate the connection between depression and dementia.

"Research has shown for years that if you place animals under chronic stressful conditions, a series of changes in the brain occur that are linked to elevated levels of stress hormones," said Wilson. "Most people think that it's the higher levels of stress hormones that are at least partially responsible the connection between depression and cognitive decline."

A related report indicates Americans over the age of 60 face a 44 percent lower chance of developing dementia than a 60-year-old did three decades ago.