Depression in older adults has been found to be associated with an increased risk of cognitive decline and dementia.

3 to 63 percent of people with mild cognitive impairment show signs of depression, according to a new study. Other studies have shown that people who suffer from depression are at increased risk of developing dementia. However, why depression leads to dementia hasn't been cleared yet.

According to the National Institute of Mental Health, the risk of depression in the elderly increases with illness or when they lose ability to function independently. An estimated 1 to 5 percent of old people living in community centers suffer from major depression. The rate of depression increases to 13.5 percent in old people who require home healthcare and to 11.5 percent in elderly hospital patients.

The research included 2,160 community-dwelling Medicare recipients. Researchers led by Edo Richard, M.D., Ph.D., of the University of Amsterdam, the Netherlands evaluated the association between depression that sets later in life and incidence of mild cognitive impairment along with dementia.

Researchers found that depression was associated with mild cognitive impairment and dementia. People with mild cognitive impairment along with depression were at higher risk of dementia, especially vascular dementia, but not Alzheimer's disease.

"We found that depression was related to a higher risk of prevalent MCI and dementia, incident dementia, and progression from prevalent MCI to dementia, but not to incident MCI," the authors said.

"Our finding that depression was associated cross sectionally with both MCI and dementia and longitudinally only with dementia suggests that depression develops with the transition from normal cognition to dementia," the authors concluded.

The study is published in JAMA Neurology.