The greater the degree of depression, the more likely the impairment, the researchers found.
"This is important, because mild cognitive impairment often precedes dementia," notes lead author Deborah Barnes, PhD, MPH, a mental health researcher at SFVAMC. Approximately 50 percent of patients diagnosed with MCI go on to develop dementia within three years, according to the study authors.
The study also found no correlation between depression and vascular disease a significant finding, say the authors, because other researchers have hypothesized that vascular disease might lead to both depression and cognitive impairment by causing inadequate blood flow to different brain structures. "We found no evidence to support that hypothesis," reports Barnes, who is also an assistant professor of psychiatry at UCSF.
The study appears in the March, 2006 issue of Archives of General Psychiatry.
The researchers looked at 2,220 participants in the Cardiovascular Health Study, a longitudinal prospective study of adults 65 and older living in four American communities that is sponsored by the National Heart, Lung, and Blood Institute. The researchers measured the subjects' depressive symptoms using a standard depression scale. Six years later, the subjects were assessed for MCI by a team of dementia experts.
Ten percent of subjects with no depressive symptoms went on to develop MCI, and 13.3 percent of subjects with low depressive symptoms did. In contrast, 19.7 percent of subjects with moderate to high depression developed MCI after six years nearly twice the rate of subjects with no depressive symptoms.