A study, conducted by researchers at the San Francisco VA Medical Center ( SFVAMC ) and the University of California - San Francisco ( UCSF ), found that older adults with depressive symptoms are more likely than those without depression to develop mild cognitive impairment ( MCI ) within six years.

" This is important, because mild cognitive impairment often precedes dementia," notes lead author Deborah Barnes, at SFVAMC. Approximately 50 percent of patients diagnosed with MCI go on to develop dementia within three years.

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.

The study is published in the 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 ( NHLBI ). The researchers measured the subjects' depressive symptoms using a standard depression scale.
Six years later, the subjects were assessed for mild cognitive impairment by a team of dementia experts.

Ten percent of subjects with no depressive symptoms went on to develop mild cognitive impairment, and 13.3 percent of subjects with low depressive symptoms did.
In contrast, 19.7 percent of subjects with moderate to high depression developed mild cognitive impairment after six years, nearly twice the rate of subjects with no depressive symptoms.
The findings were consistent among all subgroups in the study, men and women, younger and older, with and without vascular disease, and regardless of education level.

One major implication of the study, according to Barnes, is that family members and health care providers should pay attention when an older person seems newly depressed. " Even if they don't have cognitive impairment at that time, our study suggests that you probably want to keep an eye on them," she says. " Depression might be an early sign of neurodegeneration – in fact, it might be the first symptom that a family member notices."

Kristine Yaffe, at SFVAMC and the principal investigator of the study, says the next step is to investigate whether treating older adults with newly diagnosed depressive symptoms might be effective in preventing the development of mild cognitive impairment. " Perhaps getting a family member in for early treatment would make a difference," she speculates. " We don't know the answer yet, but I think it's important to evaluate."

Barnes says she would also like to see other researchers investigate the reasons for the association between depression and mild cognitive impairment. "I f vascular disease is not the mechanism, what is ? " she asks. " One theory is that people who are undergoing stress or experiencing depression often have elevated levels of the stress hormone cortisol. There is growing evidence that this may lead directly to brain damage in the hippocampus," a part of the brain that plays a significant role in memory and Alzheimer's disease.

Source: University of California - San Francisco, 2006


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