People with mild cognitive impairment (MCI) who are depressed are more likely to develop Alzheimer's disease (AD) than people with memory problems who do not have depression, new research shows. Treating depression is known to delay the onset of AD. Treatment with a medication for AD also may delay progression to dementia in individuals with comorbid mood disorder, according to the study, which adds to growing evidence that links depression and dementia. 

    Researchers recruited 756 middle-aged and older adults with MCI and followed them for three years. In people with MCI, memory problems are worse than normal for their age group, but not severe enough to interfere with functioning. The study participants were assessed for depression with a test that employed a point system to indicate the severity of their symptoms. Researchers reported that about one-quarter of the study subjects had major depression, and that for every point increase on the depression test, the risk of developing AD over the three year study period increased by three percent. A comparison of participants with depression who were treated with donepezil (Aricept) and participants who received vitamin E or a placebo during the investigation revealed that over 2.2 years, people treated with Aricept experienced half the rate of progression to AD experienced by the other participants. The finding suggest that depression is a major risk factor for dementia among people with serious memory problems, and that Aricept might help delay disease progression significantly, study authors said in a report published in the June 16 issue of Neurology. 

    "There has been much anecdotal evidence that depression can accelerate progression to AD, and this is the first study that appears to validate that observation," says M. Cornelia Cremens, MD, a geriatric psychiatrist at the Senior Health Geriatric Medicine Unit at Massachusetts General Hospital (MGH). "It suggests that for people who have mild memory problems and depression, getting early treatment for either condition may help delay the worsening of memory problems and improve their quality of life."

 

    This study in Neurology adds to a body of research that suggests a strong association between depression and memory problems.  In April 2008, the American Journal of Geriatric Psychiatry published a study of 1,586 people aged 50 and older for up to 26 years, testing the levels of depression and cognitive functioning from time to time.  The researchers found that subjects who displayed symptoms of depression were more likely than subjects who were not depressed to have trouble with cognitive functions such as memory, attention, learning, decision-making, language and visuospatial function.

 

    Other studies suggest that depression may be a risk factor for AD--possibly because it is associated with brain changes that increase vulnerability to dementia--and that a history of depression can dramatically increase the risk for AD.  Research published in the April 8, 2008 issue of Neurology found that compared to similar adults who had never experienced depression, healthy individuals ages 60 to 90 who developed depression over a six-year period were two-and-a-half times more likely to develop AD; they were four times move likely to develop AD if they had experienced depression before the age of 60, the researchers found.  It is possible that risk for both AD and depression is increased by another unknown factor that may affect brain chemistry and structure.

 

    "The declines reported in depression and memory may work in concert," says Dr. Cremens.  "But whatever the underlying mechanism of this association, the good news is that depression in most people can be effectively treated with medication and talk therapy, and medications such as Aricept may help reduce the memory decline associated with depression and mild cognitive impairment in older people."

    Brain changes associated with depression include abnormal levels of chemicals that transmit messages between neurons, slowed activity in key memory regions of the brain, and atrophy of the brain's memory regions caused by excessive levels of stress hormones that slow neurogenesis, the generation of new nerve cells.

    The best way to avoid these changes is to keep your brain helathy and resistant to the damage created by depression, aging, environmental toxins and other factors, says Dr. Cremens.  The preserve brain health, she suggests people: