depressionDepressed people are twice as likely as those who are not depressed to develop certain forms of dementia, such as Alzheimer’s disease, according to a new study in the July 6, 2010, issue of Neurology.
A health observer said caution needs to be exercised when interpreting the observations because the study merely revealed an association between depression and dementia; no evidence suggests a causal relationship.
For the study, researchers examined data on 949 people who were free of dementia but evaluated for depressive symptoms at baseline.  Average age of the participants was 79 when they were enrolled in the Framingham Heart Study.
At the beginning of the study, a total of 125 people, or 13 percent of the participants, were diagnosed with depression.  At the end of the 17-year follow-up, 164 participants had developed dementia; of those participants, 136 were diagnosed with Alzheimer’s disease.
The researchers found 22 percent of participants who had depression at the beginning of the study ended up developing dementia, compared to about 17 percent of those who were not depressed.
The trend held true after other factors were considered, including age, sex, education, and the APOE gene that is linked with increased risk of Alzheimer’s.
Jane Saczynski, PhD, author of the study from the University of Massachusetts Medical School in Worcester, MA acknowledged the study could not tell whether depression causes dementia or vice versa. However,  she said that depression might impact the risk of dementia in a number of ways.
For one thing, she said “Inflammation of brain tissue that occurs when a person is depressed might contribute to dementia. Certain proteins found in the brain that increase with depression may also increase the risk of developing dementia.”
“Several lifestyle factors related to long-term depression, such as diet and the amount of exercise and social time a person engages in, could also affect whether they develop dementia,” she added.
One real possibility, the health observer pointed out,  is that depression and dementia share some common cause.  He said vitamin D may be the link between the two.
Nanri A and colleagues from the International Medical center of Japan in Shinjuku-ku, Tokyo, Japan found that in November, people with  serum levels of vitamin D falling in the highest quartile were 49 percent less likely to experience depression.  The same association was also observed in winter, but not in July.
They published their study of 527 municipal employees aged 21 to 67 in the Aug 19, 2009 issue of European Journal of Clinical Nutrition.
C. D. Shipowick  of Washington State University in Richland, Washington and colleagues conducted a small trial and found that women who took vitamin D supplements experienced a decline in the Beck Depression Inventory -II scores suggesting that vitamin D helps depression.
They published the study in the Aug 2009 issue of Applied Nursing Research.
Additionally, vitamin D helps prevent dementia, such as that exhibited in those with Alzheimer’s disease.
Buell J.S. and colleagues,from Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, published a study in the Jan 5, 2010 issue of Neurology stating that elderly people with vitamin D insufficiency were twice as likely to have dementia, Alzheimer’s disease and stroke, compared to those with adequate levels of vitamin D.
The health observer suggested that it’s no use to blame depression for dementia and that it would be a mistake to try to treat depression in an effort to prevent Alzheimer’s.
He suggests that it is essential for us to find the causes that trigger depression and dementia and get rid of them; to do otherwise would merely treat symptoms.