(CBS News) A new study shows that middle-aged and elderly men and women who suffer from depression may be at a higher risk of developing dementia.
The results, published in the May 2012 issue of the Archives of General Psychiatry, showed that those who had depression symptoms in the later stages of life were 70 percent more likely to develop dementia than those who didn't have symptoms during that time.
"Depression commonly occurs in individuals with cognitive impairment and dementia," the researchers wrote. "Although some studies have found that depression coincides with or follows the onset of dementia in older adults, most studies and several meta-analyses have concluded that depression precedes dementia and is associated with approximately a 2-fold increase in the risk of developing cognitive impairment or dementia."
According to the National Institute of Health, dementia - also known as senility - is the term for a group of disorders that affect cognitive functions of the brain. Common symptoms include memory loss and problems with brain functions like the ability to speak.
The most common form of dementia is Alzheimer's disease. The Alzheimer's Association reports that 5.4 million Americans live with the disease, including one in eight older Americans. It is the sixth-leading cause of death in the U.S. and is the only illness in the top 10 that cannot prevented, cured or slowed.
Researchers followed 13,535 starting from when they were 40 to 55 for over 50 years who were part of the Kaiser Permanente Medical Care Program of Northern California. Between 1964 and 1973, the participants were examined about their behaviors, medical histories and a detailed record of their basic statistics were recorded. From there, they determined which of the individuals were depressed. They checked in on them between 1994 and 2000 and then finally from 2003 to 2009, when the mean subjects age was 81.
Depressive symptoms were present in 14.1 percent of subjects during their midlife, 9.2 percent in late life only, and 4.2 percent in both stages. During the six years they had follow-ups, 22.5 percent were diagnosed with dementia. About 5.5 percent were diagnosed with Alzheimer's disease, caused by protein deposits that stop brain function, and 2.3 percent were determined to have vascular dementia, which is caused by blood flow being blocked from the brain.
The chance of getting dementia increased by approximately 20 percent for those who had midlife depressive symptoms, 70 percent for those who had for late-life symptoms only, and 80 percent for those who exhibited the symptoms in both periods. Depressive symptoms in mid and late stages showed double the risk from Alzheimer's, while the risk for vascular dementia increased threefold.
The researchers commented that future studies are necessary to determine if depression treatment during mid and late stages can help stave off dementia.
"Given the anticipated increase in dementia prevalence during the next 40 years, even a small reduction in dementia risk would have a tremendous public health impact," they wrote.