MONDAY, May 7, 2012 (HealthDay News) -- People who suffer depression when they're middle-aged or elderly may also have an higher risk of dementia later, a new study suggests.
Researchers evaluated long-term data from more than 13,000 people in California. They found that depressive symptoms occurred in about 14 percent of participants in midlife only, while about 9.2 percent of cases of depression developed in late life only. Just over 4 percent of people in the study had depression that stretched over midlife and late life.
Over six years of follow-up, 22.5 percent of the participants were diagnosed with dementia. The study found that 5.5 percent of the participants developed Alzheimer's disease and 2.3 percent developed vascular dementia, which is caused by brain damage resulting from impaired blood flow to the brain.
According to the research team, people with late-life depression were twice as likely to get Alzheimer's disease and those with both midlife and late-life depression had a more than threefold increased risk of vascular dementia.
The research team was led by Deborah Barnes, of the University of California, San Francisco, and the San Francisco Veterans Affairs Medical Center. Writing in the May issue of the Archives of General Psychiatry, they say the findings suggest that depression extending throughout the lifespan might raise odds for dementia, especially vascular dementia. In many cases, depression occurring for the first time in late life may reflect an early stage of dementia, especially in the case of Alzheimer's disease.
The study was only able to find an association between depression and Alzheimer's risk; it could not prove cause-and-effect.
More than 5 million people in the United States have Alzheimer's disease and the health care costs of the condition were about $172 billion in 2010, according to background information in the study.
"Prevalence and costs of Alzheimer's disease and other dementias are projected to rise dramatically during the next 40 years unless a prevention or a cure can be found. Therefore, it is critical to gain a greater understanding of the key risk factors and etiologic [causal] underpinnings of dementia," the researchers wrote.
The U.S. National Institute of Neurological Disorders and Stroke has more about dementia.