The link between depression and dementia is puzzling for researchers. Many studies have noticed a correlation between the two diseases and a 2013 review of 23 studies of about 50,000 older men and women reported that older adults suffering from depression were more than twice as likely to develop dementia and 65% more likely to develop Alzheimer’s.
But these have often only been associations. The newest study, published Wednesday in the journal Neurology, takes it further. The researchers believe that their findings, while not definitive, show that depression is in fact an independent risk factor for dementia, and not the other way around. Researchers looked at 1,764 people with no memory problems around age 77 and followed them for about eight years.
They discovered that people with mild cognitive decline as well as people with dementia were likely to have higher levels of depression symptoms before they were diagnosed, and that having these symptoms was associated with a greater decline in memory. Depression symptoms, the researchers estimated, accounted for 4.4% of the difference in memory decline that could not be caused by brain damage.