Dementia and depression can be constant companions in old age, but which comes first has been puzzling. The research literature is inconsistent, sometimes suggesting that declining mental powers plunge an older person into despair and other times supporting the idea that depression might pave the way for dementia.
A new study that followed participants in the long-running Framingham Heart Study lands squarely on side of depression as a risk factor for later dementia. Being depressed almost doubled the risk of dementia, Jane Saczynski of the University of Massachusetts Medical School and colleagues from Boston University report today in the journal Neurology.
To untangle the connection, the researchers tested 947 elderly people who had no signs of cognitive impairment at the start of the study. They were screened for depression at the outset and 125 scored high enough to be considered depressed.
Seventeen years later, 164 people had developed dementia, including 136 who were diagnosed with Alzheimer’s disease. Twenty-two percent of the people who were depressed at the study’s start developed dementia, compared with 17 percent who were not depressed. Looking at how people scored on the 60-point depression screening test, the researchers found that for each 10-point increase, there was a 50 percent increased risk of dementia. After accounting for age, sex, and other characteristics among the participants, depressed people were more than one and a half times more likely to develop dementia than people who were not depressed.
“We have such long follow-up in our study, it lends support to depression as a risk factor for dementia and not merely a consequence,” Saczynski said in an interview. “Everyone wants to find risk factors for dementia and know what increases risk. Here we identify one more risk factor.”
The study can’t say that depression causes dementia, Saczynski said, but it spurs greater interest in understanding what biological mechanisms might be related to both depression and dementia.
"The association between late-life depression and cognitive impairment does not appear to be spurious,” Dr. Yonas Geda of the Mayo Clinic writes in an editorial also appearing in Neurology, referring to the Saczyinski’s study and two others with consistent results. “However, there is insufficient evidence at present to support the hypothesis that depression has a direct causal relationship with subsequent dementia. Only a future mechanism of disease study with a biologic marker for depression can clearly identify which of the ... hypotheses is most pertinent.”
Meanwhile, doctors, patients, and family members can be alert to depression as a possible predictor of dementia, Saczynski said. They can also consider improving diet, sleep, and social engagement, factors that might help ease both depression and dementia. "It could be beneficial on both fronts," she said.
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