Dementia and Depression: A Connection
For a long time, scientists assumed dementia and depression had nothing to do with each other. The questions kept piling up anyway. Does one bring on the other? Do they arise separately, or do they hit the same parts of the brain at the same time? Recent work points toward an answer that is less tidy than a simple cause and effect: depression appears to raise a person's risk of developing dementia.
Dementia itself is a broad label rather than a single illness. It covers a drop in mental ability across things like memory, concentration, communication, and the ordinary tasks of a day. Alzheimer's disease is the version most people have heard of. To reach a diagnosis, doctors lean on physical exams, lab results, a patient's medical history, and tests that track behavior and memory. Often they can confirm that dementia is present without being able to pin down which subtype it is.
What drives dementia is damage to brain cells. Once those cells are injured, they stop talking to one another properly, and the fallout spreads into different areas of functioning. Where the damage sits in the brain tends to line up with which form of dementia a person has. Alzheimer's, for example, is tied to harm in the hippocampus, the region that handles memory and learning.
Injure the cells in the hippocampus and the signals start to break down: how to pick up a new skill, how to carry out something already learned, even the recognition of a familiar face. The hippocampus does double duty, though, because it also plays a part in regulating mood. Brain scans of people living with depression sometimes show a hippocampus that is smaller than in people who have never been depressed. A shrunken hippocampus holds fewer serotonin receptors, and trouble with serotonin, both producing it and receiving it, is one of the roots of depression for a lot of people. That overlap is why growing new cells in the hippocampus may matter for treatment.
A study in Science laid out how neurogenesis, the creation of new brain cells, in the hippocampus can pull depressive symptoms down. The researchers were testing antidepressant drugs on lab animals when they noticed the drugs pushed neurogenesis up. The timing was telling: the cell growth took about as long to appear as antidepressants take to work in adult humans, which suggested it mirrored what happens with adult human neurogenesis. They then looked at neurogenesis in stressed primates and found stress held cell growth back. Add antidepressants and the growth leveled out again.
So why does any of this count? Two threads tie together. The hippocampus in depressed patients tends to be smaller, and that same region manages both mood and memory. If new cell growth there can lift mood and memory, and if antidepressants can spur that growth, then antidepressants, along with treatments still to come that target hippocampal growth, start to look promising. Depression and its remedies vary from one person to the next, but a treatment that works by encouraging cell growth in the hippocampus might do two jobs at once, easing the depression while giving memory a lift.
The risk running in the other direction is real too. Research out of Rush Medical Center found that people with depression carry a higher risk of dementia later on. Among the depressed participants in that work, 52% went on to develop Mild Cognitive Impairment and 18% developed dementia. The people who ended up with MCI or dementia usually had more severe depressive symptoms before those diagnoses arrived.
A Mayo Clinic study of patients with Alzheimer's and Lewy body dementia pointed the same way. Participants who already had Mild Cognitive Impairment plus depression were 66% more likely to progress to dementia than those who had MCI without depression. Put together, the numbers suggest that treating depression, and heading it off where possible, could help prevent or ease what MCI and dementia bring.
On the treatment side, a handful of approaches tend to come up. Exercise and physical activity have shown they can ease depression, and they offer something to people dealing with dementia as well, sharpening cognitive function, smoothing out sleep cycles, and leaving people with more energy.
Building structure into the day can help with depression too, partly by restoring a sense of control. That same routine can support memory. Classes, games, reading, writing, and sitting with photographs of loved ones all carry a therapeutic payoff and give cognitive activity a workout.
Time spent with other people does more than open the door to relationships and small pleasures; the act of communicating itself ramps up brain activity. Having something social to look forward to can cut down on isolation, which otherwise feeds both cognitive and mood problems.
Psychotherapy and group therapy can be part of the recovery. They hand people concrete strategies for working through depression and dementia, and they can take the edge off the feeling of being alone in it.
SSRI medications are another option. Drugs in that class (selective serotonin reuptake inhibitors such as Celexa, Zoloft, Lexapro, and Prozac) can round out the therapies above, though they do not stand in for them. Leaning on SSRIs alone while ignoring everything else can invite complications. Not every person needs medication or responds to it, and finding the right match for the individual takes care. Where it fits, though, medication can improve how the brain takes in and produces the chemicals that quiet the symptoms of both depression and dementia.
- Melissa Lavery, M.S.