More than 60 percent of people with dementia are also diagnosed with depression. In some cases, studies indicate that depression might even cause the brain to age faster. Both diseases have similar symptoms which occasionally lead to a mixed-up diagnosis. This has led many scientists and clinicians to seek to understand this connection.

Some of the questions researchers are now asking: Does depression always occur before dementia? And if so, is it part of the disease process—an early symptom of depression? Or does it have a causative relationship with the neurodegeneration that follows? We don’t yet know the answers, but we do know there are some very complex interactions between these two diseases.

There are a couple things we know that depression and dementia have in common: For starters, these diseases both occur at very high rates in older populations, both are complex in their origin, and neither is easy to treat. Here are a few other things we know so far:

Depression can cause cognitive impairment

When we think about the symptoms of depression, cognitive impairment hardly comes to mind. The most prominent symptoms include profound sadness, extreme fatigue and loss of joy.

But as many as three in five people diagnosed with depression will experience some form of memory loss or cognitive impairment. Depression affects working memory—the process that keeps important information handy in the short-term. It is responsible for remembering directions, names of people you’ve only just met, and also for more complex planning and thoughts.

Other effects of this cognitive impairment involve confusion, behavioral changes, and difficulty with doing everyday tasks. That sounds a bit like the early stages of dementia, doesn’t it? It is unsurprising that many people with depression are mistakenly diagnosed with dementia, while many with dementia are diagnosed with depression.

Depression is a risk factor for dementia

Many studies have found that people who are diagnosed with depression are more likely to develop dementia and experience earlier-onset of the disease. Treating depression also has a protective effect, reducing the risk of developing dementia later in life.

But since both of these diseases occur so often, figuring out whether they’re caused by similar processes in the brain is difficult. There may be common factors that contribute to the onset of both depression and dementia. Both depression and dementia are more likely to affect women. Both diseases also involve dysfunction in the brain’s immune system.

Dementia and depression are both treatable—but to varying extents

One big difference between these two diseases is that depression is easier to treat. While it may take one to two years of trying different medications and therapists, many people do go into remission.

On the other hand, there is currently only one disease-modifying treatment approved for Alzheimer’s — Biogen and Eisai’s drug Aduhelm—the efficacy of which is still controversial. Beyond the sheer question of whether it does in fact do what it was designed to do, the drug is difficult to access, not to mention expensive for people outside of clinical trials.

Speaking with a doctor and getting the right diagnosis is important for treatment. Some elderly people who are diagnosed with depression could experience more cognitive impairment when treated with some, but not all, antidepressants while others lower the risk of developing dementia.

Understanding depression may help us better understand dementia

There is even overlap in clinical trials, where researchers are looking at the effectiveness of depression treatments for some symptoms of dementia. A recent analysis found that the antidepressant drug fluoxetine may show promise in improving cognitive symptoms in Alzheimer’s.

Together, depression and dementia may be two of the most challenging medical issues that we face in the coming decades. However, learning what these two diseases have in common could help us treat depression and reduce the risk of some forms of dementia.

To learn about clinical trials of new medications that aim to modify the pathology of Alzheimer’s disease, call Charter Research at 407-337-1000 (Orlando) or 352-775-1000 (The Villages).