• Researchers investigated the association between late-life depression and dementia, and estimated the influence of depression treatments on the risk of dementia for patients with different courses of depressive symptoms.
  • Study participants with increasing, chronically low, and chronically high depression symptoms had a significantly higher risk of developing dementia than participants without depression or those with decreasing depression symptoms.
  • Depression treatments effectively lower the risk of dementia, especially in patients with increasing depression symptoms.
  • The findings indicate that providing timely depression treatment for those with late-life depression might postpone the onset of dementia.

In 2022, the World Health Organization classified dementia as the seventh leading cause of death among all diseases and estimated that around 55 million people worldwide live with this condition. Dementia can affect people physically, psychologically, socially, and economically, and this impact can extend to caregivers, families, and society at large.

Since there is currently no treatment available to cure dementia, its prevention is a priority. Several studies have shown that depression raises the risk of dementia. Therefore, the timely treatment of depression might help to prevent it.

Typically, depression is treated using pharmacotherapy, psychotherapy, or a combination of both. Although there have been studies on whether pharmacotherapy for depression lowers the risk of later-life dementia, the results have been mixed, with some studies reporting positive outcomes, and others yielding negative or neutral results.

A 2017 study found that administering selective serotonin reuptake inhibitors for more than 4 years decreased the risk of people with mild cognitive impairment developing dementia.

Conversely, another 2017 study found that the use of antidepressants did not make a difference in the risk of dementia, while a 2016 study concluded that antidepressant use in the elderly was associated with an increased risk of dementia.

None of these previously published studies takes into account the fact that different individuals experience different depression trajectories (or patterns of depression symptoms over time).

Now, researchers at Fudan University in Shanghai, China, have published a study in Biological Psychiatry, that examines the relationships between different depression trajectories, different depression treatments, and the likelihood of developing dementia.

“This is very interesting. As we have said before (all laid out in the 2020 Lancet Commission on dementia), few previous studies have distinguished between treated and untreated depression. […],” said Dr. Gill Livingstone, professor of psychiatry of older people at University College London, and leader of the Lancet Commission on dementia, prevention, intervention and care, who was not involved in the study.

“This study here follows up people with depression aged over 50 for 10 to 14 years [and like a previous study] finds a nearly identical increased risk of dementia (51%). This was particularly true for those who had depressive symptoms or got worse over time, [while] those who were treated and were not highly depressed had a reduction i[n] risk,” she told Medical News Today.

“This is an important finding and suggests people in mid to late life with depression should be treated energetically to improve symptom[s], helping their quality of life and decreasing their likelihood of developing dementia.”
— Dr. Gill Livingstone

Between 2006 and 2010, the study enrolled 354,313 individuals from the UK Biobank ages between 50 and 70. 189,440 participants (53.5%) were women.

A total of 46,280 participants were diagnosed with late-life depression at baseline, of whom 725 developed dementia during the follow-up period. The researchers followed up with the participants until 2020.

To study the effect of different depression trajectories on the rate of dementia, the researchers identified 4 subgroups. Those with:

  • increasing depression symptoms over time (n = 3,462)
  • decreasing depression symptoms over time (n = 3,578)
  • chronically high depression symptoms (n = 2,281)
  • chronically low depression symptoms (n = 3,159)

To examine whether the risk of developing dementia can be lowered by treating depression, the researchers further categorized the 46,820 participants with depression into the following treatment groups:

  • untreated (n = 24,152)
  • pharmacotherapy (n = 14,695)
  • psychotherapy (n = 2,151)
  • combination (n = 5,281)

As expected, the researchers found that study participants with depression had a 51% higher risk of dementia than those without depression.

Within the subgroup of participants with depression, the risk of developing dementia differed depending on their depression trajectory. Individuals with ‘increasing’, ‘chronically high’ and ‘chronically low’ depression symptoms had a higher risk of developing dementia, whereas individuals with ‘decreasing’ levels of depression had the same dementia risk as individuals without depression.

The researchers found that depression treatments are associated with a lower incidence of dementia, with an approximately 26% lower risk of dementia among patients who received treatment.

Furthermore, the researchers observed that, although an ‘increasing’ depression trajectory raises the risk of dementia most quickly, taking depression therapies could counteract the rising risk. On the other hand, depression treatments had no effect on the risk of dementia in individuals with a chronically high level of depression.

This finding highlights the importance of prompt diagnosis and treatment for depression, not only for the sake of keeping depression under control, but also to reduce the patient’s risk of dementia.

Dr. Wei Cheng, study co-leader and a young principal investigator at the Institute of Science and Technology for Brain-Inspired Intelligence (ISTBI) at Fudan University, says the findings from this study “shed some light on previous work as well. The differences of effectiveness across depression courses might explain the discrepancy between previous studies.”

When commenting on study limitations, the researchers note that studies so far have “proved inconclusive that whether depression is a prodromal phase (symptom) or an independent risk factor for dementia..” Thus, they say the link between depression and dementia “should still be interpreted with caution.”

Dr. Livingstone reiterated this in her comments to MNT: “Depression might be a risk for dementia, but, in later life, dementia might cause depression.”