Depression may be the brain’s early warning sign of Parkinson’s or dementia

Drawing on comprehensive Danish national health registers, the researchers conducted a retrospective case–control study including 17,711 individuals diagnosed with PD or LBD between 2007 and 2019. Researchers compared these patients with people of similar age and sex who were diagnosed with other long-term conditions, including rheumatoid arthritis, chronic kidney disease, and osteoporosis.

The results showed a clear pattern: depression occurred more often and earlier in people who went on to develop Parkinson’s disease or Lewy body dementia than in those with other chronic illnesses. In the years leading up to diagnosis, the risk of depression rose steadily, peaking in the three years before diagnosis. Even after diagnosis, patients with Parkinson’s disease or Lewy body dementia continued to experience higher rates of depression than the comparison groups.

Importantly, this pattern could not be fully explained by the emotional burden of living with a chronic illness. Other long-term diseases that also involve disability did not show the same strong increase in depression risk. This suggests that depression may be linked to early neurodegenerative changes in the brain, rather than being only a psychological reaction to declining health.

The findings were especially striking for Lewy body dementia, where rates of depression were even higher than in Parkinson’s disease, both before and after diagnosis. Researchers note that differences in disease progression and brain chemistry may help explain this trend.

"Following a diagnosis of PD or LBD, the persistent higher incidence of depression highlights the need for heightened clinical awareness and systematic screening for depressive symptoms in these patients." first author Christopher Rohde noted "Thus, our main conclusion—that PD/LBD are associated with a marked excess depression risk preceding and following diagnosis when compared with other chronic conditions—remains valid."

The authors emphasize that this does not mean everyone with depression will develop Parkinson’s disease or dementia. Instead, they recommend greater awareness and closer monitoring when depression appears for the first time in older adults.

While there is currently no cure for Parkinson’s disease or Lewy body dementia, addressing depression early could improve quality of life and overall care for patients as these diseases develop.