Depression can be an early warning of Parkinson’s and dementia, study finds

Researchers from Denmark have uncovered strong evidence that depression often appears years before Parkinson’s disease and Lewy body dementia. The team, led by first author Christopher Rohde, analyzed national health records and published their findings in the journal General Psychiatry. Their work suggests that changes in the brain linked to these disorders begin affecting mood long before movement or memory problems bring people to a neurologist.

Depression is already known to be common in both Parkinson’s disease and Lewy body dementia. About 30 to 40 percent of patients experience it at some point. When it appears alongside Parkinson’s disease, it is tied to brain volume loss, faster decline, poorer thinking skills, higher disability, suicide risk, and greater overall mortality. What scientists have not agreed on is why it starts. Some argue that slow damage to the brain causes mood problems early. Others think that early physical or cognitive symptoms create stress that leads to depression.

To sort this out, Rohde and his colleagues asked a simple question. Does depression show up earlier and more often in Parkinson’s disease and Lewy body dementia than in other long-term illnesses that also cause disability?

Their answer was yes, and by a wide margin.

The research relied on Denmark’s national health registers, which track hospital visits, diagnoses, and prescriptions for the entire population. Every person in the country has a unique ID number, allowing doctors and scientists to follow medical histories across many years.

The team identified everyone diagnosed with Parkinson’s disease or Lewy body dementia between January 2007 and January 2019. Parkinson’s disease was recorded under the code G20, and Lewy body dementia under G318E. They found 17,711 people in total, including 14,636 with Parkinson’s disease and 3,075 with Lewy body dementia. The median age was just under 75, and about 40 percent were women.

Each of these patients was matched with people of the same age and sex who were diagnosed with other chronic illnesses. The comparison groups included 19,556 people with rheumatoid arthritis, 40,842 with chronic kidney disease, and 47,809 with osteoporosis. These conditions often bring pain, disability, and frequent doctor visits, but they do not involve the same kind of brain degeneration.

Depression was not measured with surveys. Instead, it was identified through clear medical records. One signal was the first time someone filled a prescription for an antidepressant that was marked as treatment for depression. The other was the first time someone had a psychiatric hospital visit with a depression diagnosis. Whichever came first counted as the start of depression.

People were followed for as long as 10 years before and 10 years after their diagnosis. Not everyone had a full 20 years of data, but together the records created a wide window around the time each disease was identified.

The results showed that depression was much more common in people who later developed Parkinson’s disease or Lewy body dementia.

During the 10 years before diagnosis, 13.10 percent of future Parkinson’s patients developed depression. For Lewy body dementia, the figure was even higher at 16.91 percent. In comparison, only 5.56 percent of people with rheumatoid arthritis, 7.82 percent with chronic kidney disease, and 7.24 percent with osteoporosis developed depression in that same period.

After diagnosis, the pattern continued. Over the next 10 years, 7.93 percent of people with Parkinson’s disease and 8.49 percent of those with Lewy body dementia developed depression. The rates stayed lower in the other groups.

When researchers looked at the data year by year, the timing became even clearer. Depression rates began to rise about eight years before a Parkinson’s or Lewy body dementia diagnosis. The gap between these patients and the comparison groups widened as diagnosis approached. The highest risk appeared in the three years just before doctors named the disease.

The elevated risk did not fade right away. It stayed higher for up to five years after diagnosis. Lewy body dementia showed an even stronger link to depression than Parkinson’s disease in most of these years.

These trends held for both men and women. They also remained when Parkinson’s and Lewy body dementia patients were closely matched to people with rheumatoid arthritis of the same age and sex.

The findings point toward brain changes as a major driver of depression in these disorders.

Parkinson’s disease and Lewy body dementia affect several chemical systems in the brain. These include pathways that use serotonin, norepinephrine, dopamine, and acetylcholine. All of these play key roles in mood, motivation, and emotional control. When these systems begin to fail, depression can appear long before tremors, stiffness, or memory loss become obvious.

The even higher rates seen in Lewy body dementia may reflect its more aggressive course and heavier impact on the brain. Social stress and isolation may also add to the risk, but the early timing makes it hard to argue that depression is only a reaction to being sick.

Christopher Rohde from Aarhus University Hospital told The Brighter Side of News. “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. Thus, our main conclusion; that PD or LBD are associated with a marked excess depression risk preceding and following diagnosis when compared with other chronic conditions; remains valid.”

Because depression often appeared up to eight years before diagnosis, new depression in older adults deserves closer attention. With a typical diagnosis age around 75, late life depression may sometimes signal deeper brain changes rather than a stand alone mood disorder.

That does not mean doctors should start Parkinson’s drugs early. Those treatments can have serious side effects when used for long periods. It does mean doctors can watch patients more closely, offer mental health care sooner, and consider them for future trials aimed at slowing disease progression.

After diagnosis, the continued high risk of depression means mental health should be part of routine care. Depression is tied to faster thinking decline and worse overall outcomes. Treating it early may improve quality of life and possibly affect how the disease unfolds.

The study had some limits. Osteoporosis showed higher depression rates than expected, likely because it often follows painful fractures. Rheumatoid arthritis patients in Denmark may also receive less treatment for depression, which could affect comparisons.

The records mainly captured people treated in hospitals, so milder cases of Parkinson’s or Lewy body dementia may not be fully represented. Depression treated without medication or hospital visits was also missed. Still, these gaps apply across all groups and do not erase the clear pattern.

Research findings are available online in the journal General Psychiatry.

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