This is a large observational study — meaning the researchers watched what happened in a real population without testing any treatment. They used Korea's national health insurance records (which cover almost everyone in the country) to count how many new cases of Parkinson's disease and dementia were diagnosed each year from 2003 to 2023. Counting new cases over time is called incidence (as opposed to prevalence, the total number living with a condition at any one moment).
The headline finding is that the two diseases moved in opposite directions. New Parkinson's diagnoses dropped modestly but steadily — from about 16.6 to 11.4 per 100,000 people per year (roughly a 2% annual decline). New dementia diagnoses climbed steeply from 2003 to 2012 (from ~42 to ~172 per 100,000), then fell back somewhat after 2018 to ~113 — but over the full 20 years the overall trend was still a large net increase. Both diseases peaked in people in their 70s and 80s. Dementia also fell unevenly across society: women, rural residents, and low-income ('medical aid') recipients were diagnosed more often and had the shortest time before receiving a diagnosis.
For someone living with Parkinson's, this study does not test a drug or therapy and changes nothing about today's treatment options. The falling Parkinson's numbers may partly reflect shifting diagnosis practices rather than a true drop in cases, so it is not proof the disease is becoming rarer. The clearest message is about inequality of access: if you or a loved one lives rurally or has limited income, diagnosis and support may come later. That is worth raising proactively with a clinician — asking for timely cognitive screening and help connecting to support services rather than waiting.