Are Depressed Patients at Greater Risk for Parkinson’s Disease?

A team of Swedish researchers has found that individuals with depression may be more likely to develop Parkinson’s disease.

Investigators from Umea University used a cohort including all Swedish citizens age 50 and older as of Dec. 31, 2005, taking from this group 140,688 individuals diagnosed with depression between the years 1987 and 2012. These patients were each matched with 3 control participants—a total of 421,718 controls—of the same age and sex who had not been diagnosed with depression.
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The researchers followed participants for up to 26 years. In that time, a total of 1,485 individuals with depression, or 1.1% of participants, developed Parkinson’s disease. In comparison, 1,775 participants who did not have depression, or 0.4%, were diagnosed with Parkinson’s in that same span. On average, Parkinson’s disease was diagnosed 4.5 years after the beginning of the study, with the likelihood of the disorder developing decreasing over time. The investigators determined that those with depression were 3.2 times more likely to develop Parkinson’s disease within a year of the study’s start, with those same individuals becoming nearly 50% more likely to develop Parkinson’s over the course of 15 years to 25 years.

The findings have “no clear implications for primary care practitioners, for more than one reason,” says Peter Nordstrom, PhD, a professor and chief physician in the department of community medicine and rehabilitation at Umea University, and co-author of the study.

For example, the risk of Parkinson’s disease remains small even after experiencing depression, and “we don’t know that depression actually causes Parkinson’s disease,” he says, noting that depression may be a very early sign of Parkinson’s, “although that might be less likely.”

In addition, the types of drugs typically used to treat depression, such as Prozac, are “actually quite ineffective, and any effects, although quite small, have only been demonstrated in severe depression, which only constitutes a very small proportion of all depressions.”

—Mark McGraw

Reference

Gustafsson H, Nordstrom A, et al. Depression and subsequent risk of Parkinson disease: A nationwide cohort study. Neurology. 2015.