Depression Could Increase Risk of Parkinson Disease

The link between depression and Parkinson disease (PD) has been well documented. According to the National Parkinson Foundation, it is estimated that 50% of patients diagnosed with the disease will experience some form of depression during the course of their illness.¹ Unfortunately, in people “. . .with depression and Parkinson’s disease, each illness can make symptoms of the other worse. For example, people with both illnesses tend to have more movement problems and greater levels of anxiety than those who have just depression or Parkinson’s disease.”² In a recent, large cohort study, lead author Peter Nordström, PhD and colleagues reported that depression is associated with an increased risk for PD.³

The researchers found 140,688 cases of depression in the Swedish population aged 50 years or older. The group was matched 1:3 with control subjects not diagnosed with depression, for a total of 562,631 participants who were followed for an average of 6.8 years. At a median of 4.5 years after enrollment, 3,260 people were diagnosed with PD: 1.1% from the group diagnosed with depression and 0.4% from the control group. “The link between depression and subsequent Parkinson’s disease appears to be strongest in the few years before the onset of motor symptoms, but depression may exist earlier.”⁴

Serious cases of depression increased the likelihood of PD. Those hospitalized 5 or more times for depression were 40% more likely to develop PD than those hospitalized only once. Also, hospitalized depression patients were 3.5 times more likely to develop PD than people treated for depression as outpatients.⁴

A subcohort of 540,811 sibling pairs was also included in the study to determine possible confounding, but siblings’ depression was not found to be significantly associated with PD risk. “If the diseases were independent of each other but caused by the same genetic or early environmental factors, then we would expect to see the two diseases group together in siblings, but that didn’t happen.”⁴

Due to the timing of depression and subsequent PD diagnosis, the link between recurring depression and subsequent PD diagnosis, as well as the lack of a link between siblings’ depression and PD, it is possible that depression could be an early symptom or a risk factor of PD. “It could be that depression damages the brain, causing the increase in Parkinson’s,” Dr. Nordstrom said. “Or it could also be that very early in Parkinson’s, we are more prone to depression. It’s impossible to say.”⁵

References:

1. National Parkinson Foundation. Depression. http://www.parkinson.org/Parkinson-s-Disease/Living-Well/Depression. Accessed 1 June 2015.

2. National Institutes of Health. Depression and Parkinson’s disease. http://www.nimh.nih.gov/health/publications/depression-and-parkinsons-disease/index.shtml. Accessed 1 June 2015.

3. Gustafsson H, et al. Depression and subsequent risk of Parkinson disease. Neurology. Epub ahead of print 20 May 2015.

4. Lowry F. Depression may be harbinger of Parkinson’s. Medscape Medical News. 28 May 2015. http://www.medscape.com/viewarticle/845497?src=wnl_edit_tpal&uac=240755CV#vp_2

5. Bakalar N. Depression tied to increased risk of Parkinson’s disease. Well Blog, New York Times. 20 May 2015.  http://well.blogs.nytimes.com/2015/05/20/depression-tied-to-increased-risk-of-parkinsons-disease/?_r=0.