ADHD May Lead to Increased Risk of Parkinson’s

With no known cause, researchers continue to investigate how Parkinson’s disease (PD) develops in different kinds of people. Believed to be caused by a combination of environmental and genetic factors, PD generally develops after the age of 60. Retrospective investigations continue to evaluate the prior medical history of those who go on to develop Parkinson’s. A new study from the University of Utah finds a link between attention deficit hyperactivity disorder (ADHD) and the early onset of PD. In fact, the link was even stronger for those who were treated for ADHD with particular drugs.¹

Parkinson’s is a chronic, persistent neurodegenerative disorder traditionally characterized by motor symptoms. It can also result in significant non-motor, cognitive and other psychological impairments. ADHD is noted for uncontrolled hyperactivity and attention limitations in children. It is typically identified at an early age, and according to the Centers for Disease Control and Prevention (CDC), has been diagnosed in approximately 11% of children ages 4-17.³

ADHD, like Parkinson’s, is characterized by the deregulation of dopamine. Dopamine is a neurotransmitter that plays a role in regulating brain function; it helps to control movement and emotions. The depletion of dopamine can interfere with normal development in children and deterioration of nerve cells in adults.^2,4

Link between ADHD and Parkinson's

Study results published in Nature Neuropsychopharmacology discussed the correlation between ADHD and developing PD. For those diagnosed but not treated, there was a 2.5x increase in the likelihood for developing PD, or a Parkinson’s related disorder. For those that were treated with stimulants like Ritalin or other kinds of amphetamines, the increase spiked to a high of 8.6x.

Using the Utah Population Databases (UPDB), the analysis looked at 200,000 Utah residents with Parkinson’s (out of more than 11 million) born between 1950-1992. Within that population, around 32,000 had been diagnosed with ADHD. The review considered those at least 20 years old by 2011, who had no prior PD or PD-like diagnosis and excluded other known factors that might influence the development of PD.

The analysis looked at those who had been diagnosed with ADHD and received no known drug therapy. It also considered those who received stimulants like Adderall and others who were treated with methylphenidate (also known as Ritalin, Concerta, and other names). Researchers also looked at a control group of more than 150,000 people without ADHD who were matched by gender and age to the study population.

Psychostimulants

ADHD treatment generally uses medication and therapeutic stimulants to increase the amount of dopamine in the brain. The study results found the increase for those treated for ADHD was almost 4x higher than for those who did not have ADHD. It is possible that children with more severe kinds of ADHD could have a higher risk of developing PD for reasons which may, or may not, be related to taking medications.²

Findings

According to Dr. Glen Hanson, a professor at the University of Utah Health, this could be the first instance of childhood disease and its treatment is linked to a geriatric neurodegenerative disorder. Early onset PD, described in this study as being from age 21 to 66, was 8.6x higher in people with ADHD who were prescribed stimulant medications.²

Early findings presented in the literature address risk for developing Parkinson’s, both with and without the use of stimulant medication. These results suggest that we could yet see a increased rate of PD still to develop because the use of psychostimulant treatment for ADHD has increased over the last 20 years. This study echoes the findings of other research on amphetamine use and abuse, and its relationship to the development of PD.³

What’s next?

These results should be considered preliminary; the long-term effects of ADHD and its associated treatment have not been fully studied.⁴ Additional research on ADHD and its relationship to Parkinson’s is needed to more fully understand the correlations. It does appear, however, that ADHD increases the risk of developing Parkinson’s and Parkinson-like conditions over those with no history of ADHD.³