The Taiwanese health database was used to identify 2 groups of people, those with and without bipolar disorder. The researchers found that, during a 2-year follow-up period, ~0.7% of those with bipolar disorder went on to develop Parkinson's, compared with just ~0.1% of the control group.
A common link
We know that changes in mood, particularly depression, are a common non-motor symptom in Parkinson's. And a nationwide Swedish study reported an association between Parkinson's and major depressive disorder.
While the exact cause of bipolar disorder is unknown, it's thought that an imbalance of chemical signalling in the brain, including altered levels of dopamine, may be to blame. But the reason that these changes could increase the risk of developing Parkinson's remains unclear.
A large scale study
This nationwide study is the first to investigate the relationship between Parkinson's and bipolar disorder across a large group of people. The researchers examined 56,340 people diagnosed with bipolar disorder between 2001 and 2009, alongside 225,360 people who did not have the condition. They found that a higher percentage of people with bipolar went onto develop Parkinson's compared with the control group.
And after taking into account other factors that could affect the risk, such as age and the use of antipsychotic medications, the researchers reported that people with bipolar disorder were at a higher risk of developing Parkinson's (almost 7 times more likely). This risk was also seen to be associated with the severity of the bipolar disorder.
Dr Lynn Duffy, Senior Scientific Copy Writer at Parkinson's UK said:
"We know that dopamine plays a complex role in brain signalling, from coordinating movement to regulating our moods. So it's perhaps not surprising that there are links between conditions such as Parkinson's and bipolar disorder, where dopamine signalling is disturbed.
"Further research into what connects these 2 conditions could help in the development of treatments for both Parkinson's and bipolar disorder."
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