Suffering from bipolar disorder may put people at greater risk for Parkinson's later in life, new research reveals.
It's not yet clear what the underlying issues are adjoining the two brain disorders, but scientists suspect that factors like inflammation, genetics and miscommunications between brain cells.
Bipolar disorder affects some 5.7 million people in the US and becomes a severe impairment for the fixed majority of them at some point in their lives – more than any other mood disorder.
Parkinson's remains incurable and complications are the 14th leading cause of death in the US.
The researchers at the Taipei Veterans General Hospital in Taiwan hope that uncovering the link between the two devastating conditions may make them more treatable, or even altogether preventable.
People with bipolar disorder are about seven times more likely to develop Parkinson's disease later in life, according to a new study from Taiwan
The team followed over 56,000 people diagnosed with bipolar disorder between 2001 and 2009, plus another 224,360 who had never been diagnosed with the disorder, through 2011.
Several differences between the two became clear.
About seven times the proportion of people with bipolar disorder developed Parkinson's compared to those without the mood disorder.
To be exact, 0.7 percent of the bipolar group got Parkinson's, while only 0.1 percent of the non-bipolar group did.
Not only were people with bipolar disorder more likely to develop Parkinson's, but the symptoms came earlier in life.
The average Parkinson's patient without bipolar disorder was diagnosed at age 73, and those with bipolar were diagnosed almost a decade earlier, at 64.
The study's results, published in the journal Neurology, suggest that those with more severe bipolar may also be more prone to Parkinson's.
People who had hospitalized due to the mood disorder were more likely to develop Parkinson's.
And the more often they had to go inpatient, the more likely they were to develop Parkinson's.
The three percent of bipolar people who were hospitalized more than twice a year were at six-fold greater risk, and those hospitalized one or two times were four times more likely to start losing motor control than those with no mood disorder.
Few studies have looked into links between mood disorders at large and Parkinson's despite their shared neurological natures.
However, several have noted links between depression and Parkinson's.
In fact, depression is equally considered a warning sign of Parkinson's, because the disease alters brain chemistry in ways that can cause both tremors and depression.
Like depression and Parkinson's, scientists believe bipolar sufferers may, too, share roots in the inflammatory response.
Parkinson's is primarily marked in the brain by a shortage or dopamine.
While scientists have barely scratched the surface of understanding bipolar disorder causes, some have suggested that disrupted circadian rhythms and dopamine surges may explain the manic phases of bipolar disorder.
And the hippocampus, a part of the brain key to memory and managing emotions, seems to shrink more quickly in people with bipolar disease.
Scientists have seen signaling disruptions in the same part of the brain in Parkinson's disease patients.
But, ultimately, "further studies are needed to investigate whether these diseases share underlying processes or changes in the brain," said study author Dr. Mu-Hong Chen.
'These could include genetic alterations, inflammatory processes or problems with the transmission or messages between brain cells. If we could identify the underlying cause of this relationship, that could potentially help us develop treatments that could benefit both conditions. '