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According to the study, people with hepatitis B and C have a higher risk of developing the brain disorder. But that doesn't mean hepatitis causes Parkinson's disease. A neurologist explains.

April 19, 2017

You may have seen recent headlines tying hepatitis to Parkinson's disease. In a study published in the journal Neurology, researchers reported that people who have hepatitis B or C may have a higher risk of developing the neurodegenerative brain disorder.

But the finding shouldn't be cause for alarm, stresses Andrew Feigin, MD, professor of neurology at Northwell Health's Feinstein Institute for Medical Research in Manhasset, New York. It doesn't mean that hepatitis causes Parkinson’s, he says. Nor does it mean that having hepatitis automatically means you’ll get Parkinson’s. Far from it. Even if the data were confirmed, infection with the virus would just be another in the maze of risk factors that contribute to developing the disorder, which affects movement, mostly in people over the age of 60.

“There’s no one cause of Parkinson’s,” says Dr. Feigin, who was not involved in the new study. “There are a lot of different factors that lead up to one person having a risk and another person having a different risk.”

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The risks are both genetic and environmental. Two we know about are growing up on a farm and being exposed to pesticides; and growing up in very industrial areas with heavy metals in the air and water. Others are still unknown.

Hepatitis B is spread through blood and bodily fluids like semen, so unprotected sex, sharing needles, or even razors or toothbrushes can put you at risk. Hepatitis C is spread through contact with blood. Sharing needles, razors, and toothbrushes will put you at risk, but rarely does unprotected sex. Both viruses, if left unchecked, can damage the liver.

The authors, based in the United Kingdom, cross-referenced hospital records of people diagnosed with hepatitis and people with Parkinson’s disease. They found that people with hepatitis B had a 76% higher risk of developing Parkinson’s compared to people without the virus. The Parkinson's risk was 51% higher among those with hepatitis C. (Autoimmune hepatitis, chronic active hepatitis, and HIV weren’t linked to Parkinson’s.)

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The authors could only speculate on what might be responsible for such a relationship: the virus itself, the drugs used to treat the virus, or something else entirely.

They were not able to take into account lifestyle factors like smoking. And they acknowledge that using hospital diagnostic codes to categorize patients carries some uncertainties.

“Sometimes people with a diagnosis of Parkinson’s Disease really don’t have classic Parkinson’s,” explains Dr. Feigin. They have some of the same symptoms, like tremors; but the symptoms are often caused by something else, he adds. “You have to view [the data] with a bit of caution.”

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Even if the relationship between hepatitis and Parkinson’s pans out, there’s little need to panic. “Roughly .3% of the general population will get Parkinson’s at some point in their life,” says Dr. Feigin. “If the risk is even doubled, you’re still under a 1% likelihood of getting Parkinson’s." And in this study, the risk of developing Parkinson’s was less than double.