Hepatitis C, a liver infection caused by a virus, may increase the risk of developing Parkinson's disease, a common degenerative brain disorder.
"Many factors clearly play a role in the development of Parkinson's disease, including environmental factors," said study author Chia-Hung Kao from China Medical University in Taichung, Taiwan.
"This nation-wide study, using the National Health Insurance Research Database of Taiwan, suggests that hepatitis caused specifically by the hepatitis C virus may increase the risk of developing the disease. More research is needed to investigate this link," Kao explained.
The World Health Organization estimates that 130 to 150 million people have hepatitis C worldwide. While hepatitis C can lead to serious illness, many people have few symptoms and do not realise they have the virus, especially at first.
The virus is transmitted through sharing needles, needle stick injuries in health care providers and passed on at birth from infected mothers.
The study involved 49,967 people with hepatitis and 199,868 people without hepatitis. Participants with hepatitis were placed into three groups: those infected with the hepatitis B virus (71 percent), those with hepatitis C (21 percent), and those who had both viruses (8 percent).
The participants were followed for an average of 12 years to see who developed Parkinson's disease.
Of those with hepatitis, 270 developed Parkinson's disease, including 120 people with hepatitis C. Among those who did not have hepatitis, 1,060 developed Parkinson's disease.
The researchers found that people with hepatitis C were nearly 30 percent more likely to develop Parkinson's disease than the people who did not have hepatitis.
The study appeared in the online issue of the journal Neurology.
