New research suggests that the hepatitis B and C viruses may be linked to an increased risk of Parkinson's disease.

Carried out by a team from the University of Oxford, U.K., the study looked at hospital records from a large British database, including records of nearly 22,000 people with hepatitis B, 48,000 with hepatitis C, 6,000 with autoimmune hepatitis, 4,000 with chronic active hepatitis and nearly 20,000 with HIV.

These people were then compared to the hospital records of 6 million people with relatively minor conditions such as cataract surgery and knee replacement surgery.

For all participants, researchers also looked at hospital records to see who later developed Parkinson's disease.

The results showed that those with hepatitis B were 76 per cent more likely to develop Parkinson's disease than those in the comparison group, with a total of 44 people with hepatitis B later developing Parkinson's disease, compared to 25 cases that would be expected in the general population.

People with hepatitis C were 51 per cent more likely to develop Parkinson's disease, with 73 people developing disease, whereas around 49 cases would have been expected in the general population.

People with autoimmune hepatitis, chronic active hepatitis and HIV did not show an increased rate of Parkinson's disease.

Commenting on the results, study author Julia Pakpoor said, "The development of Parkinson's disease is complex, with both genetic and environmental factors. It's possible that the hepatitis virus itself or perhaps the treatment for the infection could play a role in triggering Parkinson's disease or it's possible that people who are susceptible to hepatitis infections are also more susceptible to Parkinson's disease."

Pakpoor also added that she hopes the new research will help the team better understand how Parkinson's disease develops, however she noted that the research had limitations, with the team unable to adjust for lifestyle factors such as smoking and alcohol use, which could increase the risk of developing the disease.

However the results do also support findings from a previous Taiwanese study which found a relationship between hepatitis C and Parkinson's disease, although the study did not show a relationship for hepatitis B.

Both hepatitis B and C viruses affect the liver.

Hepatitis B is spread through contact with blood and body fluids of an infected person, such as unprotected sex, sharing needles, getting a tattoo or piercing with unsterilized tools or sharing razors or toothbrushes with an infected person.

Hepatitis C is spread through blood-to-blood contact such as sharing needles, razors and toothbrushes and is passed on at birth by infected mothers.

The Centers for Disease Control and Prevention (CDC) estimate that anywhere from 850,000 to 2.2 million people in the United States have chronic hepatitis B virus infection and anywhere from 2.7 to 3.9 million people have chronic hepatitis C.

Many of those infected do not even realize they have the virus, due to showing only a few symptoms, however both can lead to serious illness.

The results can be found online published in the journal Neurology, the medical journal of the American Academy of Neurology.