Red meat is a source of iron

A study found those who had high levels of both iron and manganese were almost twice as likely to develop the disease as those with the lowest levels of the minerals in their diets.

Spinach, legumes, nuts and whole grains are among foods which are rich in both iron and manganese.

Iron is also found in red meat and poultry.

It's too early to make any recommendations about potential dietary changes Dr Harvey Checkoway, University of Washington

Iron and manganese contribute to oxidative stress, where cells release toxic substances called free radicals as part of normal energy consumption and metabolism.

Free radicals cause tissue damage, and have been associated with Parkinson's disease.

The researchers stressed they were not advising people to stop eating these foods, but said their findings would increase understanding of how Parkinson's develops.

Supplements

The study, by University of Washington researchers, compared 250 people who had recently been diagnosed with Parkinson's to 388 people who did not have the disease.

They were interviewed to see how often they ate certain foods.

Those who had the highest level of iron in their diets , the top 25%, were 1.7 times more likely to have Parkinson's compared to those in the lowest 25% percent of iron intake.

If the level of both iron and manganese was higher than average, people were 1.9 times more likely to be Parkinson's patients than those in the lowest quarter.

Taking multivitamins or iron supplements increased the risk of those with a high level of iron or manganese in their diet even more.

Dr Harvey Checkoway, who led the research said: "Oxidative stress may cause degeneration of brain cells that produce dopamine - the same cells that are affected by Parkinson's disease."

He added: "Our findings may improve understanding of how Parkinson's disease develops.

"But, there are most likely numerous environmental, lifestyle and genetic factors that determine who will develop the disease. It's too early to make any recommendations about potential dietary changes."

The researchers said more studies were needed to confirm their findings.

Understanding

Robert Meadowcroft, director of policy, research and information for the UK's Parkinson's Disease Society, said: "We welcome research into the causes, treatment and cure for the condition.

"It is now accepted that the causes of Parkinson's are multifactorial. It is generally regarded in most cases as resulting from a combination of a genetic susceptibility and one or more environmental triggers.

"This is very early research and it should be stressed that while these findings may improve an understanding of how Parkinson's develops there are likely numerous environmental, lifestyle and genetic factors that determine who will develop the condition.

"We advise that further investigation be undertaken on this subject before any recommendations could be made on supplements and diet."