A high intake of iron, especially in combination with high manganese intake, may be related to risk for Parkinson's disease, report scientists in the US.
Researchers from the University of Washington School of Medicine, Seattle, assessing the impact of dietary nutrients on the disease, found that a higher than average intake of iron and manganese almost doubled the risk for the disease, while antioxidants and fats had no apparent effect.
The researchers studied food frequency habits in a population-based sample of 250 people with newly diagnosed Parkinson's and used a control group of 388 subjects, frequency matched to cases on sex and age.
Interviews were conducted to produce data on eating habits during adulthood. Nutrient intakes were calculated by adjusting each person's nutrient intake by their total energy intake (the nutrient density technique).
People who had higher than average dietary iron intake and who also took, on average, one or more multivitamins or iron supplements per day were 2.1 times more likely to be Parkinson's patients than those who had lower than average dietary iron intake and who took fewer than one multivitamin or iron supplement per day, said the team.
And those who had higher than average dietary manganese intake and also took an average of one or more multivitamins per day were 1.9 times more likely to be Parkinson's patients than those who had lower than average dietary manganese intake and who took less than one multivitamin per day, reported the researchers in this month's Neurology. Foods rich in both iron and manganese include spinach, legumes, nuts and wholegrains. Iron is also abundant in red meat and poultry.
Iron and manganese are known to contribute to oxidative stress, when cells release toxic free radicals as part of normal energy consumption and metabolism.
"Oxidative stress may cause degeneration of brain cells that produce dopamine - the same cells that are affected by Parkinson's disease," explained study author Dr Harvey Checkoway from the University of Washington in Seattle.
While the study at first seems to further reveal the risks of overdosing on supplements, Checkoway stressed that the benefits of eating foods rich in iron and manganese and in taking multivitamins outweigh the risks of developing Parkinson's disease.
He also added that additional studies are necessary to confirm these results.
"Our findings may improve understanding of how Parkinson's disease develops," he said. "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."