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June 26, 2003

UW studies link iron and manganese intake to Parkinson’s

UW researchers have found that the risk of someone getting Parkinson’s disease after high consumption of both iron and manganese together is greater than expected. Researchers say further studies may shed light on the apparent connection, and they say people should not change their diet on the basis of this study alone.

Other studies have shown that a diet high in iron increases the risk for Parkinson’s disease; the UW study reinforces those findings by demonstrating people in the top 25 percent of iron consumption were 1.7 times more likely to develop Parkinson’s disease than those in the lowest 25 percent.

“What is new about our finding is that the risk for Parkinson’s disease from both iron and manganese together is greater than the risks for each of these two nutrients alone,” said Dr. Karen Powers, a co-author of the paper and a research scientist in the Department of Environmental and Occupational Health Sciences in the UW School of Public Health and Community Medicine.

People who have diets high in both manganese and iron are 1.9 times more likely to be Parkinson’s patients than those who had lower levels of these two nutrients, according to the study. People who have diets high in iron and take one or more multivitamins a day are 2.1 times more likely to develop Parkinson’s disease.

The paper appears in the June 10 issue of Neurology, the journal of the American Academy of Neurology.

Iron and manganese are essential nutrients, and are important in the diet. Powers stressed that researchers are not suggesting that people change their diets on the basis of this study, but they should follow the labeled directions on dietary supplements.

“The benefits of eating foods rich in iron and manganese outweigh the risks of Parkinson’s disease. Foods rich in iron and manganese include spinach, lima beans, peas, wheat bread, peanuts, and other nuts and seeds. Vitamins are also a good supplement to a healthy diet — but ‘more is better’ is not true with all nutrients,” Powers said.

“We had people in this study taking more than one multivitamin a day. That’s not a good idea, regardless. If the directions say ‘take one vitamin a day,’ that really means, ‘take one vitamin a day.’ This is also true for iron supplements.”

She stressed that there is no “easy answer,” or solution, to the question of what causes Parkinson’s. Parkinson’s disease is a complex disorder that has numerous environmental, lifestyle, and genetic factors that determine who will develop the disease.

The research was supported by grants from the National Institute of Environmental Health Sciences. Other authors of the paper include Drs. Harvey Checkoway and Gary Franklin, and Terri Smith-Weller; occupational health nurse, all of the Department of Environmental and Occupational Health Sciences, and Drs. W. T. Longstreth Jr. and Phillip D. Swanson, professors of neurology in the UW School of Medicine.