June 9, 2003 -- With apologies to Popeye, there may be a downside to eating too much spinach. New research suggests that people who have high amounts of iron in their diets may be at increased risk of developing Parkinson's disease.
The study compared food and vitamin supplement consumption among Parkinson's patients and subjects of the same age and sex without the disease. The rate of Parkinson's disease was almost double in those with the highest intake of iron and the trace mineral manganese.
But researchers are quick to point out that the health benefits of eating iron-rich foods such as spinach and taking vitamin supplements far outweigh the potential Parkinson's disease risk.
"To put it in perspective, a person's lifetime risk of getting Parkinson's disease is about one in 1,000, so doubling that means the risk would be two in 1,000," University of Washington research scientist Karen M. Powers tells WebMD.
Powers and colleagues found that people who ate diets rich in iron and manganese and also took one or more multivitamins or iron supplements a day had almost double the Parkinson's disease risk compared to those who ate few iron-rich foods and those who took the lowest amounts of vitamin supplements. People who took the highest amounts of both minerals had the highest risk. Their findings are published in the June 10 issue of the journal Neurology.
"A multivitamin is a great addition to a healthy diet, but there were a few people in our study who took more than one vitamin or iron tablet a day on the theory that if one is good, more is better," she says. "We don't know if this contributes to Parkinson's disease, but it isn't recommended."
Parkinson's is known as a complex disease, meaning that in most people it appears to be triggered by a combination of genetic, environmental, and lifestyle factors. The impairment associated with Parkinson's disease is caused by a deficiency in dopamine, the chemical messenger in the nervous system that controls movement. In Parkinson's disease, the cells that make dopamine begin to die off.
Much Parkinson's disease research has focused on the hypothesis that so-called "oxidative stress" is responsible for the death of these dopamine-making cells. Some studies suggest that antioxidants such as vitamin E may protect against Parkinson's, but iron and manganese are known to contribute to oxidative stress.
Parkinson's disease specialist Matthias Kurth, MD, tells WebMD that most Parkinson's disease research these days is focused on finding the genetic causes of the disease. He says the new study may put some of that attention back on the oxidative stress theory.
"This is an important signal that the idea of oxidative stress makes sense as a contributing factor in this disease," he says.