Manganese tied to higher rates of Parkinson's disease.

Nov 29, 2010

Willis, AW, BA Evanoff, M Lian, A Galarza, A Wegrzyn, A Schootman and BA Racette. 2010. Metal emissions and urban incident Parkinson disease: a community health study of Medicare beneficiaries by using geographic information systems. American Journal of Epidemiology http://dx.doi.org/10.1093/aje/kwq303.



Synopsis by Patrick H. Ryan and Wendy Hessler

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A recent study finds that Medicare recipients who live in urban areas with high levels of manganese emissions are about 75 percent more likely to develop Parkinson's disease compared to those in urban areas with lower manganese emissions. Though the causes of Parkinson's disease are not established with certainty, prior studies suggest exposure to environmental toxicants – particularly metals and pesticides – may play a role in the development of the disease.

 
 
 

Context

Parkinson's’s disease is a progressive disorder of the nervous system that affects motor skills and cognitive processes. It generally afflicts people older than 40 and worsens with age.

The symptoms of Parkinson's disease vary from person to person but frequently include tremor, a reduced ability to make voluntary and automatic movements, and impaired posture and balance. Speech and hearing can also be affected.

Doctors and scientists do not know what causes the cell death in the brain that leads to Parkinson's disease. A combination of genetics and environmental factors likely play a role. Many researchers suspect that exposure to certain environmental toxicants causes the majority of cases. For example, pesticide exposures or living near farmland are environmental factors that are linked to the disease.

Manganese is an element that is needed in small amounts to keep people healthy. Food and water supply the trace quantities needed. At higher levels, it is poisonous. Dangerous exposures can occur in the workplace when manganese-laden dust is breathed. Manganese is important in the manufacture of stainless steel and aluminum alloys and is used as a pigment and in batteries. 

Exposure to metals like copper, lead and manganese can induce similar symptoms as Parkinson's disease. Studies show all three can affect the brain nerve pathways associated with Parkinson's onset and progression.

Whether these metals can cause the disease itself is not known. Previous surveys have found high levels of Parkinson's disease among Medicare recipients who live in urban areas in the Midwest and Eastern United States. These areas also happen to be where the most steel, aluminum and other factories that emit maganese and the other metals are located.

What did they do?

Scientists from Washington University in St. Louis examined the incidence of new cases of Parkinson's disease between 1993 and 2005 among Medicare recipients – in four age groups between 70 and more than 85 years old – who lived in 1,046 U.S. urban counties. These were defined as counties with more than 250,000 people. 

The researchers gathered metals emissions data from the U.S. Environmental Protection Agency's Toxic Release Inventory. They determined the pounds of copper, lead and manganese that were released into the air from factories and other facilities in each urban county between 1988 and 1998. Counties with levels of metal emissions higher than 75 percent of all the other counties were considered highly exposed counties. Those counties with emissions less than 75 percent of all the other counties were considered low exposed counties.

The rate of new Parkinson's disease cases in each highly exposed urban county – adjusting for age, race and gender – was compared to the rate of new cases of Parkinson's disease in lower exposed urban counties. Those with no Medicare claims for Parkinson's disease for the prior two years yet who were diagnosed with the disease by a neurologist were considered new cases.

What did they find?

More than 35,000 cases of Parkinson's disease were included in the study.

Almost every state reported the number of pounds of the three metals released during the study period. Alaska reported only lead releases.

The rate of Parkinson's disease was about 75 percent higher in urban counties with high emissions of manganese compared to counties with lower emissions of manganese.

The rate of new cases of Parkinson's disease was higher in counties with high copper emissions. This finding, though, was not statistically solid and could also be due to chance.

The rate of Parkinson's disease in urban counties with high emissions of lead was not significantly higher than the rates in urban counties with low emissions of lead and copper.

What does it mean?

Passive environmental exposure to metals – especially manganese – may be a risk factor for developing Parkinson's disease.

Overall, more long-term residents had Parkinson's disease in counties that reported high releases of all three of the metals – lead, copper and manganese – as compared to the counties with no or lower level releases. Significantly more cases of Parkinson's disease were seen in urban counties with high manganese emission when compared with rates in lower exposed counties.

This study is among the first to show increased Parkinson's disease rates across the United States among those who live in urban counties with high manganese emissions. The study looked at a specific, large population: Medicare recipients. Previous studies of workers exposed to metals like lead, copper and manganese show they can cause symptoms of Parkinson's disease, but not the disease itself. The exclusion of nonurban counties also makes it unlikely that pesticide exposure is responsible for the effects seen.

Though this research suggests that manganese is a risk factor for developing Parkinson's disease, it has some limitations. One is the lack of individual exposure levels to lead, copper and manganese for each Medicare recipient. The lack of personal exposure data means that other factors associated with living in areas with high manganese exposure may be responsible for the increased rates of Parkinson's disease.

Despite the limitations, the results of this study add to an increasing body of research that implicates environmental exposures – particularly metals and pesticides – in developing Parkson's disease.


Resources

Manganese. Micronutrient Information Center. Linus Pauling Insitute, Oregon State University.

Manganese. ToxFAQs, Agency for Toxic Substances and Disease Registry.

Parkinson's Disease. MedlinePlus, U.S. National Library of Medicine and National Institutes of Health. 

 

 

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