Urban Exposure to Manganese, Copper May Raise Parkinson's Risks


NPF's National Medical Director, Dr. Michael S. Okun, comments on new research indicating that manganese and copper may raise Parkinson's disease risk. Read the full story from Medscape Today below. 

Urban Exposure to Manganese, Copper May Raise Parkinson's Risks

Being exposed to high levels of manganese or copper in urban areas could increase risks of developing Parkinson's disease (PD), according to the results of a new study.

Previous studies found that exposure to pesticides in rural areas may be an environmental trigger for PD, but this new research looked at a different kind of exposure in more densely populated areas.

"Our study was the first to look at environmental risk factors in urban areas, and this data suggests that perhaps manganese and copper emissions may be some of the triggers for susceptible individuals," said lead study author, Allison W. Willis, assistant professor of neurology at Washington University School of Medicine, St. Louis, Missouri.

The study was published online October 19 in the American Journal of Epidemiology.

Researchers used data from the Toxic Release Inventory of the Environmental Protection Agency, which contains detailed information on chemical releases and waste management activities. They extracted data on onsite metal releases at US facilities for copper, lead, and manganese from 1988 to 1998 and calculated cumulative data per county for this 10-year period.

Urban PD Cases

Investigators also accessed data, including date of birth, race, sex, county, and zip code of residence for neurologist-diagnosed PD patients. Only those beneficiaries who had been enrolled in Medicare since 1995 and resided in the same county at that time were included in the study. As well, only residents of urban areas — defined as metropolises of more than 250,000 people — were included.

During the study period, more than 35,000 PD cases met inclusion criteria in 1046 counties across the United States. For each case, researchers ended the exposure period 5 years before incident diagnosis to allow for latency in symptom onset and seeking medical attention.

Twenty-six industries had reportable copper, manganese, or lead release. The mean reported onsite metal release during the study period was 3.18 metric tons per year for copper, 1.22 metric tons per year for lead, and 1.90 metric tons per year for manganese.

The incidence of PD was elevated in counties with high reported manganese release at 489.4 cases per 100,000 vs 274 cases in counties with no or low release of copper, lead, or manganese (relative risk [RR], 1.78; 95% confidence interval [CI], 1.54 - 2.07). In counties with high copper release, the PD incidence was 304.2 per 100,000, also a relative increase in risk (RR, 1.1; 95% CI, 0.94 - 1.31).

Lead Sources

The study did not find a very strong correlation between industrial lead output and the incidence of PD (RR, 1.04; 95% CI, 0.88 - 1.23). "However, what that may mean is that the increased risk of Parkinson's disease associated with lead that has been found in other good studies may be due to other sources," said Dr. Willis. "We looked at industrial release, but the risk associated with lead may be coming from lead paint, lead in the water, or other sources."

Previous laboratory research has shown that copper, manganese, and lead all cause changes in tissue similar to those seen in PD. As well, some observational studies have found that some people exposed to these metals in their occupation developed clinical syndromes similar to PD.

Combined, this research suggests that these metals may have a neurotoxic effect in the same area of the brain affected in PD, said Dr. Willis. "These metals may interfere with the brain's ability to rid itself of toxic radicals. They may also be able to induce or accelerate the formation of clumps of protein found in people who have neurodegeneration."

What exactly these metals are doing to the brain to make it more susceptible to PD is a subject of active research at Washington University, said Dr. Willis. "We're looking at what changes may be occurring in the brain both before death and after death in people exposed to metals."

Not a Small Town Problem

In this current study, researchers found little variation among study regions in terms of education, income, and property values. "We have this picture of the kind of the neighborhood with high pollution rates of manganese, copper, and lead being a small factory town, and that's not the case," said Dr. Willis. "There are neighborhoods with million dollar houses that are right down the street from one of these emitting facilities."

The new information might suggest that research should concentrate on overall metal pollution levels rather than focusing on any particular industry, said Dr. Willis. Manganese, copper, and lead are used in a number of different industries, from clothing, concrete, and cement manufacturing to tobacco refining.

Focusing on one or only a few industries may explain conflicting results of previous studies, she added.

Pollution Protection

Future studies may investigate whether inherited characteristics may offer protection against various pollutants. "That's a study we're getting ready to start now," said Dr. Willis. "It's been well shown that certain races and the female gender are somewhat protected against Parkinson's disease." African Americans and Asian Americans have a rate of PD that's about half that of whites, she noted.

"I think we'll end up finding that just like heart disease or diabetes, many of us are born with a genetic susceptibility," said Dr. Willis. "If diabetes runs in my family, I may be at risk of getting it, but if I exercise and am not overweight then I won't. Similarly, many of us may be born with a genetic susceptibility for Parkinson's disease, and we are now identifying environmental triggers."

Genetics accounts for about 15% of PD cases, she said.

Asked to comment on this new research, Michael S. Okun, MD, national medical director of the National Parkinson Foundation, pointed out, "It has long been held by experts that genetics loads the gun, and the environment pulls the trigger."

This new study "reinforces the notion that the environment may play an important role in the development of Parkinson's disease," said Dr. Okun in an email to Medscape Medical News. "This is an area that many National Parkinson Foundation investigators have been actively pursuing, and trying to better understand."

-- Pauline Anderson

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