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Pesticides May Raise Alzheimer's Risk

Occupational Exposure Linked to Increased Risk of Alzheimer's Disease

By Charlene Laino
WebMD Health News

Reviewed By Louise Chang, MD

July 15, 2009 (Vienna, Austria) -- Exposure to pesticides may have long-term effects on the nervous system, increasing the risk of Alzheimer's disease in late life, a new study suggests.

Researchers say the findings support evidence of a possible link between environmental toxins and Alzheimer's disease and may help explain why some people with risk factors for the disease get it while others do not.

"While no cause for Alzheimer's disease has been found, [non-inherited] cases are likely due to a combination of genetic and environmental factors," says Kathleen M. Hayden, PhD, of Duke University Medical Center in Durham, N.C.

Pesticides and Alzheimer's

Pesticides have been proposed as a possible environmental risk factor, but there are few studies of the effects of occupational pesticides on the risk of Alzheimer's disease, she says.

Research suggests that pesticides may affect the release of acetylcholine, a chemical that's important for memory, Hayden tells WebMD.

Pesticide use has dramatically increased over the past 50 years, she says. There are now more than 18,000 pesticides licensed in the U.S., and more than 2 billion pounds are applied each year, Hayden says.

There are 5.3 million Americans living with Alzheimer's disease, which disrupts memory, learning, and other mental functions. By 2010, there will be nearly half a million new cases each year and by 2050, there will be nearly a million new cases annually, according to the Alzheimer's Association.

Working With Pesticides

The new study involved more than 4,000 residents 65 and older from an agricultural county in Utah who are participating in a larger study of risk factors for Alzheimer's disease.

At the start of study, they were asked if they had ever been exposed to pesticides during their work and if so, which types of pesticide and for how long. Of the total, about 750 participants reported working with pesticides.

A standard test that measures overall cognitive function, including memory, attention span, and problem solving, was given at the outset and two other times over a six- to seven-year period.

The study was presented at the Alzheimer's Association 2009 International Conference on Alzheimer's Disease.

Pesticides Linked to Alzheimer's

After adjusting for age, sex, education, and a gene known to raise the risk of Alzheimer's, the researchers found that people who worked with pesticides were 53% more likely to develop Alzheimer's disease.

The study doesn't prove that pesticides cause Alzheimer's disease, and further research is needed, Hayden says.

The next steps are to look at whether type of pesticide and duration of use affects risk, she says.

Ralph Nixon, MD, PhD, vice chair of the Medical and Scientific Advisory Council at the Alzheimer's Association and an Alzheimer's expert at New York University, tells WebMD that it's been difficult to identify specific toxins that raise Alzheimer's risk.

"You can look at environmental toxins as being something that promotes the root cause of the disease, or as a second hit.

"If someone is already predisposed to Alzheimer's due to genetics, cardiovascular disease, or some other risk factor, the environmental toxin may push their risk over the top," he says.

The American Chemical Society did not offer comment in time for publication. CropLife America, a trade group representing crop protection products and pesticides, could not be reached.

SOURCES: Alzheimer's Association 2009 International Conference on Alzheimer's Disease, Vienna, Austria, July 11-16, 2009. Kathleen M. Hayden, PhD, Duke University Medical Center, Durham, N.C. Ralph Nixon, MD, PhD, vice chairman, Medical and Scientific Advisory Council, Alzheimer's Association; professor of psychiatry and cell biology, New York University.

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