Q. My dad was recently diagnosed with Parkinson's disease. Could there possibly be an environmental cause?

A. Yes, there could be an environmental factor in Parkinson's disease. A study published in the July 2006 issue of "Annals of Neurology" has found an association between pesticide exposure and Parkinson's disease. According to Dr. Alberto Ascherio, lead author of the study and associate professor of nutrition and epidemiology at the Harvard University School of Public Health, "this is the first large human study that shows that exposure to pesticides is associated with a higher incidence of Parkinson's."

Parkinson's disease is a disorder of the nervous system that causes tremors or involuntary shaking in the limbs and progressive stiffness of the muscles. These symptoms are the result of a loss of brain cells that produce dopamine — a chemical substance that nerves need for body movement and coordination. Parkinson's disease usually affects people older than 50. The disease can cause mild or severe symptoms, and medications can help slow its progression.

The cause of Parkinson's disease is unknown, and there is a lack of strong evidence that genes are solely responsible. For many years, scientists have hypothesized that exposure to pesticides may play a role in its development in susceptible individuals. The recent Harvard study, which found that pesticide exposure could increase long-term risk for Parkinson's disease by as much as 70 percent, further supports this hypothesis.

Although the study did not identify exactly which pesticides the participants were exposed to, an animal study published in "Developmental Neuroscience" (January-February 2004) suggested that pesticides used in agriculture could increase susceptibility to the disease. Earlier studies on animals have shown similar findings, indicating that pesticides can cause damage to the area of the brain that produces dopamine.

What can you do to reduce your risk? You can eat organic food as often as possible, and use a filter in your home for all of your drinking water. If you are unable to buy organic food, be sure to wash all of your produce thoroughly with soap and water. And finally, refrain from using any pesticides in or around your home.

For information on how to treat Parkinson's disease, you can buy your father the book BrainRecovery.com (the author's Web site and the name of his book) by neurologist Dr. David Perlmutter.

Laurie Steelsmith is a naturopathic physician and licensed acupuncturist in Honolulu, and the author of "Natural Choices for Women's Health" (Random House). Reach her and read past columns at www.drsteelsmith .com. This column is for information only. Consult your health provider for medical advice.