Parkinson’s disease occurs in about 2 percent of the general population; it is the 14th leading cause of death, according to the Centers for Disease Control and Prevention. How Parkinson’s develops isn’t fully understood, but it is known that several agricultural fungicides, fumigants, herbicides and insecticides increase its occurrence.

Adding to the conundrum is that Parkinson’s has many contributing factors that precipitate and worsen the disease, such as our genetic makeup. To sort out the understanding of Parkinson’s, and because it is mostly outside my expertise, I examined numerous scientific studies and consulted two medical doctors.

A retired farm couple who aren’t clients taught me much about the personal toll of Parkinson’s. “Kathy” worked off the farm in office positions for 45 years besides helping her husband, “Bob.” Ten months after Kathy retired, her physical movements slowed considerably.

She suspected what was happening; medical tests confirmed Parkinson’s. Two years later, Bob quit farming to assist her.

Mostly everyone who learned about Kathy’s illness felt she was cheated during her retirement years, but not Kathy and Bob. Now nine years later, Kathy is wheelchair-bound, requires much help with daily living and types on a computer because her spoken words are difficult to discern. They still live in their modified farm home.

Kathy and Bob don’t complain. They inspired this column; I am grateful for their example to the rest of us who struggle with accepting “not my will, but Thine.”

What are possible indications of Parkinson’s? Early signs are usually mild and vary; sometimes we ignore them. Parkinson’s symptoms may include:

•A tremor in a hand or limb, even when relaxed, but which by itself is insufficient for diagnosis of Parkinson’s

•Slowed and rigid movements that make tasks more difficult to complete

•When walking, steps may become shorter and affected people often shuffle

•Muscles may become stiff, along with limitations of range of motion, posture and balance

•Autonomic movements such as smiling may decrease, making people with Parkinson’s appear emotionally flat, but they usually know and feel “everything”

•Speech often changes, with softer, slurred and monotone words, but not most thinking until the latter stages

•Writing legibly becomes difficult and people often compensate with smaller penmanship

Although onset of Parkinson’s is usually after age 60, it can occur as early as 29 years of age, as it did to the actor Michael J. Fox. It’s a neurological disorder with movement impairments and other symptoms, but without headaches, that worsens gradually.

There are many other causes of movement disorders, such as trembling hands, so those suspecting Parkinson’s should not conclude such without medical confirmation.

What causes Parkinson’s? The disease disrupts and eventually incapacitates the brain cells of the basal ganglia (brain stem), which controls important functions, such as voluntary movements and connections with other parts of the brain.

Brain cells in the basal ganglia increasingly become compromised and develop protein masses called Lewy bodies, which render them unable to perform normally. These brain cells cannot produce sufficient dopamine, an essential transmitter chemical in the nervous system.

Research evidence suggests a genetic proclivity within families for the disease. Genetic testing is available for proneness to some – but not all – Parkinsonian conditions.

How do agricultural pesticides enhance Parkinson’s? Several major studies – such as the ongoing longitudinal Agricultural Health Study of farm chemical applicators in North Carolina and Iowa, and two fairly recent (2002 and 2006) meta-analyses of many scientific investigations, which I reviewed – indicated that accumulated exposures to several agricultural fumigants, fungicides, herbicides and insecticides are associated with the development of Parkinson’s disease.

According to a February 2007 article in the American Journal of Epidemiology and an April 2014 article in Scientific American, the herbicide paraquat and the insecticide and fish toxin rotenone were most strongly linked in a statistical fashion as contributing factors to Parkinson’s.

Several fungicides and fumigants also were more weakly, but positively, linked statistically with the development of Parkinson’s: maneb, ziram, benomyl, triflumizole, captan and folpet. The banned insecticide dieldrin also was associated with the development of Parkinson’s disease.

Much more research is needed, however, to clarify how these substances, other pesticides and other factors contribute to Parkinson’s. Bob isn’t sure if the herbicides and insecticides he used on their farm contributed to his wife’s Parkinson’s; he wonders about this much, he said.

Can we prevent or reduce the onset of Parkinson’s? Thus far, the disease cannot be cured, but several factors are implicated in the onset of Parkinson’s:

•Consuming caffeine in coffee or green tea is a known preventative

•Men are more likely to develop Parkinson’s disease than women

•Exercise, consumption of foods high in antioxidants and Coenzyme Q10 may help prevent onset

•Avoid head trauma (think Muhammad Ali, brain-injured soldiers and sports players with traumatic brain injuries)

•Carefully handle all farm pesticides with personal protective equipment

I thank Kathy and Bob and the physicians who helped me with this column. There is so much more to learn about Parkinson’s.

The views and opinions expressed in this column are those of the author and not necessarily those of Farm World. Dr. Mike Rosmann is a psychologist and farmer in western Iowa. Readers may contact him at mike@agbehavioralhealth.com