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Your Environment. Your Health.

Parkinson's Disease


Elderly woman sitting in a park

Parkinson’s disease (PD) is a progressive neurodegenerative disease and the second most common disorder of this type after Alzheimer’s disease. It progresses slowly as small clusters of dopaminergic neurons in the midbrain die. The gradual loss of these neurons results in reduction of a critical neurotransmitterDictionary of Environmental Health called dopamine, a chemical responsible for transmitting messages to parts of the brain that coordinate muscle movement.

What causes PD?

The exact cause of PD is unknown, though most researchers agree that the disease is caused by both genetic and environmental factors, as well as the interactions among the two.

A full understanding of PD risk requires integrated efforts to study both genetic and environmental factors. If environmental exposures can be identified, it may lead to new targets for prevention and intervention.

What are the symptoms of PD?

Studies have shown that the symptoms of PD usually appear when 50 percent or more of the dopamine neurons in the midbrain have been lost. Symptoms begin gradually and typically worsen over time.

Common motor symptoms include:

  • Tremors or shaking in hands, arms, legs, jaw, and face
  • Rigidity or stiffness of limbs and trunk
  • Slowness of movement
  • Difficulties with balance, speech, and coordination

There are also nonmotor symptoms which may develop years before the onset of motor problems. These may include:

  • Poor sense of smell
  • Constipation
  • Depression
  • Cognitive impairment
  • Fatigue

What are some of the environmental factors researchers believe may be associated with PD?

Pesticides Exposure: Accumulating evidence indicates that pesticide exposure is associated with an increased risk for developing PD. Many animal studies have provided evidence for this, and several human studies are beginning to reveal some specific pesticides and classes of pesticides that may be linked to PD.

Dietary Factors: Both in-house researchers and grantees are continuing to explore the role that diet and lifestyle play in the onset, progression, and treatment of PD. For example, how much fat a person consumes in their diet is one area under study.

Exercise: Research has shown that in a large population of U.S. older adults, higher levels of moderate to vigorous physical activity in midlife were associated with lower risk of PD.

Nicotine: Despite the numerous adverse health effects of cigarette smoking, a large number of studies have consistently found that smokers have a lower incidence of PD than nonsmokers.

Head Injuries: Numerous studies have looked at the role that head injuries may play in PD. This is a reasonable area to explore, since brain injuries involve inflammation, oxidative stress, and possible disruption of the blood-brain barrier, all of which may play a contributing role in neuronal degeneration and PD.

What NIEHS is Doing on Parkinson's Disease 

NIEHS is currently funding more than 30 grants focused on neurodegenerative diseases, including PD. There is also a very strong in-house research community working to understand the role of the environment, genes, and gene-environment interactions in the disease. The multidisciplinary teams of researchers at NIEHS and across the country are working toward ways to prevent PD or slow its progression.

Stories from the Environmental Factor (the official newsletter of NIEHS)

NIEHS Press Releases

NIEHS Research Efforts

General Information 

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