Causes and Risk Factors of Parkinson’s Disease

Elderly woman suffering from neck pain

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Parkinson’s disease is a neurodegenerative condition, which means it affects the function of the brain and nervous system

Your nerves carry messages and information from your brain and spinal cord to your muscles and organs, coordinating your movements and bodily functions. As Parkinson’s disease progresses, it causes nervous system function to decline, making movement and bodily functions difficult.

The exact causes of Parkinson’s disease are still unclear. However, research has identified several physical, genetic, and environmental factors that can contribute to the neurodegeneration associated with this condition.

Age is a major risk factor for Parkinson’s disease, as it often starts around the age of 60. Early-onset Parkinson’s, which is often genetic and affects around 5% to 10% of people with the condition, starts before the age of 50. 

Brain & Body Risk Factors

Parkinson’s disease is marked by lower levels of chemicals messengers, or neurotransmitters, which are responsible for the symptoms of this condition. Additionally, people with Parksinson’s may have unusual clumps of protein deposits in their brain, known as Lewy bodies.

Reduced Dopamine Levels

The neurodegeneration that characterizes Parkinson’s disease starts in the brain, in an area known as the substantia nigra, located in the middle of the brain. Small clusters of nerve cells, or neurons, in this area stop functioning properly and die. 

The neurons in the substantia nigra normally produce an important neurotransmitter known as dopamine. Dopamine is responsible for transmitting signals to parts of your brain that control your muscles and ensure smooth and coordinated movements.

The loss of neurons in the substantia nigra leads to low dopamine levels in your brain. This weakens communication between your brain and your muscles and affects your movements. As a result, the primary symptoms of Parkinson’s disease are typically muscle and movement-related issues, such as tremors in your limbs, slow movements, and muscle rigidity.

Symptoms typically start appearing when approximately 50% of the dopamine neurons are depleted. As more neurons are lost, the condition gets progressively worse, until the brain is unable to control movement at all.

Parkinson’s disease is therefore classified as a movement disorder and primarily treated with dopamine therapy.

Reduced Norepinephrine Levels

Parkinson’s disease is also typified by low levels of another neurotransmitter, known as norepinephrine. This happens due to a loss of nerve endings that produce this chemical. 

Norepinephrine plays an important role in the sympathetic nervous system; it is the primary chemical messenger for this system. This system is responsible for several autonomic body functions, such as digestion, blood pressure, heart rate, and even breathing.

Low norepinephrine levels are the cause of the non-movement-related symptoms of Parkinson’s disease. These can include fatigue, slower digestion, and a sudden drop in blood pressure upon standing from a seated or lying-down position.

Accumulated Lewy Bodies

People with Parkinson’s disease may have substances in their brain cells known as Lewy bodies, which are unusual clumps of a protein called alpha-synuclein. This protein is clumped in a way that can’t be broken down. 

Lewy bodies are microscopic markers of Parkinson’s disease. People with the symptoms of Parkinson’s disease who don’t have Lewy bodies in their brain are sometimes diagnosed with parkinsonism. Parkinsonism is an umbrella term for the movement-related symptoms of Parkinson’s disease, stemming from various causes.

Lewy bodies and alpha-synuclein are a major area of focus for researchers of Parkinson’s disease. People with Parkinson’s disease also tend to have abnormal clumps of misshapen alpha-synuclein proteins in their intestines, suggesting that there may be a connection between Parkinson’s disease and gut health.

Family History & Genetics

Researchers have been able to identify certain genetic mutations that can increase the risk of developing Parkinson’s disease. 

These are the two types of Parkinson’s disease, from a genetic standpoint:

  • Hereditary Parkinson’s disease: Roughly 15% of all cases of Parkinson’s disease are inherited. In these cases, mutations in certain genes are passed down through families and increase the individual’s risk of developing this condition. 
  • Sporadic Parkinson’s disease: On the other hand, cases in which people don’t have a family history of Parkinson’s disease are referred to as sporadic cases. These cases are in fact the majority. Scientists have found that alterations in certain genes may also play a role in sporadic cases, in addition to other environmental and lifestyle-related factors.

However, the role that these genetic mutations play in the development of the condition hasn’t been fully understood yet. 

Lifestyle Risk Factors

Apart from genetic factors, certain environmental and lifestyle-related factors may also increase your chances of developing Parkinson’s disease and contribute to the progression of the condition:

  • Vitamin D deficiency, as this nutrient plays an important role in maintaining brain health. 
  • Meat cooked at high temperatures, which can release cancerous compounds that may also cause Parkinson’s.
  • Exposure to air pollution may cause inflammation in the brain and trigger the accumulation of alpha-synuclein deposits in the brain, sometimes from childhood.
  • Exposure to pesticides can cause several biological reactions in the brain that lead to the damage and death of dopamine-producing neurons.
  • Exposure to trichloroethylene (TCE), a chemical compound used in some household cleaning products, dry cleaning, and industrial degreasing. Industrial sites may release this compound into the environment.
  • Exposure to heavy metals such as manganese in industrial settings; the greater the exposure, the greater the chances of developing symptoms associated with Parkinson’s disease.
  • Head injuries, which can contribute to the loss of dopamine, especially in people who have been exposed to pesticides.

On the plus side, caffeine intake may help reduce your risk of developing Parkinson’s disease.

4 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Kim S, Kwon S-H, Kam T-I, et al. Transneuronal propagation of pathologic α-synuclein from the gut to the brain models parkinson’s disease. Neuron. 2019;103(4):627-641.e7. doi:10.1016/j.neuron.2019.05.035

  2. Fullard ME, Duda JE. A review of the relationship between vitamin d and parkinson disease symptoms. Front Neurol. 2020;11:454. doi:10.3389/fneur.2020.00454

  3. Shin S, Burnett RT, Kwong JC, et al. Effects of ambient air pollution on incident Parkinson’s disease in Ontario, 2001 to 2013: a population-based cohort study. Int J Epidemiol. 2018;47(6):2038-2048. doi:10.1093/ije/dyy172

  4. Agim ZS, Cannon JR. Dietary factors in the etiology of parkinson’s disease. Biomed Res Int. 2015;2015:672838. doi:10.1155/2015/672838

Additional Reading

By Sanjana Gupta
Sanjana is a health writer and editor. Her work spans various health-related topics, including mental health, fitness, nutrition, and wellness.