What are the risk factors for Parkinson's disease?

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In most people with Parkinson’s disease, symptoms become noticeable at the age of 60 years or above.

However, in 5–10% of cases, they appear earlier. When symptoms develop before the age of 50 years, a person has what is known as early onset Parkinson’s disease.

Males appear to have a 50% higher risk of developing Parkinson’s disease than females.

However, at least one study has found that as females get older, their risk of developing it increases. Researchers have suggested that this could be due to a variety of factors, including:

• lifestyle factors
• genetic features
• hormonal and reproductive factors
• differences in the brain structures that relate to the production of dopamine

According to the Parkinson’s Foundation, around 10–15% of cases may be due to genetic factors. However, the National Institute on Aging notes that, in most cases, the condition does not seem to run in families.

Experts have identified several genes in which changes may result in Parkinson’s disease, but these are not necessarily hereditary.

Some genes affect the risk of developing Parkinson’s disease, but they do not cause symptoms. The gene known as GBA is one of these. This gene makes the enzyme glucocerebrosidase.

As scientists learn more about how genetic factors link to Parkinson’s disease, it may become easier to predict who is most likely to develop symptoms. This could lead to earlier intervention and possibly more effective treatments.

Genetic testing

Not everyone with a gene mutation will develop Parkinson’s disease. Some people with a family history of the condition choose to undergo genetic testing to have some idea of how likely they are to develop it. This can help people understand the condition and enable them to plan for it.

However, there are also arguments against testing. Some people have a genetic factor but never develop the condition. This can lead to unnecessary anxiety. Others argue that testing is not worth it, as it does not change the outcome.

Therefore, experts urge people to think carefully before deciding to have a test. Home tests are available, but it is best to start by seeking the advice of a healthcare professional.

There has been little investigation into how Parkinson’s disease affects people of different races. Some research has suggested that it affects specific groups differently in the United States, with higher rates among white people and fewer diagnoses among Black Americans.

However, these figures may be misleading. One explanation may be that Black people are less likely to receive an early or accurate diagnosis.

A 2020 review highlights the lack of information about how Parkinson’s disease affects different populations, noting that racism and health inequity have played a role in this.

Experts have called for more equitable research into how Parkinson’s disease affects specific groups. This could improve the recognition of the symptoms and improve levels of care.

People who sustain a blow to the head on at least one occasion may have a higher risk of developing Parkinson’s disease.

A 2018 study found that, among military veterans, even a mild traumatic brain injury could increase the risk of Parkinson’s disease by 56% — even after the researchers had accounted for psychological and other factors.

This has raised concerns among athletes, as concussion is a common injury in football and many other activities.

People who participate in sports that tend to cause head injuries should wear protective headgear and seek medical help if they experience a blow to the head.

Also, everyone should use a safety belt or other age-appropriate restraint when traveling in a vehicle.

There is some evidence to suggest that exposure to some drugs and toxins may increase the risk of Parkinson’s disease.

Herbicides and pesticides

Exposure to certain toxins can affect the brain cells that produce dopamine, according to some scientists. This may increase the risk of Parkinson’s disease.

Substances that may have this effect include:

• organochlorines, which are now banned in the U.S. but have previously been used in insecticides, such as chlorpyrifos
• organophosphates, which are present in many household products
• pyrethroids, which are used in insecticides and mosquito repellants

Specific products that may increase the risk include paraquat and rotenone.

Research has found links between Parkinson’s disease and the herbicide paraquat. According to the Parkinson’s Foundation, paraquat is widely used in the U.S. but banned in many other countries. The Parkinson’s Foundation has been lobbying to ban its use.

Exposure to the phytochemical rotenone, which people use to kill fish in reservoirs, may also pose a risk.

Some veterans who fought in the Vietnam war appear to have a higher risk of developing Parkinson’s disease. Scientists have suggested that exposure to dioxin, which is present in the defoliant Agent Orange, may have played a role.

Studies have also found higher rates of Parkinson’s disease among people who work as farmers, those exposed to well water, and those who live in rural areas.

Although much of the evidence has been observational, one 2017 review found a significant link between the use of some pesticides and genetic changes that can underlie Parkinson’s disease. The authors called for more research to identify the exact link.

Metals

Some researchers have noted a possible link between long-term exposure to certain metals and a higher risk of Parkinson’s disease.

These metals include:

• mercury
• lead
• manganese
• copper
• iron
• aluminum
• bismuth
• thallium
• zinc

People who work in environments where exposure is common may have a higher risk. However, the risk is difficult to measure, and there is no evidence to confirm what role any of these metals might play in the development of Parkinson’s disease.

Solvents

Many industries use the solvent trichloroethylene (TCE), and it is commonly present in groundwater. People who experience long-term exposure to TCE may be more likely to develop Parkinson’s disease later in life.

Some experts have suggested that exposure to TCE and another solvent, called perchloroethylene, may have contributed to higher rates of Parkinson’s disease among veterans of the Vietnam war. These solvents were present in the water supply at Camp Lejeune.

Polychlorinated biphenyls

Some scientists have found higher levels of polychlorinated biphenyls (PCBs) in the bodies of people with Parkinson’s disease, suggesting that PCB exposure may increase the risk of this condition.

However, other studies have not confirmed this.

Some medications, such as antipsychotics for treating severe paranoia and schizophrenia, may cause Parkinson’s-like symptoms known collectively as Parkinsonism. This is because they block the action of dopamine.

Synthetic heroin

There is evidence to suggest that using MPTP, which is a synthetic heroin product, can lead to Parkinson’s-like symptoms.

In 2018, a group of scientists published case notes on seven young adults who had used the drug. The individuals showed symptoms of Parkinsonism after short-term use of the drug.

The researchers did not conclude that the people developed Parkinson’s disease, but their symptoms suggested that their bodies had undergone similar processes.

People who have exposure to nicotine may have a lower risk of developing Parkinson’s disease, according to one 2017 study.

This does not mean that people should smoke to prevent Parkinson’s disease, as the hazards of smoking would far outweigh any benefits.

However, it does suggest that nicotine could play a role in future treatments.

The Parkinson’s Foundation notes that people who do any of the following may have a lower risk of developing the condition:

• drinking coffee or tea containing caffeine
• having high levels of uric acid in the blood, though this can also lead to gout
• using anti-inflammatory drugs, such as ibuprofen
• using statins to reduce cholesterol levels
• having a higher level of vitamin D
• exercising regularly from early life

One 2020 study noted that the risk of developing Parkinson’s disease among people with type 2 diabetes appeared to vary according to their treatment. Rates of Parkinson’s disease were lower among people using DPP4 inhibitors, GLP-1 receptor agonists, or both, suggesting a possible protective factor.

A person should speak with a healthcare professional before making any significant lifestyle changes, as some of these practices may introduce hazards or risks of their own.

Can diet help people with Parkinson’s disease?

A 2018 review concluded that exercise could play a preventive role. It may also help treat the symptoms and slow the progression of the condition, especially in the early stages.

Anyone with a diagnosis of Parkinson’s disease should speak with a healthcare professional about a suitable exercise plan.

Genetic features may play a role in some cases of Parkinson’s disease. For most people, however, it is not possible to identify a cause.

Some studies have suggested that exposure to certain toxins, including a number of herbicides and pesticides, may increase the risk.

Several factors, including exercise, may reduce the risk. Overall, however, there is no evidence to suggest that any specific action can prevent Parkinson’s disease.