Sep 18, 2026
- Smoking history and exhaled carbon monoxide levels are both associated with a lower risk of developing Parkinson’s disease.
- In a new study, researchers set out to better understand this link. They found that participants who had not smoked but had high exhaled carbon monoxide levels also had lower risk of Parkinson’s disease.
- Having higher exhaled carbon monoxide levels was not linked to a lower risk of other neurodegenerative diseases.
A new study may have shed some light on the peculiar association between smoking and a lower risk of developing Parkinson’s disease.
The study, published in JAMA Neurology, reports that exposure to carbon monoxide may contribute to this link.
Parkinson’s disease is a brain condition that is growing increasingly common. The World Health Organization (WHO) estimates that its prevalence has doubled in the past 25 years.
The disease causes damage to nerve cells in an area of the brain called the substantia nigra, resulting in symptoms such as tremors and coordination problems. Some people with Parkinson’s go on to develop dementia over time.
Experts are unsure what causes Parkinson’s at present, but believe that genetic changes or environmental exposures may play a role.
Previous population studies have noticed a lower risk of Parkinson’s disease among people who smoke.
While studies in rodent models led researchers to suggest that nicotine might have some kind of protective effect, a recent randomized clinical trial found that nicotine therapy provided no benefit to people with Parkinson’s. In fact, the trial suggested the nicotine may have even made their symptoms worse.
Other studies in cells and animals have suggested that carbon monoxide, another by-product of smoking, might also play a protective role.
As a result, an international team of researchers set out to see how carbon monoxide exposure might relate to the risk of Parkinson’s disease.
The researchers examined data from 512,701 participants in the China Kadoorie Biobank, a cohort coming from 10 different urban and rural areas within China. The participants had a mean average of 52 years at the beginning of the study.
Participants provided information about their smoking history along with other aspects of their lifestyle and medical history via questionnaires. Clinicians also measured the amount of carbon monoxide they exhaled.
The researchers examined the health outcomes of the participants over a follow-up period of 12 years. During this time, they noted a total of 1,131 people developing Parkinson’s disease and 2,949 developing other forms of neurodegenerative disease.
They then looked to see if there were any patterns between these health outcomes, smoking histories, and measurements of exhaled carbon monoxide taken at the beginning of the study period.
Sep 17, 2026
September 11, 2026 | Lindsay Ryan Crawford Medically Reviewed by: Clifton Lewis, DO
Key Takeaways
- Parkinson’s disease can cause more than just movement problems.
- Non-motor symptoms can include changes in mood, trouble sleeping, constipation, feeling tired, pain, dizziness, changes in thinking, problems with speech or swallowing and loss of smell.
- Some symptoms may show up years before tremors, stiffness or slower movement begin.
- These symptoms are common, real and often treatable.
- Let your care team know if you notice changes in your sleep, mood, digestion, energy, thinking or daily life.
- The best Parkinson’s care looks at the whole person, not just movement symptoms.
When you think of Parkinson’s disease, you probably think of tremors, stiffness and slow walking.
But Parkinson’s can affect much more than movement, sometimes causing symptoms that people don’t immediately connect with the disease.
“It is so much more than a movement disorder,” says Clifton Lewis, DO, a movement disorder neurologist with Hartford HealthCare Ayer Neuroscience Institute. “Parkinson’s can affect multiple systems throughout the body, which is why symptoms can look very different from person to person.”
Here are nine Parkinson’s symptoms that go beyond movement problems,.
1. Your mood changes
Depression and anxiety are common in Parkinson’s disease.
“And they’re not always just a reaction to the diagnosis,” says Dr. Lewis. “Depression in Parkinson’s can be part of the disease process itself, and that distinction matters.”
Mood changes may include:
- Depression
- Anxiety
- Irritability
- Loss of motivation
- Emotional withdrawal
- Less interest in activities you used to enjoy
“These changes can happen slowly, so they’re easy to miss,” explains Dr. Lewis. “Some people think they’re just stressed, overwhelmed or having trouble adjusting, but it’s more than that.”
2. Sleep gets disrupted
Parkinson’s can affect sleep in different ways. Some people have trouble falling or staying asleep, while others feel very sleepy during the day.
“When sleep is thrown off, patients often notice worsening fatigue, mood and concentration during the day,” says Dr. Lewis.
Sleep issues may include:
- Frequent waking
- Restless or uncomfortable legs
- Excessive daytime sleepiness
- Acting out dreams
- New or worsening fatigue
“One sleep symptom that can be especially surprising is dream enactment behavior,” says Dr. Lewis. “This is when a person may talk, kick, punch or act out dreams while asleep. It can disrupt their sleep and their partner’s, and in some cases, lead to injury. It’s also important to recognize because it can be an early sign of Parkinson’s disease, sometimes appearing years before any obvious movement problems begin.”
Sep 16, 2026
Patients have reduced activity in acetylcholine nerve cell network
Written by Steve Bryson, PhD | Aug. 20, 2026
- Parkinson’s patients experiencing visual hallucinations show reduced activity in the brain’s acetylcholine-using nerve cell network.
- Impaired early cholinergic signaling in specific brain regions can predict which patients will later develop visual hallucinations.
- Measuring cholinergic activity may serve as a biomarker for risk and a target for future therapeutic interventions.
People with Parkinson’s disease who experience visual hallucinations have reduced activity in the brain’s cholinergic system, a network of nerve cells that use the chemical messenger acetylcholine, a brain imaging study found.
Impaired cholinergic signaling in certain brain regions early on predicted who would later develop visual hallucinations.
The researchers said measuring cholinergic activity in certain brain regions could serve as a biomarker to identify patients at a higher risk of developing hallucinations, or as a target for future treatments aimed at reducing or preventing them.
The study, “Cholinergic deficits and hallucinations in Parkinson disease,” was published in npj Parkinson’s Disease.
Sep 15, 2026
Researchers urge monitoring of mental health and metabolic factors
Written by Andrea Lobo | Aug. 21, 2026
- A large study links early depressive symptoms to an increased risk of developing Parkinson’s, particularly for those with high genetic susceptibility.
- Metabolic changes involving fats appear to partly explain the connection between preclinical depression and Parkinson's disease risk.
- Monitoring depressive symptoms and metabolic factors may help identify high-risk individuals for earlier detection, per the researchers.
People with depressive symptoms may have higher odds of developing Parkinson’s disease, a large study suggests, with the researchers noting a potentially greater risk among those with stronger genetic susceptibility to the neurological condition.
The findings also point to changes in fat metabolism — one of several “metabolic disturbances” that the team says has been “independently associated with both depressive symptoms and [the development of Parkinson’s]” — as a possible link between the disease and these signs of depression. The researchers noted that “genetic factors also play a well-established role in [Parkinson’s] susceptibility.”
Overall, the study “demonstrates that even subthreshold depressive symptoms … are associated with a higher risk” of Parkinson’s, the researchers wrote. Still, the team noted that they could not definitively determine whether depression is a true independent risk factor for Parkinson’s or an early manifestation of the disease.
“Our results extend previous evidence linking clinical depression with [Parkinson’s] risk by focusing on preclinical depressive symptoms, which are more prevalent in the general population yet have been less studied in relation to [Parkinson’s],” the researchers wrote.
The study, “Association of pre-clinical depressive symptoms and its plasma metabolomic signature with Parkinson’s disease: a community-based longitudinal study,” was published in the journal Translational Psychiatry.
A progressive disease, Parkinson’s is caused by the loss of dopaminergic neurons, which are the nerve cells that produce dopamine, a brain signaling molecule involved in movement. In addition to its hallmark motor symptom of tremor, people with Parkinson’s may experience nonmotor symptoms, including mental health problems such as depression.
36% higher risk of Parkinson’s found with depressive disorders
Previous studies have also suggested that people diagnosed with depression may have a higher risk of developing Parkinson’s. However, it is less clear whether milder depressive symptoms preceding a formal diagnosis of depression may also be an early sign or risk factor for Parkinson’s.
In this study, researchers in China and Sweden aimed to clarify the extent to which depressive symptoms increase the risk of Parkinson’s development and whether this association varies according to genetic predisposition for the disease.
For that, they analyzed data from 451,922 people without Parkinson’s taking part in the UK Biobank, a large-scale biomedical database. Among the participants, 5.9% had a possible depressive disorder. That was defined as a score of three or higher on the two-item Patient Health Questionnaire, used by healthcare workers to screen and track the severity of mental health conditions such as depression and anxiety.
Those with possible depression were more likely to be younger, female, and of non-white race, the data showed. The researchers noted these individuals more frequently had less education, more irregular physical activity, and less sleep duration. They also were more likely to have other conditions such as diabetes, cardiovascular diseases, and a previous history of depression.
During a median follow-up of 14.6 years, 3,108 participants (0.7%) developed Parkinson’s: 194 who had possible depression and 2,914 who did not.
After adjusting for multiple factors, analyses showed that individuals with a possible depressive disorder had a 36% higher risk of developing Parkinson’s than those without.
Sep 14, 2026
Delaying rehab raised mortality risk regardless of disability level
Written by Andrea Lobo | Aug. 24, 2026
- Parkinson's disease involves the progressive loss of dopamine-producing neurons, leading to motor symptoms.
- Starting rehabilitation within the first year of a Parkinson's diagnosis may be linked to longer survival.
- Delaying rehabilitation is associated with a progressively higher risk of mortality across all disability levels.
Starting rehabilitation within the first year after a Parkinson’s disease diagnosis may be associated with longer survival, even among people who had already developed disability, a nationwide South Korean study found.
Delaying rehabilitation was associated with progressively higher mortality risk across all disability levels, including among people without functional impairment.
Researchers said these findings “indicate that the survival benefit of timely rehabilitation is not confined to the pre-disability stage; even among individuals with functional impairment, the prompt initiation of rehabilitation therapy remains meaningfully associated with improved long-term outcomes.”
The study, “Timing of rehabilitation therapy initiation and all-cause mortality in parkinson’s disease: nationwide cohort study,” was published npj parkinson’s disease.
Rehabilitation an important part of long-term Parkinson’s care
Parkinson’s is caused by the progressive loss of dopaminergic neurons, nerve cells that produce dopamine, a signaling molecule involved in movement. This leads to motor symptoms, such as tremors, slow movements, and balance and gait problems.
While medications can ease symptoms, they do not stop the disease from progressing, making rehabilitation an important part of long-term care. Guidelines recommend starting rehabilitation early, although in practice this is often delayed until people develop walking or balance problems. Whether starting rehabilitation early can affect patients’ long-term outcomes, including survival, remains unclear.
To learn more, researchers in South Korea used national health insurance data to examine whether the timing of rehabilitation after a Parkinson’s diagnosis was associated with the risk of death, and whether this association differed according to disability severity.
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