For many scientists working in Parkinson’s research, the global rise in the number of people being diagnosed with the degenerative brain disease has become impossible to ignore. It is now the fastest-growing neurological disorder, with studies suggesting cases could double from six million to more than 12million by 2040.
In the UK there are 166,000 people living with the incurable disease – up from 120,000 in 2010, a rise of 38 per cent in 15 years. The real figure is likely to be higher because there is still a backlog of patients who were not diagnosed during Covid.
Largely a disease of ageing, it develops mainly in people over 60 when brain cells die and stop producing an essential chemical called dopamine, which controls movement. This triggers symptoms such as tremors and stiffness, alongside depression, sleep problems and difficulties with focus, memory and decision-making. A big part of this global rise – including in the UK – is because more people are living long enough to be diagnosed with it. But age is not the only driver.
Some experts in the US, who point to increases in diagnoses even in younger adults, describe the rise in Parkinson’s as a ‘man-made pandemic’, driven by exposure to industrial chemicals and pesticides. Other studies point to air pollution and the potential role of viruses – including flu, herpes and hepatitis C – in triggering processes in the brain that ultimately lead to the disease.
What causes any disease in an individual is extremely difficult to pinpoint, and Parkinson’s is no different. But these environmental factors are being closely studied to assess how much of an effect they might be having.
As Claire Bale, at Parkinson’s UK, says: ‘We think it is a combination of your genes with environmental factors, lifestyle and the process of ageing, and it’s hard to untangle. We don’t think our DNA is changing. So is there something external driving an increase? That might be true in some places.’
Professor Miratul Muqit, director of the UK Dementia Research Institute Parkinson’s Research Centre, adds: ‘I think it’s fair to say that, globally, there has been an increase in Parkinson’s cases which goes beyond an ageing population – but it’s not underpinned by a rigorous analysis. More people are being diagnosed, but no one has proven that the increase could be linked to factors outside of ageing.
Some experts in the US describe the rise in Parkinson’s as a ‘man-made pandemic’, driven by exposure to industrial chemicals and pesticides
There is also emerging research on the effect of air pollution on the brain. Traffic fumes and smoke from woodburners contain toxic particulates called PM2.5, which are so small they can be inhaled deep into the lungs
‘However, I’m receptive to the idea there are contributions from our exposure to the environment.’ One factor receiving significant attention in research is pesticides, particularly those used in agriculture.
Studies from the US show people most exposed to agricultural pesticides such as paraquat and rotenone are 2.5 times more at risk of developing Parkinson’s.
Laboratory studies on those used in the US indicate some can poison the ‘battery packs’ in brain cells, known as mitochondria. These then leach toxins that cause a protein called alpha-synuclein – a hallmark of Parkinson’s disease – to build up. This, in turn, triggers brain cells to die and stops the release of dopamine, causing the motor symptoms of the disease. While these chemicals continue to be used in the US, all have been banned in the UK for many years – in the case of rotenone and paraquat, for two decades.
But what isn’t clear, Prof Muqit says, is whether the ‘new generation’ of pesticides that replaced them in the UK have completely eliminated the Parkinson’s risk.
As Tilo Kunath, professor of regenerative neurobiology at the University of Edinburgh, points out: ‘Banning these pesticides hasn’t led to any decrease in Parkinson’s incidence – suggesting there could be others in use which are causing the same issues. It also takes decades between exposure and the disease emerging.’
Sarah Frow was just 44 when she was diagnosed with early-onset Parkinson’s in 2021, following three years of niggling symptoms that she had put down to stress or exhaustion.
The mother of two, from Tenterden, Kent, first noticed a tremor in her left hand before two of her fingers began curling involuntarily into a claw-like position. Her arm and one leg became heavier and less responsive, while she noticed subtle changes to her balance and co-ordination.
She was diagnosed after seeking a private neurology consultation, when NHS tests, following a seizure, proved inconclusive.
‘The doctor said he thought it was Parkinson’s disease,’ says Sarah, now 49.
‘I remember thinking he must be wrong. I thought I was far too young. But then I was angry and upset. I kept thinking, “Why me?” ’
A lifelong keen runner and personal trainer, who now works as an exercise lead at the Parkinson’s Centre for Integrated Therapy at the University of Kent, Sarah has long wondered whether growing up in the countryside and running through fields and along rural footpaths might have triggered her disease by exposing her to agricultural pesticides.
She says: ‘That’s what I’ve put it down to. I’m also having genetic tests, as my father was adopted.’
She believes that regular running has helped stave off the disease and has allowed her to cut down her medication from three tablets a day to one.
Next month she will run the London Marathon to raise money for the charity Cure Parkinson’s, which is dedicated to finding a cure for the disease.
She adds: ‘Exercise is my medicine, and I want to keep it that way for as long as I can.’
While there has been no formal research on the subject in this country, Ms Bale points out that ‘there are more cases in farmers than you might expect’.
People who live near golf courses are also at risk because of the pesticides used to maintain the greens. One large US study last year found those living within one mile of a course had a 126 per cent higher risk of developing Parkinson’s compared with those living six miles away. However, the use of chemicals on golf courses is more tightly regulated here, and some courses, such as Minchinhampton Old Course in the Cotswolds, use no chemical pesticides or fertilisers.
Whatever the case, exposure to these chemicals is not the whole story, Prof Muqit points out.
‘Exposure isn’t enough – studies on pesticides in California suggest some people in families get Parkinson’s while others don’t,’ he says. ‘Why is that? We don’t know. But there’s likely to be an interaction with your genetics, your ability to deal with the chemicals – how your body absorbs them and metabolises them.’
Other chemicals associated with Parkinson’s are trichloroethylene (TCE) and perchloroethylene (PCE), which are commonly used in solvents, to degrease metals and in dry cleaning. Both are classified as cancer-causing by the International Agency for Research on Cancer (IARC), and regular exposure to TCE was linked with a six-fold increase in Parkinson’s risk, according to a twin study from 2011.
The chemicals can persist in soil and groundwater for years, and research from 2023 found higher rates of Parkinson’s among veterans who had been housed at Camp Lejeune, a US Marine Corps base in North Carolina which was contaminated by TCE and PCE during the 1970s.
Using TCE for dry cleaning stopped in the UK in the 1950s, while PCE use is tightly controlled and subject to local council permits. Reassuringly, no research yet suggests a ‘hotspot’ of Parkinson’s among those who work in the industry. Nor is anyone suggesting that consumers who use dry cleaning are at risk.
Emerging research has focused on whether common viruses can trigger the neurological changes seen in Parkinson’s, although it is ‘too early’ to say if Covid increases the risk
There is also emerging research on the effect of air pollution on the brain. Traffic fumes and smoke from woodburners contain toxic particulates called PM2.5, which are so small they can be inhaled deep into the lungs. This has long been linked with cardiovascular disease and dementia, but studies also found people living in densely populated areas or near main roads have a higher risk of Parkinson’s compared with those living in postcodes with cleaner air.
One analysis last year of more than 56 million US patient records by researchers from Johns Hopkins University School of Medicine found that every increase in PM2.5 concentration resulted in a 17 per cent higher risk of Parkinson’s disease dementia – a later stage of Parkinson’s that affects up to 80 per cent of people with the disease.
Similar emerging research has focused on whether common viruses can trigger the neurological changes seen in Parkinson’s.
Viruses can drive neurological diseases – Epstein–Barr virus, which causes glandular fever, can trigger multiple sclerosis, and varicella zoster virus, which causes chickenpox and shingles, is linked to dementia. But while some evidence links Parkinson’s with viruses, none is a ‘smoking gun’, says Prof Muqit.
After the 1918 global influenza pandemic, there was a surge in Parkinson-like symptoms. Studies have since indicated a slightly increased risk of Parkinson’s following infections such as flu and hepatitis C.
When it comes to Covid, however, it is ‘too early’ to say if it increases the risk, experts agree.
One 2021 study by Oxford academics found 0.11 per cent of a cohort of 236,000 patients diagnosed with Covid went on to develop ‘parkinsonism’ – symptoms including tremors, muscle stiffness and balance problems, but not necessarily Parkinson’s disease – within six months. This rose to 0.26 per cent among those treated in intensive care. While it is unclear how much Parkinson’s can be prevented, research suggests that some factors may be protective.
One – although it is, for obvious reasons, not recommended – is smoking. A far healthier option is drinking coffee – three to five cups a day may reduce Parkinson’s risk by around 30 per cent.
But the most convincing evidence is around the protective effects of exercise. ‘It increases the health of neurons and improves the clearance of protein clumps,’ says Prof Kunath.
The evidence suggests meeting NHS guidelines of 150 minutes of activity each week that raises the heart rate may reduce the risk by 20 to 30 per cent. While diet is not specifically linked to Parkinson’s, experts say eating a Mediterranean-style diet based on lean meats, fresh fruit, veg and nuts can only be beneficial. Prof Muqit adds: ‘If you have high blood pressure, high cholesterol or type 2 diabetes, that can increase your risk of dementia and how quickly you progress. It’s probably true for Parkinson’s – it just hasn’t been proven yet.’
Ultimately, it is up to you to try to lower your risk, regardless of your environment. ‘Many are exposed to these risk factors but only a small percentage of them will get Parkinson’s,’ says Prof Kunath. ‘No single one of these things definitively causes it. However, with the right lifestyle, you can reduce your risk.’
How Michael J Fox fought back
When Michael J. Fox was diagnosed with Parkinson’s disease in 1991, the Hollywood actor – then just 29 – was told that his life expectancy was somewhere between ten and 20 years.
More than three decades later, the Back To The Future star is alive and well – though markedly hampered by his condition. How did he do it?
Fox, now 64, says the first sign of the disease was a twitch in his little finger. Soon after, a neurologist diagnosed him with early-onset Parkinson’s.
Since then, Fox has taken a daily drug called levodopa. It replaces the brain chemical dopamine, which Parkinson’s patients do not produce in large enough quantities, leading to movement issues. While it cannot halt Parkinson’s, it can reduce some of the tremors and stiffness.
In 1998, Fox underwent a procedure called a thalamotomy to treat severe tremors. The surgery involves making a small cut in the area of the brain that controls movement. However, his tremors returned soon afterwards.
Fox, who set up the Michael J. Fox Foundation for Parkinson’s Research, has previously said he believes that scientists will find a cure for the disease in the next decade.
However, speaking in 2024, he said he does not believe he will be alive to see it.
Michael J. Fox takes a daily drug called levodopa, which replaces the brain chemical dopamine and can reduce some of the tremors and stiffness
