Parkinson’s disease is the world’s fastest-growing neurological disease and pesticide exposure may be a factor. Is New Zealand still too liberal with sprays?
Martin Bennett had been spraying ragwort and thistles with his dad on the family’s Waikato dairy farm when, as they sat down for lunch, he noticed the pot plants in the dining room wilting. It was 1975, the year of Abba the band, Jaws the movie and, in New Zealand, the Māori land march and new PM Rob Muldoon. Bennett was 16.
He remembers when the manufacturers started dyeing the sprays pink so you could see where you’d been in the paddocks. He’d take a shower at the end of the day and notice the white sock line on his ankles beneath his bright pink legs. The only precaution he remembers taking in those days was “spraying with the wind”.
Now 65, Bennett is a decade on from his diagnosis of Parkinson’s disease and has become increasingly convinced that the pesticides he used so freely – and without protection – from a young age have contributed to the cause. It’s not a view he came to lightly. “I really am a facts-based person and I don’t follow wild theories.”
Science supports him. Farmers, and others exposed to pesticides in their jobs, are over-represented in Parkinson’s statistics. It’s a cruel disease, causing a range of symptoms, including shaking and tremors, rigidity, and balance and movement problems as a result of the loss of dopamine-producing cells in the brain.
Now, there are growing calls for greater restrictions on the chemicals. Leading that lobby is globally renowned Dutch consultant neurologist Professor Bas Bloem, a recent visitor to New Zealand, who says a Parkinson’s pandemic is upon us because of our exposure to toxins. He believes it is not ageing that causes Parkinson’s but environmental toxins.
Whereas rates of Alzheimer’s since 1990 have largely kept pace with the ageing population, the prevalence of Parkinson’s has doubled in the past 20 years and has been expected to double again in the next 20, making it the world’s fastest-growing neurological condition.
“The reality is even worse,” Bloem says. “The latest data in The Lancet shows growth is exceeding our worst expectations – we have already reached the number we expected to reach by 2035.”
Bloem’s target is pesticides (including herbicides and insecticides), the worldwide use of which has grown exponentially since World War II. Multiple studies have linked paraquat – banned in 67 countries but not New Zealand – to a higher risk of Parkinson’s.
Glyphosate, most used here as the popular weedkiller Roundup among others, has just been approved for use in Europe for a further 10 years, despite uncertainty over whether it increases the risk of Parkinson’s.
“The problem is we don’t know if current pesticides are safe because current regulatory actions are inadequate,” says Bloem, who’s ranked in the top 1% of the world’s most-cited scientists over the past decade and is co-editor-in-chief of the Journal of Parkinson’s Disease. He says more sophisticated laboratory safety testing is vital to reveal pesticides’ true impact on the brain. For example, 70% of dopamine-producing neurons have to be killed before Parkinson’s symptoms occur, but in lab tests on animals, no cell counts are taken in the brain to determine if those neurons are being lost.
“If a pesticide kills 60% of dopamine neurons, the animal looks perfectly sound and happy and the product goes onto the market despite it not being safe at all. We have to fight a powerful enemy, which is called industry.”
Test animals are also usually fed the products, whereas pesticides are normally inhaled or absorbed through the skin. Bloem wants to see the chemicals industry financially support moves to biological alternatives, and to compensate farmers affected by that change.
“There are alternatives and we may have to accept a worm or two in our potatoes.” He concedes he does not know what the impact on agriculture would be with a wholesale shift away from potentially dangerous chemicals. “I don’t know the exact answer. But I do know the risks for the brain.”
In late 2019, New Zealand’s Environmental Protection Authority banned four paraquat herbicides and placed stricter controls on the two remaining products by reducing rates of application and expanding buffer zones. Protective clothing and masks are mandatory.
Asked why paraquat wasn’t totally banned, the EPA’s manager of hazardous substances reassessments, Dr Shaun Presow, told the Listener it is important a number of different herbicides are available to farmers. “Otherwise, we end up in a situation where weeds develop resistance relatively quickly and have to move to harder and higher dosages.”
He does not think there is enough evidence to merit the sorts of tests Bloem is urging for glyphosate and says although there are epidemiological links with Parkinson’s, rules on use are stricter than they were in the past. He says inhalation tests are already done and regulators can seek brain-cell counts if they have concerns.
In July, after an application from the Environmental Law Initiative citing “significant new information” about the risks of glyphosate, the EPA decided there were no new grounds to review its approval.
“Staying optimistic is a challenge. All the time you are fighting and not really winning.”
Presow believes current restrictions around chemical use are addressing the risks. “We know that in the past, chemicals were not used in a way we would allow today. A lot of hazards weren’t known or understood, or when they were understood, farmers would occasionally not follow the rules. I believe what we are seeing here is a time lag between exposure to paraquat under a less-restrictive regime and development of the illness.”
About 13,000 New Zealanders have Parkinson’s, and the biggest research project into the condition is a 17-year longitudinal study led by Professor Tim Anderson of the New Zealand Brain Research Institute in Christchurch. More than 460 local people and 110 controls have enrolled in the study that involves regular neuropsychological testing, clinical staging, blood and DNA tests and brain scans, in an effort to find biomarkers of the disease that could be used for early diagnosis and monitoring progression.
Anderson’s team are also running an online study that is trying to recruit 500 people with Parkinson’s and 500 controls, questioning them about their lifestyle and exposure to toxins and collecting DNA samples. His group has also published a prizewinning paper, with its calculations indicating that depending on the age of onset of the condition, people with Parkinson’s need a different number of “hits” (toxin exposure, risk genes) before the condition develops. Parkinson’s in people under 45 required six “hits”, while those who developed it at an older age needed eight, reflecting increased genetic risk in younger-onset cases.
The number of New Zealanders with Parkinson’s has been steadily rising with our ageing population and is projected to reach 20,000 by 2040. Anderson says given the predictions, understanding the causes is critical for public prevention measures.
The search for a cure has been frustratingly slow. The best and most-prescribed medications are still drugs that are converted in the brain to dopamine or mimic the effects of dopamine – agents that have been on the market since the 1970s. But Bloem says a diabetes drug, Exenatide, has had promising results in early clinical trials in the UK, improving motor function and some cognitive issues. A phase 3 trial – a larger study required before a drug can be registered – is nearing an end.
“If the trial is positive, the world of Parkinson’s will change,” says Bloem.
He stresses that although he believes chemicals are a leading cause of Parkinson’s, there are others, including our genes and exposure to viruses and bacteria and repeated head trauma.
Mounting evidence
Auckland neurologist Dr Viswas Dayal agrees, but adds that scientific evidence is mounting against chemicals, saying several have the same effect in the brain as some of the genes identified as possible contributors.
“The PINK1 gene mutation damages the mitochondria of the cell. Paraquat also damages a specific protein in the mitochondria … it’s the same sort of mechanism.”
Although the disease is linked with industrial or occupational use of pesticides, Dayal has gone as far as stopping his use of fly sprays with automatic dispensers, and says he avoids inhaling fly spray fumes – although it’s hard to know when they’re around because many are odourless. The chemical in insect spray is permethrin, which has the same effect on mitochondrial function as paraquat.
He says he avoids making recommendations around personal use of pesticides, but is concerned on a population level – especially given that paraquat use in New Zealand has increased five-fold in the past 20 years.
The EPA says it has begun a safety review into synthetic pyrethroids, including permethrin, that are common spray ingredients. “They are considered extremely hazardous to the environment as well,” says Presow.
Viruses too
A New Zealand scientist who takes a “less toxiny view” of the triggers for Parkinson’s is Professor Maurice Curtis, co-director of the Neurological Foundation Human Brain Bank at the University of Auckland’s Centre for Brain Research. He believes viruses and bacteria are an important part of the mix, pointing to an outbreak of post-encephalitic parkinsonism likely triggered by the 1918 Spanish flu pandemic. He also notes recent studies showing areas of the brain, particularly those related to memory, reduced in size in Covid patients who’d had before-and-after scans.
Curtis’s team have studied the brains of Parkinson’s patients donated to the centre and found that abnormal clumps of the protein alpha synuclein, implicated in the development of Parkinson’s, occur first in the olfactory bulb. This accounts for the loss of the sense of smell – the “canary in the coalmine” of the disease – which can happen many years before typical symptoms develop.
The research could one day enable earlier diagnosis and treatment. Curtis’s team are now pulling together the patients’ medical records and interviewing family members to find out more about their lifetime exposures.
Exercise helps
Bas Bloem was the keynote speaker at Parkinson’s NZ’s 40th anniversary conference in Auckland in August, where he tempered his alarming message about the “Parkinson’s pandemic” with one of hope.
“I am an unofficial carrier of the mutation for the gene for optimism, so everything has to be seen in that perspective – I think you all deserve a better future and I think it is on the horizon.”
Drugs, gene therapies and surgical interventions such as deep brain stimulation aside, Bloem says one of the most powerful things Parkinson’s patients can do to maintain their health is regular aerobic exercise.
In trials, symptoms in patients who exercised regularly stabilised, while those who did not deteriorated. Brain scans showed shrinkage in non-exercisers, but among those who worked out, the brain not only stopped shrinking but also made new connections between the diseased basal ganglia (part of the network of brain cells and nerves that control voluntary movements) and healthy cortex (responsible for cognition).
“If I get diagnosed with Parkinson’s tomorrow, I will live on the treadmill. I will exercise my butt off.” Of course, Bloem, a former semi-professional volleyball player, already does, working out four times a week for 45 minutes at the gym. A pencil-slim 2.01m tall, he has no butt to work off.
Something as basic as regular bowel movements can also make a difference, he says. Slow bowel movements lead to changes in the gut microbiota, which interfere with the effects of medication.
While in New Zealand, he advocated for the establishment here of ParkinsonNet, regional networks of healthcare professionals who specialise in treating the condition, including not only neurologists and nurses, but also physiotherapists, occupational therapists, urologists, sex experts, gastroenterologists and pulmonary specialists. Bloem set up ParkinsonNet in the Netherlands in 2004 and says the improved care has reduced two of the leading causes of Parkinson’s death – aspiration pneumonia and hip fractures. It’s since been adopted in a number of other countries.
Specialists the Listener spoke to like the idea, but question whether New Zealand has the available workforce to establish the programme.
“This is something I’m sure should happen,” says Auckland City Hospital neurologist Dr Barry Snow, a Parkinson’s expert. He says nurse specialists would be a good option to staff it. “But we have big problems of access to good healthcare in New Zealand. We have distressingly long waiting lists, and we are making resource-based decisions a lot, which is not very good for patients. How do you turn that around in the face of the world’s fastest-growing neurological disorder?”
Bloem says it’s time for the Parkinson’s community to become activists in the cause of a safer environment. “I enjoy being part of this community – they are some of the nicest people on the planet.”
But, he told the conference, “you may be too friendly, too moderate. Maybe it’s time to slam your fist on the table and insist on more money for research, insist on better regulatory actions, insist on a rapid move to biological agriculture and make your voice heard, make yourself loud.”
No walk in the park
Back in Putāruru, dairy farmer Martin Bennett says although he still uses a herbicide, albeit with a mask, overalls and gloves, he “wouldn’t go within a mile” of paraquat. Though he concedes there’s not yet an alternative that does the job well enough, he’s using a product whose ingredients haven’t been linked with Parkinson’s.
He describes himself as one of the luckiest people around with the condition in that “I’m still running around doing things”. In August, he and his wife enjoyed a month-long holiday in Australia. A left-hander, he can no longer write with that hand and is now practising with his right. He has an excellent physiotherapist and has installed a swimming pool so he can swim regularly on the farm.
That said, he stresses Parkinson’s is “no walk in the park”. He needs to take medications six times a day, restrict his food intake and exercise relentlessly.
“Staying optimistic is a challenge. All the time you are fighting and not really winning.”
