Could Rotorua's world-famous rotten egg sulphur pong be beneficial to Parkinson's disease sufferers?

It's a strange link to draw - but one that nonetheless has plenty of potential to explore, says an Otago University scientist who has just made the case in the New Zealand Medical Journal.

The relatively high concentrations of hydrogen sulphide (H2S) found in the Rotorua region - home to 80,000 people - has been a focus of toxicology research over recent years.

One study searching for any possible effects on asthma and chronic obstructive pulmonary disease found no increased risk for either condition, while another that surveyed more than 1600 residents also failed to find any links between exposure and cognitive effects.

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But the latter study did make one small association with higher H2S exposure and improved simple reaction time, including finger tapping scores.

Dr Yusuf Ozgur Cakmak, of Otago's Department of Anatomy, said this was a "tantalising" indication as finger-tapping was one motor-function that was used as an assessment method in Parkinson's disease.

There were also other clues in scientific literature to suggest the right concentration H2S could have a therapeutic benefit for Parkinson's symptoms.

"Hydrogen sulphide is in fact a gaseous neuro-transmitter, so it can help modulate neural function," Cakmak explained.

"But the lifetime of this transmitter is very short, so continuous inhalation is a must to have any benefit."

Recent research drawing on animal studies has just demonstrated that inhalation of H2S protected dopaminergic neurons, which were crucial for Parkinson's disease.

"In addition, other researchers have found out that this compound has got a modulatory function in the networks of Parkinson's disease-related structures.

"Interestingly, there's a new drug trial that includes hydrogen sulphide to Levodopa, which is a common drug used in Parkinson's disease."

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Cakmak said the key would be to determine just what concentrations of H2S could be beneficial.

Rotorua's ambient air chronic exposure levels were among the highest of anywhere in the world, with analysis previously suggesting residents were living amid mean concentrations of 20.8 parts per billion (ppb) of air at home and 27ppb at work.

These levels were well within safe bounds: studies have shown how H2S doesn't begin to irritate our eyes and lungs until levels reach 10,000 to 50,000ppb.

What wasn't known, however, was whether chronic exposure to such safe concentrations could be beneficial to motor functions of Parkinson's patients.

Yet there remained a potential biological basis, given the evidence from the animal studies, as well as indirect evidence of differences in Parkinson's patients' microbiota.

In humans, naturally low levels of H2S gas occur in the body and is synthesised by gut microbiota flora, as well by enzymes predominantly found in nervous system, liver and kidney tissue, and there have been recent suggestions this could also have implications for Parkinson's disease.

Cakmak now planned to set up an H2S experiment on Parkinson's disease patients by using the Rotorua's H2S levels as a proxy later this year.

He acknowledged any studies trying to find a statistically significant difference of Parkinson's rates and symptom severities in Rotorua residents, compared with other regions, would have to be detailed and normalised to account for ethnicity, smoking habits and age.

Parkinson's disease

• Parkinson's disease is the progressive degeneration of the dopamine-producing cells in the brain leading to symptoms that include tremors, stiffness and rigidity, and slowness of movement.

• It affects 1 to 2 per cent of Kiwis aged over 60 - about 10,000 people - and that rate is expected to double over the next 20 years.

• There is currently no cure, and symptoms typically only become clear after the sufferer has already lost 70 per cent of the dopamine-producing cells.

• The best-known treatments today include drugs and "deep brain" stimulation, where a stopwatch-sized device is implanted in the chest and a wire inserted into the brain to electrically stimulate the areas that control movement.