"It really seems that nicotine protects against Parkinson's," Daniela Berg, head of the Clinic for Neurology in Kiel, told DW. "Nicotine does not only refer to smoking itself, passive smoking is just as much a part of it as tobacco chewing," Berg explained.
However, nicotine is not only found in tobacco, it's also found in nightshade plants such as potatoes, tomatoes and pepper. The amounts are very small, but nicotine — even in small amounts — has often been the main subject of studies.
"There is hardly anything other than nicotine that has been found to protect against Parkinson's," says Berg. Some studies conclude that smoking stimulates certain enzymes that inactivate nerve toxins.
"The effect of nicotine is not yet fully understood, but the fact is that people who smoke are less likely to develop Parkinson's disease. But of course you wouldn't advise anyone to smoke because there are far too many negative outcomes," said the neurologist.
How Parkinson's can be prevented and treated, and how and where the disease develops, are just a few aspects of the disease that are currently being researched internationally.
A question of genes
A study published in 2016 in the medical journal The Lancet shows the incidence of Parkinson's disease worldwide. Canada and North America lead the statistics, although both are highly developed regions with very good medical care. But this is not necessarily crucial.
"There are certain population groups that have a genetic predisposition and therefore have an increased risk of developing Parkinson's disease," explains Berg.
Some population groups in North America also have such a genetic predisposition. "We now know that mutations in certain genes could be the main cause of Parkinson's disease in this population group."
Genetic predisposition is not everything
The environment also plays a major role. Environmental toxins, which can be dangerous for the nervous system, include pesticides. Unlike in Germany and Europe, these were permitted in Canada and North America until recently. "These pesticides increase the risk of Parkinson's disease. They are very bad for cell metabolism," says Berg.
An example of the connection between environmental toxins and Parkinson's disease can also be found in South America. Scientists have found that people who break down the metal manganese there have an increased risk of developing Parkinson's disease. The trace element manganese is harmful for nerve cells.
How we live
It is the complex interaction between genes and the environment that promotes Parkinson's disease. "If there was a single factor, we could hope that we had already found it," said Berg. "Then we would be able to advise people accordingly and nobody would get Parkinson's."
Lifestyle also has a decisive influence on neurodegenerative diseases such as Parkinson's disease. This includes nutrition. Polyphenol-containing foods such as green tea, coffee and many other substances contained in red berries have a positive effect on nerve cells.
"They remove the bad metabolic products. They are particularly helpful in cases of oxidative stress, for example where poor metabolic products can damage the cells," explains Berg. In this sense, a Mediterranean diet is also recommended, as it is also helpful for the prevention of cardiovascular diseases.
Sport and exercise
Physical activity has a very important role to play. "People who exercise moderately to a lot in middle age have a substantially reduced risk of developing Parkinson's disease in old age," Berg told DW. These aspects were investigated in a large study.
"Compared to people who do little or no sport, the relative risk of developing Parkinson's was reduced by about 40 percent."
The overall "Japan" concept
The lifestyle in Japan is very different from that in western countries, like North America. In Japan, green tea is everywhere and Japanese people consume a lot of polyphenols during their lifetime, which reduce bad metabolic products in the body.
Nutrition, such as the frequent consumption of fish, and healing methods in Japan differ significantly from those in western countries.
"In Asia, for example, there is a root that contains dopamine. The people there do not take Parkinson's drugs, but the root. They have the same ingredients," explains Berg.
Berg also sees another possible explanation for the relatively low number of Parkinson's cases in Japan and Asia in general in genetic predisposition. "These people may have more protective genes than others. We know that there are simply people-specific genetic backgrounds."
It's a combination of numerous factors that protect the body. This also includes exercise.
Hardly any Parkinson's disease in Africa
In Africa the life expectancy of people is far lower on average than in the West. Parkinson's disease, however, mostly affects older people, and predisposition is also an important aspect in Africa.
"We are already different on the outside alone. Our fellow human beings in Asia look different from our fellow human beings in Africa and from us. This difference is also reflected in the way certain metabolic products are broken down in the cells," explains Berg. There are not only external differences, but also genetic ones, and these can be decisive.
Too few neurologists
The scientists agree on one thing: it's difficult to conduct a reliable study worldwide on which regions have the most Parkinson's cases and why.
After all, Parkinson's must first be diagnosed.
While there are good conditions for this in America and Europe, neurologists are lacking in Africa, and only very few of them are able to diagnose Parkinson's reliably.
In some African countries it's possible to count the number of neurologists on one hand, says Berg. "I know from colleagues in Africa that many people with neurological diseases have never seen a doctor before, let alone a neurologist."
Global phenomenon and global problem
According to The Lancet, Parkinson's cases have more than doubled worldwide in about 25 years, from 2.5 million patients in 1990 to 6.1 million in 2016, but it's difficult to determine why some regions have a much higher number of Parkinson's cases than others.
"There are plenty of hypotheses, but no precise reasons yet," says Berg.
If the data were clearer, much more could be done about Parkinson's disease. At the moment, however, this is still wishful thinking.