Smoking is associated with a 50% lower incidence of Parkinson’s disease (PD) when compared to nonsmokers, but the mechanism is still unknown. Though there are many chemicals in tobacco that could theoretically be involved, several studies suggest that nicotine not only has a protective effect on the brain cells involved in PD but may also offer therapeutic benefit.
Approximately 1.5 million Americans suffer from Parkinson’s, with about 60,000 new cases diagnosed each year. PD is a progressive, neurodegenerative disease that occurs when certain types of nerve cells in the brain either die or become impaired. These nerve cells produce a neurotransmitter, or chemical messenger, called dopamine. The nerve cells involved in PD are responsible for allowing muscles to move smoothly, and when there is enough damage or cell loss, the characteristic symptoms of tremors, shuffling gait and impaired speech develop.
A recent study out of The Parkinson’s Institute in Sunnyvale, California, suggests that nicotine may protect nerve cells from the same type of damage that occurs in PD. In their study, monkeys were given a toxin that selectively kills dopamine-producing cells and creates the symptoms of PD. Some monkeys were given nicotine at a level similar to that found in human smokers, while the control group was not. The researchers found that the toxin created 25% less damage to the brain cells of the monkeys who were pre-treated with nicotine. Though this may not seem like a lot, it is important to understand that patients don’t typically have symptoms from PD until 80-90% of the cells are damaged. So the difference between having 80% damage and only 60% damage is the difference between having the disease and having no symptoms at all. Though certainly not a cure, the findings suggest nicotine may have a role in slowing the progression of the disease.
For those already suffering from PD, one of the mainstays of treatment has been levodopa, or L-dopa. Unfortunately, a common side-effect called dyskinesias (these are the jerky, uncontrollable movements often seen in PD patients) can be so severe that they can be worse than the original symptoms of PD. In a study recently published in the Annals of Neurology, researchers found a 50% reduction in L-dopa associated dyskinesias in monkeys who were pre-treated with nicotine. Though the mechanism is unknown, it appears that nicotine normalizes the release of dopamine or may adjust the levels of other neurotransmitters that control movement.
Scientists, of course, are quick to point out that they are not recommending that people smoke. The risks far outweigh the benefits. But when the risks of smoking are primarily caused by tobacco (and the myriad chemical additives), the benefits of nicotine alone certainly warrant more research.
