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NEW YORK (Reuters Health) - People who use a particular class of blood pressure drug may have a decreased risk of developing Parkinson's disease, a new study suggests.The medications in question are a type of calcium channel blocker called dihydropyridines -- which include drugs like nifedipine (brands such as Adalat), felodipine (Plendil) and nicardipine (Cardene). Researchers found that among the more than 11,000 Danish adults in their study, those who were using the medications were more than one-quarter less likely to develop Parkinson's disease than people not on the drugs. No similar protective effect was seen with other types of calcium channel blockers, or with other classes of blood pressure drugs, including beta-blockers, angiotensin-II antagonists and ACE inhibitors. The findings, published in the Annals of Neurology, do not prove that dihydropyridine calcium channel blockers directly lower Parkinson's disease risk."This is the first study showing this in humans," said lead researcher Dr. Beate Ritz, of the University of California Los Angeles, and further studies are needed to see whether the association holds up. However, Ritz told Reuters Health, the findings are in line with the mechanisms by which calcium channel blockers operate, and with animal research showing that one of the drugs -- isradipine -- may protect dopamine-producing brain cells from becoming over stressed and damaged. Parkinson's disease is marked by the destruction of dopamine neurons (nerve cells), which help regulate movement.Unlike most neurons in the brain, dopamine neurons are "pacemakers" that generate their own rhythmic activity with the help of particular calcium channels, which allow calcium ions to pass into cells. The theory is that dihydropyridine calcium channel blockers, by inhibiting those channels, may protect dopamine neurons from becoming over stressed. The drugs -- with the exception of one, called amlodipine (Norvasc) -- are able to cross from the blood circulation into the brain. In line with that fact, Ritz and her colleagues found that while other dihydropyridines were associated with a lower Parkinson's risk, amlodipine was not. The study, which was funded by the U.S. National Institutes of Health, is based on information from Denmark's national system of databases, which allowed the researchers to link individuals' hospital records and drug-prescription information. They looked at the prescription histories of 1,931 adults who were diagnosed with Parkinson's between 2001 and 2006, and those of 9,651 healthy adults the same age and sex.Overall, dihydropyridine use was linked to a 26 percent to 30 percent reduction in Parkinson's risk. The findings, according to Ritz, raise the possibility that calcium channel blockers could someday be used to treat Parkinson's -- by helping to preserve patients' remaining dopamine neurons -- or to prevent the disease.In the latter case, that would depend on whether researchers can discover any "biomarkers" that identify people at increased risk of Parkinson's -- akin to cholesterol tests for gauging heart disease risk. But all of these questions, Ritz said, require much more research.