Studies have shown that smoking does lower the risk of developing Parkinson's disease, as Reuters explains. Moreover it's not how much is smoked, but how many years smoked, that appears to be the protective factor.
Parkinson's disease is a neurologically degenerative disease characterized by several problems, including tremors, slowed movement, rigid muscles, impaired posture and balance, slurred speech, and even loss of automatic movement, such as blinking or swinging the hands when walking. Scientists are not sure why smoking appears to lower the risk factor. However, knowing that it does may help researchers to understand and treat the disease.