"Our study is the first to investigate dietary nicotine and risk of developing Parkinson's disease," said Dr. Searles Nielsen. "Similar to the many studies that indicate tobacco use might reduce risk of Parkinson's, our findings also suggest a protective effect from nicotine, or perhaps a similar but less toxic chemical in peppers and tobacco."
Tobacco and solanaceae plants have in common a lot of chemicals, including multiple alkaloids like atropine. Potato plants fall into the same family, as do all chili pepper plants. While this is an interesting study, it does NOT confirm that nicotine is the chemical in solanaceae that is protective against Parkinson's disease, even before you take into account that this was only a retrospective study.