Curious if you have any links to support lower incidence of Parkinsons for smokers. I found this, which states that nicotine does not slow the disease once started: https://www.michaeljfox.org/news/nicotine-patch-not-benefici...
https://www.sciencedirect.com/science/article/abs/pii/S01674...
There have also been numerous studies that have found that starting nicotine once symptoms begin is too late, with little or no effect. It is hypothesized that there is some critical point that once crossed, nicotine no longer has an effect. Parkinsons is believed to slowly develop over years or decades, and nicotine stunts this early progression.