Interesting point. I believe the studies of nicotine's effect on Parkinsons is being done with nicotine absent from tobacco. So, could it be that (given your example of China) there's something in tobacco cigarettes, perhaps another additive, that's negating the beneficlal effects of nicotine when it comes to Parkinsons? Just cogitatin'...
Could be .. or there is something in the bell peppers besides nicotine that's really the active ingredient ..