Role of smoking in inflammatory bowel disease: implications for therapy -- Thomas et al. 76 (895): 273 -- Postgraduate Medical Journal (Role of smoking in inflammatory bowel disease: implications for therapy)
Parkinson's Disease: Numerous studies have identified the uncanny inverse relationship between smoking and Parkinson's disease. Long-term smokers are somehow protected against Parkinson's, and it's not because smokers die of other things earlier. [10 Easy Paths to Self-Destruction]
The most recent, well-conducted study was published in a March 2010 issue of the journal Neurology. Far from determining a cause for the protective effect, these researchers found that the number of years spent smoking, more so than the number of cigarettes smoked daily, mattered more for a stronger protective effect.
Harvard researchers were among the first to provide convincing evidence that smokers were less likely to develop Parkinson's. In a study published in Neurology in March 2007, these researchers found the protective effect wanes after smokers quit. And they concluded, in their special scientific way, that they didn't have a clue as to why.
Mental Health & Brain: The most fascinating and widely recognized health benefit of smoking is its ability to seemingly alleviate symptoms of mental illnesses, including anxiety and schizophrenia. According to an article published in 1995 in Neuroscience & Biobehavioral Reviews, schizophrenics have much higher smoking rates than people with other mental illnesses, and appear to use it as a method of self-medicating. The article postulates that nicotine found in cigarettes reduces psychiatric, cognitive, sensory, and physical effects of schizophrenia, and also provides relief of common side effects from antipsychotic drugs.
The treatment of schizophrenia isn't the only positive effect that nicotine has on the brain. A series of very interesting studies from multiple academic sources confirms that the risk of Parkinson's disease and Alzheimer's disease is surprisingly higher in non-smokers than in smokers. Doctor Laura Fratiglioni of Huddinge University Hospital in Sweden states, "Cigarette smokers are 50% less likely to have PD or AD than are age- and gender-matched nonsmokers [...] cigarette smoking exerts an undefined, biologic, neuroprotective influence against the development of PD and AD."