This was a revelation for me: Edward Luttwak claims that nicotine played an important role in the scientific-industrial revolution because (a) it makes people smarter and (b) it kills them before they can go senile, preventing gerontocracy.
He's now 79 and doesn't want to die painfully of lung cancer, so he switched to patches some years ago.
It actually helps to prevent Alzheimers.
"A statistically significant inverse association between smoking and Alzheimer's disease was observed at all levels of analysis, with a trend towards decreasing risk with increasing consumption" (International Journal of Epidemiology, 1991)
"The risk of Alzheimer's disease decreased with increasing daily number of cigarettes smoked before onset of disease. . . . In six families in which the disease was apparently inherited . . . the mean age of onset was 4.17 years later in smoking patients than in non-smoking patients from the same family" (British Medical Journal, June 22, 1991)
"Although more data are needed . . . [an analysis of 19 studies suggests] nicotine protects against AD" (Neuroepidemiology, 1994)
Nicotine injections significantly improved certain types of mental functioning in Alzheimer's patients (Psychopharmacology, 1992).
One theory: nicotine improves the responsiveness of Alzheimer's patients to acetylcholine, an important brain chemical.
"When chronically taken, nicotine may result in: (1) positive reinforcement [it makes you feel good], (2) negative reinforcement [it may keep you from feeling bad], (3) reduction of body weight [by reducing appetite and increasing metabolic rate], (4) enhancement of performance, and protection against: (5) Parkinson's disease, (6) Tourette's disease [tics], (7) Alzheimer's disease, (8) ulcerative colitis and (9) sleep apnea. The reliability of these effects varies greatly but justifies the search for more therapeutic applications for this interesting compound." ("Beneficial Effects of Nicotine," Jarvik, British Journal of Addiction, 1991)
In this compilation of 19 studies, 15 found a reduce risk of Alzheimers in smokers, and none found an increased risk. Also noted is the fact that acute administration of nicotine improves attention and information processing in AD patients, which adds further plausibility to the hypothesis:
https://web.archive.org/web/20120715065033/http://www.forces.org:80/evidence/files/liars.htm#alz