In 2010, the number of dementia diagnoses around the world was estimated at 36 million with numbers increasing and predicted to double every 20 years. In a study of 6000+ men (average age 56 years), those who smoked were linked to a more rapid cognitive decline. However, those who quit smoking at least 10 years before the start of the study had similar scores as non-smokers.
Archives of General Psychiatry, Feb 2012