Data from 21,123 people, surveyed between 1978 and 1985 when in their 50s and tracked for dementia from 1994 to 2008, has revealed that those who smoked more than two packs per day in middle age had more than twice the risk of developing dementia, both Alzheimer's and vascular dementia, compared to non-smokers.
A quarter of the participants (25.4%) were diagnosed with dementia during the 23 years follow-up, of whom a little over 20% were diagnosed with Alzheimer's disease and nearly 8% with vascular dementia.
Former smokers, or those who smoked less than half a pack per day, did not appear to be at increased risk. Associations between smoking and dementia did not vary by race or sex.
Smoking is a well-established risk factor for stroke, and is also known to contribute to oxidative stress and inflammation.