Smokers are more than twice as likely to develop Alzheimer's Disease as people who have never smoked, according to new research.
The study - the largest ever of its kind and the first major research to look at people before they develop Alzheimer's - followed 5,369 men and women aged 57 and over.
None of the people had Alzheimer's, the most common form of dementia, before the study by the Erasmus Medical School in Rotterdam began.Over a two-year period, any who developed signs of dementia were assessed and, where possible, given a brain scan.
A total of 107 people developed dementia during the course of the study, with 97 being diagnosed as having Alzheimer's. People who smoked were found to be 2.3 times more likely to develop Alzheimer's than those who had never smoked.
They were also more likely to get Alzheimer's at a younger age.
However, the researchers found that smoking does not increase the risk of developing Alzheimer's for people with a gene linked to the disease. Indeed, they believe smoking may offer protection against the disease for people with the gene - APOE epsilon 4.
The Dutch researchers said this could be because smoking altered the chemistry of the brain and defused some of the effects of Alzheimer's. Another reason could be the fact that many smokers do not live long enough to develop the disease, which particularly affects the very elderly.