Mid-life smokers run a higher risk of dementia
Smoking more than 40 cigarettes a day also greatly increased rates of another common form of dementia.
Researchers in the US followed the progress of more than 21,000 middle-aged men and women for an average of 23 years.
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Hide AdLead researcher Dr Rachel Whitmer, from the Kaiser Permanente research institution in Oakland, California, said: "This study shows that the brain is not immune to the long-term consequences of heavy smoking.
"We know smoking compromises the vascular system by affecting blood pressure and elevates blood-clotting factors, and we know vascular health plays a role in risk of Alzheimer's disease."
Study participants were enrolled into a dementia survey between 1978 and 1985, when they were 50 to 60; 1,136 were eventually diagnosed with Alzheimer's and 416 with vascular dementia.
Ex-smokers or those who had fewer than ten a day, did not appear to face an increased risk.