Mid-life smokers run a higher risk of dementia

Heavy smoking in mid-life more than doubles the risk of developing Alzheimer's disease, a study has shown.

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.

Lead 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.