London: Middle-aged smokers who puff 40 cigarettes a day more than double their risk of developing Alzheimer`s disease, a study shows.
The study also found that heavy smoking greatly increased chances of another common form of dementia.
Scientists in the US followed the progress of more than 21,000 middle-aged men and women for an average of 23 years.
Those who consumed more than two packets of 20 cigarettes a day had a 157 percent higher chance of suffering from Alzheimer`s disease than non-smokers, reports the Daily Mail.
They also had a 172 percent increased risk of vascular dementia over the follow-up period, according to the journal Archives of Internal Medicine.
Vascular dementia is the most common form of the disease after Alzheimer`s, and is linked to poor blood supply to the brain.
Rachel Whitmer, from the Kaiser Permanente research institution in California, who led the research, 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."