Scientists from the Montreal Neurological Institute at McGill University and the University of Edinburgh report new evidence that long-term smoking could cause thinning of the brain's cortex. This outer layer of the brain is where critical cognitive functions such as memory, language, and perception take place. The researchers also note that stopping smoking helps to restore at least part of the cortex's thickness.

The study (“Cigarette smoking and thinning of the brain’s cortex”), which appears in Molecular Psychiatry, involved 244 male and 260 female subjects. Their average age was 73. The test group included current smokers, ex-smokers, and non-smokers. All of the subjects were examined as children in 1947 as part of the Scottish Mental Survey. Researchers used health data gathered during recent personal interviews with the subjects, and also analyzed data from MRI scans showing the current state of the subjects' brain cortices.

“We found that current and ex-smokers had, at age 73, many areas of thinner brain cortex than those that never smoked. Subjects who stopped smoking seem to partially recover their cortical thickness for each year without smoking,” says the study's lead author Sherif Karama, M.D., assistant professor of psychiatry at McGill University, psychiatrist at the Douglas Mental Health University Institute and an affiliate of the Montreal Neurological Institute.

“However, it took [approximately] 25 years for complete cortical recovery in affected areas for those at the mean pack-years value in this sample,” wrote the investigators. “As the cortex thins with normal aging, our data suggest that smoking is associated with diffuse accelerated cortical thinning, a biomarker of cognitive decline in adults. Although partial recovery appears possible, it can be a long process.”

“Smokers should be informed that cigarettes could hasten the thinning of the brain's cortex, which could lead to cognitive deterioration. Cortical thinning seems to persist for many years after someone stops smoking,” says Dr. Karama.

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