Smokers tend to have a thinner outer brain layer than non-smokers, new research suggests.
Scientists found that in people who have avoided smoking, the brain cortex - the layer which is important for thinking skills - is thicker than among smokers.
They cautiously suggest that the cortex might regain some thickness once smokers quit, but that this was not seen in all regions of the brain.
The study gathered health data and analysed MRI scans of 244 males and 260 females with an average age of 73, around half of whom were former or current smokers.
They analysed how a person's smoking habit was linked with the thickness of the brain's cortex using detailed MRI brain scans, careful image analysis and statistical models.
The research was carried out by scientists at the University of Edinburgh and the Montreal Neurological Institute at McGill University in Montreal, Canada.
The study found a small link between smoking and having thinner brain grey matter in some regions, and also that stopping smoking might allow the brain's cortex to recover some of its thickness.
The group tested were part of the Lothian Birth Cohort 1936, a group of individuals who were born in 1936 and took part in the Scottish Mental Survey of 1947.
Researchers found that participants who had given up smoking for the longest time had a thicker cortex compared with those who had given up recently - even after accounting for the total amount smoked in their lifetime.
Edinburgh's Professor Joanna Wardlaw said the effects of smoking on the lungs and heart were well known, but the new study showed that there were important effects on the brain as well.
The study is published in the journal Molecular Psychiatry and is part of a larger project called the Disconnected Mind.