Smokers have a thinner outer brain layer than non-smokers, scientists have discovered.
Past studies have long linked smoking to heightened risk of cancer and lung disease.
And research has shown smokers are more likely to endure premature ageing, gum disease, go on to develop Alzheimer's and heart disease.
But if that long list is not reason enough to stub out your last cigarette, a new study has revealed the damaging effect smoking has on the brain.
Scientists in Edinburgh and Montreal found the brain cortex is thicker in non-smokers than smokers.
The cortex is the outer layer of the brain in which critical cognitive functions such as memory, language and perception take place.
They cautiously suggest that the cortex might regain some thickness once smokers quit the habit.
But they added that was not seen in all regions of the brain.
The study gathered health data and examined MRI scans of 224 men and 260 women with an average age of 73, around half of whom were former or current smokers.
The scientists from Edinburgh University and McGill University, 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.
Professor Ian Deary, from the University of Edinburgh, who led the research, said: 'It is important to know what is associated with brain health in older age.
'From these data we have found a small link between smoking and having thinner brain grey matter in some regions.
'There are findings in our study that could suggest that stopping smoking might allow the brain's cortex to recover some of its thickness, though we need further studies conducted with repeat measures to test that idea.'
His colleague Dr Sherif Karama, assistant professor of psychiatry at McGill University,added: '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.'
The apparent recovery process is slow though, and incomplete, he said.
Heavy ex-smokers in the study who had given up smoking for more than 25 years still had a thinner cortex.
Although the cortex grows thinner with normal ageing, the study found that smoking appears to accelerate the thinning process.
A thinner brain cortex is associated with adult cognitive decline.
Dr Karama, added: '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.
Those taking part in the study were participants 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 those people who had given up smoking for the longest period of time had a thicker cortex, compared to those who had recently quit.
That was the case, even after accounting for the total amount smoked in their lifetime.
Professor Joanna Wardlaw, director of the Brain Research Imaging Centre at the University of Edinburgh, said: 'The effects of smoking on the lungs and heart are well known, but our study shows that there are important effects on the brain as well, another good reason for not smoking.'
Professor James Goodwin, head of research at Age UK, added: 'Understanding how and why our thinking skills change with age is a major current health challenge.
'This work helps us to understand how smoking affects the brain in later life.
'The more we can find out about what influences our thinking skills as we age, the better the advice we can give people on protecting their cognitive health.'
The study is published in the journal Molecular Psychiatry and is part of a larger project called the Disconnected Mind that is supported by funding from Age UK.
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