Quitting smoking, even in later life, could help slow down age-related memory problems, a study has found.
According to experts, the findings add to evidence that giving up cigarettes may help prevent dementia, but they stress that more research is needed.
A team from UCL (University College London) examined the impact of smoking on age-related cognitive decline, which is when a person's ability to think, learn and remember gets worse as they get older.
The study, published in the Lancet Healthy Longevity journal, included data from 9,436 people aged 40 and over from across 12 countries.
Half had quit smoking, while half had continued.
Researchers said "the association between smoking and cognitive health is well established," but the long-term benefits of quitting are "less clear."
Analysis of tests that measured memory and verbal fluency showed scores for people who had given up cigarettes declined more slowly in the six years after they quit.
For the smokers who quit, the rate of decline was about 20% slower for memory and 50% slower for verbal fluency.
Mikaela Bloomberg, of UCL's Institute of Epidemiology and Health Care, said: "Our study suggests that quitting smoking may help people to maintain better cognitive health over the long term, even when we are in our 50s or older when we quit.
"We already know that quitting smoking, even later in life, is often followed by improvements in physical health and well-being. It seems that, for our cognitive health, too, it is never too late to quit.
"This finding is especially important because middle-aged and older smokers are less likely to try to quit than younger groups, yet they disproportionately experience the harms of smoking.
"Evidence that quitting may support cognitive health could offer new compelling motivation for this group to try and quit smoking.
"Also, as policymakers wrestle with the challenges of an ageing population, these findings provide another reason to invest in tobacco control."
Co-author Prof Andrew Steptoe, also of UCL's Institute of Epidemiology and Health Care, added: "Slower cognitive decline is linked to lower dementia risk.
"These findings add to evidence suggesting that quitting smoking might be a preventative strategy for the disease. However, further research will be needed that specifically examines dementia to confirm this."
The latest Office for National Statistics (ONS) Annual Population Survey estimates about 11.9% of people aged 18 or over, or the equivalent of about six million, smoked cigarettes in the U.K. in 2023.
It is the lowest proportion of current smokers since ONS records began in 2011.
The figures suggest people aged 25 to 34 were most likely to smoke (14%) while those aged over 65 were least likely to smoke (8.2%).
Reacting to the findings of the UCL study, Julia Dudley, head of research at Alzheimer's Research U.K., said: "Smoking is linked to multiple serious health conditions, including cancer, heart disease and dementia, particularly Alzheimer's disease and vascular dementia.
"Quitting smoking can significantly reduce your risk of developing these diseases.
"As this is an observational study, it only suggests a link between cognitive decline and quitting smoking.
"Further research is needed to understand whether other factors contributed to the differences, such as demographic differences, socioeconomic background or alcohol consumption.
"Having other measures of cognition monitored, such as problem solving, would also give a bigger picture of the benefits of quitting smoking."
Professor Paresh Malhotra, group leader at the U.K. Dementia Research Institute Centre for Care Research and Technology and head of the division of neurology at Imperial College London, said: "It's increasingly clear that what's good for your heart and blood vessels is good for your brain and thinking.
"This study from UCL provides further evidence, showing that stopping smoking after the age of 40 is associated with better memory and language skills than if people continue to smoke.
"This adds further impetus to the need to help as many people as possible, at whatever age, quit smoking altogether."
