Researchers found that dementia risk increases with the number of cigarettes smoked per day, rising by 16% for those who smoke 10 a day and by 34% for those who smoke 20, compared with people who have never smoked.
A scientific review involving about 2.8 million people found that smoking is associated with an increased risk of dementia, Alzheimer's disease and vascular dementia, with the risk rising as the number of cigarettes smoked per day increases.
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According to the study, which was led by researchers from Curtin University in Australia and published in the journal "eClinicalMedicine", smokers face a 31% higher risk of developing dementia compared with people who have never smoked.
The risk rose to 40% for Alzheimer's disease and to 52% for vascular dementia.
The researchers observed a link between the number of cigarettes smoked per day and the likelihood of developing dementia. People who smoke 10 cigarettes a day face a 16% higher risk, while the risk rises to 34% among those who smoke 20 cigarettes a day, compared with people who have never smoked.
Lead researcher Mario Serfo said the findings show the need to pay attention to the impact of smoking on brain health, alongside its well-known risks to the heart and lungs and the likelihood of developing cancer.
He added that the relationship between smoking and dementia becomes stronger as the number of cigarettes consumed increases.
Quitting smoking may reduce the risk of developing the disease
The study showed that people who had quit smoking do not face a higher risk of developing dementia compared with those who have never smoked, and that their risk is lower than that of people who continue to smoke.
However, the researchers explained that the study's findings do not prove a direct causal relationship between smoking and dementia, although they add to the scientific evidence suggesting that quitting smoking may help reduce the risk of developing the disease.
Blossom Stephan, a co-author of the study, called for brain health to be included in discussions about the risks of smoking and the health benefits of giving it up.
The researchers stressed the need to expand tobacco control campaigns so they also warn about the impact of smoking on brain function and cognitive abilities, in addition to its well-known risks to the heart and lungs and the likelihood of developing cancer.
In this context, they recommended including warnings about brain health on cigarette packs and incorporating them into smoking cessation programmes to raise awareness of the health consequences of tobacco consumption.
The researchers called for further studies to determine whether the timing of quitting smoking and the length of abstinence affect the level of dementia risk.
