Quitting Smoking Significantly Lowers Alzheimer's Risk: When Do the Benefits Begin?

A new study has found that the risk of Alzheimer's disease decreases incrementally the longer a person remains smoke-free.

A research team from the Department of Occupational and Environmental Medicine at Kyung Hee University Medical Center announced these findings after tracking 1,403,636 adults for an average of 10.5 years, based on data from the National Health Insurance Service spanning from 2002 to 2023.

Alzheimer's disease is the most common form of dementia, accounting for approximately 80% of all cases.

The risk of developing the disease increases with age, making it a leading cause of senile dementia.

The research team categorized participants into non-smokers, sustained quitters, and current smokers based on their smoking status repeatedly confirmed during health checkups.

Individuals who had temporarily quit but resumed smoking, or those with irregular smoking patterns, were excluded from the sustained quitter group.

The analysis revealed that 58,519 new cases of Alzheimer's disease occurred during the follow-up period, and the risk for current smokers was 24.6% higher than that for non-smokers.

Quitting smoking showed a clear pattern of reducing the risk of Alzheimer's disease as the duration of abstinence increased.

By duration of smoking cessation, those who had quit for less than 2 years had a 10.1% lower risk of Alzheimer's compared to current smokers.

Subsequently, the risk decreased by 23.4% for the 2–3 year cessation group, 17.6% for the 4–5 year group, and 29.0% for the 6–7 year group.

For those who maintained long-term smoking cessation for 8 years or more, the risk of Alzheimer's disease dropped by 41.8%.

The research team analyzed that these results go beyond a simple statistical correlation and are deeply related to the biological damage smoking inflicts on the brain.

Existing research indicates that smoking increases oxidative stress in the body, triggers chronic inflammatory responses, and causes deterioration of cerebrovascular function and damage to the blood-brain barrier.

These changes are known to promote the accumulation of amyloid-beta and abnormalities in tau protein, which are the core pathologies of Alzheimer's disease.

Conversely, the research team interprets that quitting smoking may gradually alleviate this damage, thereby slowly reducing the risk of Alzheimer's disease.

In particular, the team noted that signs of a reduced risk of Alzheimer's appeared immediately after quitting.

In fact, while those who had quit for less than 2 years still had a 13.6% higher risk of Alzheimer's compared to lifetime non-smokers, their risk was lower than that of current smokers.

For those who quit for 2 years or longer, the risk level showed an effect approaching that of non-smokers.

This is interpreted to mean that while some cerebrovascular function and inflammatory responses begin to recover immediately after quitting, a certain amount of time is required for the neurodegenerative damage accumulated from smoking to be sufficiently mitigated.

The research team emphasized the significance of this study, noting that unlike previous research, it analyzed Alzheimer's disease separately rather than grouping it under overall dementia.

Most previous studies have analyzed total dementia, which combines vascular dementia and Alzheimer's disease. The research team explained that since smoking causes both vascular damage and neurodegeneration, it is necessary to distinguish between the differences in each disease.

The research team stated, "Because Alzheimer's disease is a condition where pathological changes progress slowly for decades before onset, the effects of quitting smoking are more pronounced when maintained over the long term rather than the short term," adding, "The fact that the most significant risk reduction was confirmed in the long-term cessation group of 8 years or more proves this."

The results of this study were published in the latest issue of the international journal, Alzheimer's Research & Therapy.

(Photo: Yonhap News)
※ Please note: This article was translated by AI and may contain errors.