"I Thought Quitting Smoking Was Enough"...How Long It Takes to Reduce Alzheimer's Risk

Kyung Hee University Hospital Team Tracks 1.4 Million People for 10 Years

"Eight Years or More of Smoking Cessation Lowers Alzheimer's Risk by 42%"

A domestic study has found that the longer the smoking cessation period, the more the risk of Alzheimer's disease decreases in a stepwise manner.

A research team from the Department of Occupational and Environmental Medicine at Kyung Hee University Hospital tracked 1,403,636 adults for an average of 10.5 years, using data from the National Health Insurance Service from 2002 to 2023. Based on repeatedly confirmed smoking status during health checkups, participants were categorized as non-smokers, sustained quitters, or current smokers. Those who quit smoking temporarily and then resumed, or whose smoking status was inconsistent, were excluded from the "sustained quitters" group.

No Smoking Sign

As a result of the analysis, a total of 58,519 new cases of Alzheimer's disease were identified during the follow-up period. The risk of Alzheimer's disease among current smokers was 24.6% higher than that of non-smokers. Alzheimer's disease is the most common type of dementia, accounting for about 80% of all cases. The risk increases with age and it is also a major cause of geriatric dementia.

The risk of Alzheimer's disease decreased significantly as the duration of smoking cessation increased. By cessation duration, those who had quit for less than two years had a 10.1% lower risk of Alzheimer's disease compared to current smokers. The group that had quit for 2–3 years showed a 23.4% lower risk, the 4–5 years group a 17.6% reduction, and the 6–7 years group a 29.0% lower risk, respectively. For those who maintained smoking cessation for eight years or longer, the risk of Alzheimer's disease was reduced by as much as 41.8%.

The research team analyzed that these results are closely related to the biological damage caused by smoking to the brain.

Smoking increases oxidative stress in the body, triggers chronic inflammatory responses, and leads to deterioration of cerebrovascular function and damage to the blood-brain barrier. These changes promote the accumulation of amyloid beta and abnormal tau protein, which are key pathologies of Alzheimer's disease. In contrast, quitting smoking gradually alleviates such damage, leading to a gradual decrease in the risk of Alzheimer's disease.

The researchers noted that a reduction in Alzheimer's disease risk could be observed immediately after quitting smoking. Those who had quit for less than two years had a 13.6% higher risk of Alzheimer's disease compared to lifelong non-smokers, but their risk was still lower than that of current smokers. Furthermore, after more than two years of cessation, the risk level approached that of non-smokers. This suggests that while some cerebrovascular function and inflammatory responses begin to recover immediately after quitting, it takes time for the neurodegenerative damage accumulated by smoking to be sufficiently relieved.

The research team emphasized that, unlike previous studies, this study analyzed only Alzheimer's disease separately, not overall dementia. Most prior studies have analyzed "total dementia," which combines vascular dementia and Alzheimer's disease, but since smoking causes both vascular damage and neurodegeneration, distinguishing differences by disease type is necessary, according to the researchers.

The researchers stated, "Since Alzheimer's disease is a condition in which pathological changes progress gradually decades before onset, the effect of smoking cessation is also more pronounced when maintained over the long term rather than the short term," adding, "The most significant risk reduction was confirmed in the group that maintained smoking cessation for eight years or more, which supports this conclusion." The results of this study were published in the latest issue of the international journal Alzheimer's Research & Therapy.

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