Cutting Back on Smoking No Help for Dementia Risk

Quitting smoking was associated with a lower risk of dementia, but cutting back was linked with an even higher risk, according to a Korean cohort study.

In the study of nearly 800,000 participants, most of whom were men with a long history of smoking, those who quit over a median follow-up of 6.3 years had a significantly lower risk of all dementia compared with those who sustained their smoking habits (adjusted HR 0.92, 95% CI 0.87-0.97), reported Dong Wook Shin, MD, DrPH, MBA, of Sungkyunkwan University School of Medicine in Seoul, and co-authors.

However, smoking reduction — decreasing the number of cigarettes smoked by at least 50% per day — was associated with an increased risk of dementia versus those who sustained their smoking intensity (aHR 1.25, 95% CI 1.18-1.33), while a more modest increased risk was seen for those who started smoking more (aHR 1.12, 95% CI 1.06-1.18), they noted in JAMA Network Open.

“One possible explanation for this finding is the sick quitter phenomenon. A reduction or cessation of cigarette smoking could suggest behavioral changes toward a healthy lifestyle because of health concerns, considering the higher number of prevalent comorbidities in the reducer group than the sustainer group,” Shin and team wrote.

“In this context, the decreased risk of dementia associated with smoking cessation could be underestimated because of the sick quitter phenomenon. However, the protective association between smoking cessation and dementia despite the high number of comorbid conditions in those who quit suggests that the sick quitter or reducer phenomenon cannot solely explain the findings,” they continued.

Those who reduced their number of cigarettes by 20-50% per day saw a dementia risk that was not significantly different than the sustained smoking group (aHR 1.06, 95% CI 1.00-1.12).

Shin and colleagues emphasized the need for encouragement and support for patients intent on quitting smoking, rather than focusing on reducing their cigarette use.

“Despite the lack of benefits from smoking reduction for risk of dementia, a reduction-to-quit intervention may be an important first step toward smoking cessation,” they noted.

In analyses stratified by age, sex, and alcohol drinking, results were consistent with the main findings. The decreased risk of all dementia in participants who quit smoking was greater in those younger than 65 compared with those 65 and older (aHR 0.81 vs 0.97, P=0.003 for interaction), while there was no significant difference between men and women.

The decreased risk of all dementia for those who quit smoking was also more prominent among alcohol drinkers compared with nondrinkers (aHR 0.84 vs 1.02, P<0.001 for interaction).

This study included 789,532 participants ages 40 and older from the National Health Insurance Service database of Korea (95.8% men, mean age 52.2). They underwent biennial health exams in 2009 and 2011 and were current smokers at the first exam. They were followed until the end of 2018.

Nearly 35% had been smokers for 30 years or longer, and 80.2% had been smoking for 20 years or more.

At the time of the 2011 examination, 14.6% of participants had quit smoking, 21.9% had reduced smoking habits, and 15.9% had increased cigarette use. They were put into five groups, based on the changes made to their smoking intensity from the time of their first examination to their second: quitter, reducer I (at least 50% fewer cigarettes per day), reducer II (20-50% fewer per day), sustainer, or increaser (20% or more per day).

During the median 6.3-year follow-up, 11,912 dementia events, including 8,880 cases of Alzheimer’s disease and 1,889 cases of vascular dementia, were observed. Smoking cessation was associated with a significantly lower risk of vascular dementia (HR 0.84, 95% CI 0.73-0.97) but not Alzheimer’s disease (HR 0.94, 95% CI 0.88-1.01).

Shin and team acknowledged that the study being made up almost entirely of men was a limitation. In addition, they were unable to collect some information on dementia risk factors, such as education level and apolipoprotein E ε4 level. Information on second-hand smoking or use of products like electronic cigarettes was also not available.

In addition, they noted that “because dementia progresses insidiously during the early stages, a follow-up duration of 6 years may not be sufficient to fully elucidate the associations between changes in smoking and risk of dementia.”