Men who quit smoking for a prolonged period drive down their overall risk for dementia compared with recent quitters and continuous smokers, results of a large longitudinal study just published online in the Annals of Clinical and Translational Neurology suggest. 

Compared with men who continuously smoked, those who quit for at least 4 years experienced a 14% decrease in dementia risk. This finding suggests a protective effect associated with long-term smoking cessation. Those who never smoked experienced a 19% lower risk for dementia over the same mean follow-up of 7 years.

“We would like to emphasize smoking as a risk factor for dementia,” Daein Choi, MD, from the College of Medicine at Seoul National University in Korea, told Medscape Medical News. “Our findings may help physicians encourage their patients to quit smoking.”

“We were quite surprised,” Choi added, to discover that those who quit smoking had a lower risk than continuous smokers. He and colleagues had expected little change because of the low regenerative capacity of central nervous system neurons.

Women were excluded from the main analysis because of the low smoking rates among Korean women.

The authors point out that previous studies examining the association between smoking and Alzheimer’s disease (AD) have been controversial.

Some early tobacco company–funded research suggested nicotine may improve cognitive function among primates. Clinical research also suggested smoking may confer a protective effect.

However, most of the evidence supporting a link between smoking and an increased dementia risk has focused on Western populations. The current study is the first, the authors note, to look at the effect of smoking cessation in a large Asian population.

For the study, investigators identified 51,849 men aged 60 years or older in the National Health Screening Cohort of the Korean National Health Insurance System.

Participants underwent physical examination and completed questionnaires about smoking and other factors during two assessment periods: 2002-2003 and 2004-2005. After exclusions, the final study cohort included 46,140 participants.

The investigators identified 12,672 continuous smokers, 4175 short-term quitters (cessation less than 4 years), 9268 long-term quitters, and 20,025 never-smokers on the basis of questionnaire responses.

Scores on the Mini-Mental State Examination, Clinical Dementia Rating, and/or Global Deterioration Scale identified cognitive dysfunction. In addition, International Classification of Diseases, 10th Revision, codes flagged the 1644 participants who developed dementia during study follow-up. 

The investigators conducted a multivariable analysis that adjusted for patient age, household income, physical activity, drinking habit, body mass index, change in body mass index, blood pressure, fasting serum glucose, total cholesterol, and Charlson Comorbidity Index.

As total tobacco exposure decreased from continual smokers to short-term quitters, long-term quitters, and never-smokers, the risk for developing overall dementia decreased. This trend was statistically significant (P = .001).

Compared with those who smoked continuously through both periods, long-term quitters had a decreased risk for overall dementia (hazard ratio [HR], 0.86), as did the never-smokers (HR, 0.81).

Choi and colleagues also assessed an association between smoking cessation and AD or vascular dementia. Never-smokers had an 18% decreased risk for AD compared with continual smokers (HR, 0.82). Long-term quitters experienced a 15% relative decrease and short-term quitters an 8% decreased risk.

In addition, long-term quitters had a 32% decreased risk for vascular dementia compared with continual smokers (HR, 0.68); those who never smoked had a 29% decreased risk (HR, 0.71) and short-term quitters experienced 19% lower risk (HR, 0.81).

SOURCE: https://www.medscape.com/viewarticle/901890#vp_2

REFERENCE: Choi et al: Effect of smoking cessation on the risk of dementia: a longitudinal study;  https://onlinelibrary.wiley.com/doi/full/10.1002/acn3.633