Quitting cigarette smoking can help lower the risk for dementia but cutting down on smoking does not, new research suggests.
The researchers, led by senior author Dong Wook Shin, MD, DrPH, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea, found some unexpected results: Simply cutting back on cigarette use — but not quitting entirely — was associated with with a higher risk for dementia,.
This cohort study showed that smoking cessation was associated with a reduced risk of all dementia, including [Alzheimer’s Disease and vascular dementia], compared with sustained smoking intensity. However, smoking reduction was associated with an increased risk of dementia. Therefore, smoking cessation, not smoking reduction, should be emphasized in efforts to reduce the disease burden of dementia,” the researchers write.
The study was published online January 19 in JAMA Network Open.
Several observational studies have shown that smoking cessation is associated with a lower risk for dementia. However, the investigators note that their study is the first to examine the association between change in smoking intensity and dementia risk.
The cohort included 789,532 adults (96% male, mean age 52 years) in Korea who underwent biennial health examinations (2009 and 2011) and had current smoking status at the first health examination, with follow-up through the end of 2018.
Most of the participants had smoked for 20+ years (80%). By the 2011 examination, roughly 15% had quit smoking, 22% had reduced smoking, and 16% had increased cigarette use.
During a median follow-up of 6.3 years, there were 11,912 cases of dementia. This included 8,800 cases of Alzheimer’s disease (AD) and 1,889 cases of vascular dementia (VaD).
Smoking cessation was associated with decreased risk for dementia (8% decrease for all dementia, 6% for AD and 16% for VaD) compared with sustained cigarette smoking intensity.
This finding is consistent with previous studies that also showed smoking cessation was associated with decreased dementia risk, the researchers note.
The benefit of smoking cessation on risk for dementia was evident in younger but not in older age groups — suggesting that smoking cessation at a younger age is associated with greater benefit than smoking cessation at an older age.
“Sick Quitter” Phenomenon?
Surprisingly, compared with sustained smoking, reduced cigarette use was associated with increased risk of all dementia — 25% increased risk in those who decreased the number of cigarettes smoked per day by 50% or more and 6% increased risk in those who decreased the number of cigarettes smoked per day by 20%-50%.
“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,” the authors note.
Compensatory smoking among reducers is another potential explanation. “Reducers might inhale deeply to maintain their nicotine levels, negating any potential health benefit,” the investigators note.
“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 add.
Limitations of the study include the lack of information on education or apolipoprotein E ε4 level, which may be associated with risk for dementia, as well as the lack of information on second-hand smoking, type of tobacco used and duration of smoking cessation.
Also, the relatively short follow-up of 6 years may not be sufficient to fully elucidate the associations between changes in smoking and risk for dementia.
In addition, the effect size of smoking perception was relatively small (adjusted hazard ratio, 0.92). However, considering the prevalence of dementia and smoking rate, the public health implication would still be substantial, the authors note.
The study had no specific funding and the authors have declared relevant financial relationships.
JAMA Netw Open. Published online January 19, 2023. Full text
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