Smoking cessation, rather than reduction, linked to lower risk for dementia

Smoking cessation was associated with lower risk for dementia, including Alzheimer’s disease and vascular dementia, compared with sustained or even reduced smoking intensity, researchers reported in JAMA Network Open.

“Approximately 152 million individuals are expected to be affected by dementia by 2050,” Su-Min Jeong, MD, of the department of medicine at Seoul National University College of Medicine in South Korea, and colleagues wrote. “Smoking is a well-known risk factor for dementia and accounts for the third highest population-attributable percentage of dementia cases.”

Seeking to determine whether smoking cessation or reduction was associated with risk for dementia, Jeong and colleagues conducted a cohort study using data from the National Health Insurance Service database of Korea. They included participants aged 40 years and older who underwent health examinations in 2009 and 2011 and who were current smokers at the first visit.

Researchers surveyed participants according to duration of smoking and average number of cigarettes per day and categorized them quitters (stopped smoking), reducers I (decreased number of cigarettes smoked per day by at least 50%), reducers II (decreased number of cigarettes smoked per day by 20% to 50%), sustainers (maintained number of cigarettes per day by less than 20%) or increasers (increased number of cigarettes per day by at least 20%).

The primary outcome of interest was newly diagnosed dementia, identified by prescribed antidementia medication and diagnostic codes.

According to results, 789,532 participants (mean age, 52.2 years; 95.8% men) were included in the cohort. At the baseline examination, more than half of participants were heavy smokers (53.8%), while 37.5% were moderate smokers, and 8.8% were mild smokers. At the follow-up visit, 14.6% of participants had quit, and 21.9% had reduced smoking. More than 15% of participants increased cigarette smoking from 2009 to 2011.

During a median follow-up of 6.3 years, researchers reported 11,912 dementia events, including 8,800 Alzheimer’s disease and 1,889 vascular dementia events. Participants who had quit smoking had a significantly lower risk for all dementia (adjusted HR = 0.92; 95% CI, 0.87-0.97) compared with those who had maintained their smoking habits.

Conversely, participants who decreased the number of cigarettes smoked by at least 50% had a significantly higher risk for all dementia (aHR = 1.25; 95% CI, 1.18-1.33), as did those who increased the number of cigarettes smoked by 50% (aHR = 1.12; 95% CI, 1.06-1.18), compared with those in the sustainer group.

“This cohort study showed that smoking cessation was associated with a reduced risk of all dementia, including AD and [vascular dementia], compared with sustained smoking intensity,” Jeong and colleagues wrote. “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.”