Smoking Cessation, Weight Change, and Risk of Dementia: A Prospective Cohort Study

Smoking cessation is universally prioritized for the prevention of cardiovascular disease and cancer, but its impact on dementia risk remains uncertain. We aimed to evaluate the associations of smoking cessation and postcessation weight gain with long-term risk of dementia and cognitive trajectories.

We conducted a prospective cohort study using data from the US Health and Retirement Study (1995-2020). A total of 32,802 dementia-free adults (mean age 60.5 years [SD 10.7]; 57.1% female) were included. Smoking status and body weight were assessed biennially through structured interviews. The primary outcome was incident dementia identified using the Langa-Weir algorithm, and the secondary outcome was cognitive function measured on a 27-point scale.

Over 25 years of follow-up (median 9.9 years, interquartile range 4.4-16.4 years), 5,868 dementia cases were documented. Compared with current smokers, individuals who quit during follow-up had a lower dementia risk after quitting (hazard ratio 0.84, 95% CI 0.73-0.95), similar to those who had quit before baseline (0.79, 0.72-0.87) and to never smokers (0.75, 0.69-0.83). The benefits of cessation were largely limited to participants with no or modest 2-year postcessation weight gain (≤5 kg). By contrast, the association of quitting accompanied by >10-kg weight gain was not statistically significant (1.33, 0.87-1.82). Restricted cubic spline analysis showed decreasing dementia risk with longer time since quitting, and the risk approached that of never smokers and plateaued at around 7 years after cessation. Cognitive trajectory analyses showed that quitting was associated with long-term slower cognitive decline (slope difference 0.19 points per decade, 95% CI 0.00-0.38) but no transient cognitive change (0.57; 95% CI -0.69 to 1.83), especially among those with minor weight gain (slope difference 0.23 per decade, 95% CI 0.03-0.43).

Smoking cessation was associated with a sustained lower dementia risk and slower cognitive decline, comparable to never smokers and those without short-term risk increase. However, postcessation weight gain may attenuate these advantages, highlighting the need for weight management in cessation programs. These findings should be interpreted cautiously, given the potential residual confounding and measurement error.