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

Objectives

To assess the associations of smoking cessation and post-cessation weight gain with the risk of dementia and cognitive trajectories.

Design

Prospective cohort study.

Setting

The U.S. Health and Retirement Study (1995-2020).

Participants

A total of 32,802 dementia-free participants were included, with a mean age of 60.5 years (SD 10.7) and 57.1% female.

Exposure

Smoking status and body weight were collected biennially via structural interviews.

Main outcome measures

Dementia was identified using the Langa-Weir algorithm. Cognitive function was assessed using a 27-unit scale. Cox proportional hazard models estimated hazard ratio (HR) of dementia by smoking cessation status, subsequent weight change, and duration of cessation. Among participants who quit during follow-up, linear mixed models assessed cognitive trajectories before and after cessation.

Results

Over 25 years of follow-up, 5,868 dementia cases were documented. Compared with current smokers, individuals who quit during follow-up had a lower dementia risk after quitting (HR: 0.82, 95% confidence interval: 0.72-0.93), similar to those who had quit before baseline (0.76, 0.69-0.83) and to never smokers (0.72, 0.66-0.79). The benefits of cessation were largely limited to participants with no or modest weight gain (≤5 kg). By contrast, quitting accompanied by >10 kg weight gain was marginally associated with higher dementia risk (1.31, 0.95-1.80). Dementia risk declined steadily with increasing cessation duration, reaching the level of never smokers after approximately 5-7 years. Cognitive trajectory analyses showed that quitting was associated with long-term slower cognitive decline but no transient change, especially among those with no or modest weight gain.

Conclusions

Smoking cessation was associated with a sustained lower dementia risk and slower cognitive decline, comparable to benefits observed in never smokers and without evidence of a short-term risk increase. However, substantial post-cessation weight gain may attenuate these advantages. Smoking cessation programs should incorporate weight-management strategies to optimize long-term brain health.

SUMMARY BOX

• What is already known on this topic

• Smoking cessation is universally prioritized for reducing cardiovascular and cancer risk.

• Weight gain commonly occurs after quitting and can lead to adverse metabolic outcomes.

• So far, few studies have examined how cessation timing, duration, and post-cessation weight changes influence long-term dementia risk.

What this study adds

• In this study of 32,802 U.S. middle-aged and older adults, smoking cessation was associated with a steadily declining dementia risk, reaching the level of never smokers after approximately 5-7 years.

• Substantial post-cessation weight gain may attenuate these advantages, and the lower risk following cessation were largely limited to participants with no or modest weight gain (≤5 kg).

• Smoking cessation was also associated with long-term slower cognitive decline with no transient change, especially among those with no or modest weight gain.