Smoking cessation may reduce dementia risk for people who avoid major weight gain

Quitting smoking may be associated with a lowered risk of dementia, especially for people who avoid major weight gain after quitting, according to a study published May 20, 2026, in Neurology^®, the medical journal of the American Academy of Neurology. The study does not prove that quitting smoking lowers the risk of dementia and cognitive decline, it only shows an association.

People often worry about what happens after they quit smoking - including weight gain and associated metabolic changes. What we found is that quitting is still associated with better brain outcomes but maintaining your weight may help preserve those benefits."

Hui Chen, PhD, of Zhejiang University School of Medicine in Hangzhou, China

The study looked at 32,802 middle-aged and older people without dementia at the start of the study. They had an average age of 61 and were followed for an average of 10 years. A total of 20% were current smokers, 36% were past smokers and 43% had never smoked.

Participants were interviewed every two years about smoking status, body weight and health.

Researchers figured out who developed dementia by using memory and thinking tests to check how well people could think, and by asking people who knew them about their memory and behavior.

Over the study period, 5,868 people developed dementia. Current smokers developed dementia at a rate of 1.5 cases per 100,000 person-years, compared to 1.6 cases per 100,000 person-years for those who quit during the study. Person-years represent both the number of people in the study and the amount of time each person spent in the study. People who quit smoking were on average four years older than those who did not quit.

After adjusting for factors such as age, physical activity and cardiovascular health, people who quit smoking had a 16% lower risk of dementia compared with people who continued smoking.

They found that compared with people who continued to smoke, those who quit had a sustained lower risk of dementia, with risk levels similar to people who had never smoked. The benefit increased with time since quitting, with dementia risk approaching that of never smokers after about seven years.

However, researchers found that weight changes after quitting smoking influenced these benefits. People who gained no to moderate weight, or up to 11 pounds (5 kilograms), after quitting continued to show a lower dementia risk and slower cognitive decline. In contrast, those who gained substantial weight, or 22 pounds (10 kilograms) or more, did not receive a cognitive benefit.

"Our findings suggest that quitting smoking may support long‑term brain health, but they also highlight that what happens after quitting matters," Chen said. "Future research is needed to better understand how weight management and other lifestyle factors can help people maximize the cognitive benefits of quitting smoking as they age."

A limitation of the study was that participants reported their smoking habits and weight rather than being monitored and may not have remembered everything accurately.