Quitting smoking may reduce a person’s risk of developing dementia by 16 percent, according to a new study that also suggests the cognitive benefits can be undone by significant weight gain after giving up cigarettes. The findings, drawn from a decade-long analysis of more than 32,800 American adults, add fresh urgency to smoking cessation efforts in the UK, where nearly a million people live with dementia and the condition has become the nation’s biggest killer.
Researchers at Zhejiang University School of Medicine in China analysed data from the University of Michigan’s U.S. Health and Retirement Study, following participants who were interviewed every two years about their smoking habits, body weight and overall health. Over the course of the study nearly 6,000 people developed dementia, assessed through memory and thinking tests as well as reports from people close to them. The rate of dementia among those who continued to smoke was higher than among those who quit, and people who gave up smoking saw their dementia risk fall to levels similar to people who had never smoked.
Weight gain and dementia risk
Yet the protective effect was not uniform. Those who quit and did not gain weight saw the strongest reduction in risk, while participants who gained 22 or more pounds after stopping smoking experienced no significant reduction at all. By contrast, people who gained up to 11 pounds still saw a measurable benefit. The findings highlight a complex interaction between smoking cessation and post‑quit weight changes, which may offset some of the neurological advantages.
“Our findings suggest that quitting smoking may support long‑term brain health, but they also highlight that what happens after quitting matters,” said Hui Chen, a researcher at Zhejiang University School of Medicine, in a statement.
Smoking is one of the biggest lifestyle risk factors for dementia, estimated to double a person’s chance of developing the condition. It harms the brain by narrowing blood vessels and causing oxidative stress, while also increasing the risk of cardiovascular disease and stroke. However, obesity in midlife is itself a recognised modifiable risk factor for dementia. In the UK, where an estimated 982,000 people currently have dementia — a figure projected to reach 1.4 million by 2040 — the findings underscore the importance of supporting quitters not only to stop smoking but also to manage their weight afterward.
The NHS offers free stop‑smoking services across England, Scotland and Wales, including nicotine replacement therapy, prescription medications and digital support through the Quit Smoking app. People who use these services are three times more likely to quit successfully. The study suggests that such support could be complemented by advice on healthy eating and physical activity to help maintain a stable weight after quitting.
Study limitations and broader context
The researchers stress that the study does not prove that quitting smoking directly reduces dementia risk — it only shows an association. Participants self‑reported their smoking habits and weight, which introduces potential inaccuracies. “Future research is needed to better understand how weight management and other lifestyle factors can help people maximise the cognitive benefits of quitting smoking as they age,” Chen added.
The findings add to earlier work, including a December study that reported similar results in middle‑aged adults, and past research linking smoking cessation to a reduced risk of lung disease — itself a known risk factor for dementia. Dementia remains incurable, robbing people of their memories, personality and ability to communicate. It is a leading cause of death in the United States, responsible for more than 450,000 deaths each year, and cases are projected to nearly double to 13 million by 2050 as the population ages. In the UK, dementia killed more than 76,000 people in 2024, making it the country’s leading cause of death, with women disproportionately affected. The condition already costs the UK economy £42 billion annually, a figure expected to rise to £90 billion by 2040.
Despite the U.S. cigarette smoking rate hitting an all‑time low, more than 49 million American adults still use tobacco products, and the U.S. Centers for Disease Control and Prevention says tobacco use remains the leading cause of preventable death and disease.
