Quitting smoking may cut the risk of developing dementia by 16 percent, according to research published in the journal Neurology that followed more than 32,800 American adults over a decade.
The study, drawing on data from the University of Michigan’s U.S. Health and Retirement Study, found that participants who gave up cigarettes during the ten-year period were significantly less likely to develop the chronic condition than those who continued smoking. Nearly 6,000 people in the study developed dementia, assessed through tests of memory and thinking abilities and reports from people around them. The rate of dementia among quitters fell to a level similar to that of people who had never smoked.
“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 China, in a statement.
The weight gain factor
The protective effect of quitting was not automatic, however. Researchers observed a crucial nuance: people who gained 22 pounds or more after stopping smoking saw no reduction in dementia risk. By contrast, those who put on up to 11 pounds still experienced a clear benefit, and the risk reduction was most pronounced for individuals who avoided any weight gain at all.
The finding underscores the complex interplay between smoking cessation and metabolic health. Weight gain is a common side effect of quitting, as nicotine suppresses appetite and boosts metabolism. The researchers suggest that substantial post‑cessation weight gain may counteract some of the cognitive advantages gained by eliminating tobacco’s harmful effects, possibly through increased inflammation, insulin resistance, or other mechanisms linked to obesity and brain health. The study did not prove causation — participants self-reported their smoking habits and weight — but the pattern was consistent across the large sample.
“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.
UK research reinforces the message
The findings echo a separate body of work from British researchers. A study published in The Lancet Healthy Longevity by University College London (UCL) scientists, using data from more than 9,000 participants across 12 countries including the UK, found that quitting smoking in middle age or later was linked to slower age‑related cognitive decline. In the six years after stopping, former smokers experienced roughly 20 percent slower decline in memory and 50 percent slower decline in verbal fluency compared with continuing smokers — equivalent to three to four months less memory loss and six months less fluency loss per year of ageing. UCL researchers concluded it was “never too late to quit” for cognitive health.
The UCL study strengthens the case that quitting smoking may be an effective preventative strategy against dementia, a condition for which there is no cure. Dementia already robs people of their memories, personality and ability to communicate, and it is the UK’s biggest killer. In 2024 it accounted for more than 76,000 deaths, or 11.9 percent of all deaths nationally. Across the UK, an estimated 982,000 people are currently living with dementia, a figure projected to rise to 1.4 million by 2040. The economic impact is estimated at £42 billion annually through costs to the NHS, social care and unpaid care.
In England alone, 483,000 people aged 65 and over had a formal dementia diagnosis as of March 2025 — a record high — yet around 40 percent of those thought to be living with the condition remain undiagnosed. For younger onset dementia (symptoms beginning before age 65), diagnosis rates are even lower; approximately 70,800 people in the UK are affected. NHS stop smoking services offer free support, including nicotine replacement therapy and medications through programmes such as “Quit Your Way,” reflecting the government’s long‑term ambition to create a smoke‑free generation.
Limitations and context
The Neurology study does not prove that quitting smoking directly causes a lower dementia risk — it only shows an association, the researchers stress. Because participants reported their own smoking status and weight, recall bias and other unmeasured factors could influence the results. The findings add to earlier work suggesting similar benefits in middle‑aged adults and to past studies linking smoking cessation to reduced lung disease, itself a risk factor for dementia.
In the United States, where the study was conducted, the cigarette smoking rate has fallen to an all‑time low, yet more than 49 million American adults still use tobacco products. Dementia cases in the US are projected to nearly double to 13 million by 2050, driven by environmental and lifestyle factors as well as an ageing population. The US Centers for Disease Control and Prevention states that tobacco use remains the leading cause of preventable death and disease.