Smoking may increase dementia risk by disrupting vital communication channels between the lungs and the brain.
Previous research has shown that heavy smoking in midlife is linked to more than double the risk of developing dementia, including Alzheimer's disease, decades later.
Now, a study from the University of Chicago suggests nicotine could trigger a previously unknown biological pathway that helps explain this connection.
The researchers discovered that specialised lung cells called pulmonary neuroendocrine cells (PNECs) release tiny particles, known as exosomes, in response to nicotine.
These exosomes interfere with how the brain regulates iron, a process essential for healthy nerve cells.
Disrupted iron balance can damage neurons, trigger stress on their energy systems and contribute to processes linked to neurodegenerative diseases such as Alzheimer's and Parkinson's.
'This research establishes a clear "lung-brain" axis that may help explain why cigarette smoking is linked to cognitive decline,' said co-author and postdoctoral researcher Kui Zhang.
The study, published in Science Advances, relied on laboratory models and stem-cell-derived PNECs.
While the results are promising, the researchers caution that more studies are needed to confirm the mechanism in humans.
'The lung is not just a passive target of smoke exposure, but an active signalling organ influencing brain health,' said co-author Asst. Prof. Joyce Chen of the UChicago Pritzker School of Molecular Engineering and the Ben May Department for Cancer Research.
The team is now exploring whether blocking the exosomes could eventually lead to therapies that protect the brain from smoke-induced damage.
Britain's smoking rate has fallen to a record low, but progress is slowing, and some areas are seeing worrying reversals.
The latest figures from the Office for National Statistics show that 9.1 per cent of adults smoked in 2024, around 4.9 million people.
At the same time, an estimated 5.4 million adults now use e-cigarettes, meaning vaping has overtaken smoking for the first time in the UK, particularly among younger adults.
Despite the overall decline, some areas have seen increases in smoking compared with a decade ago.
Public health experts warn that falling cigarette sales do not always translate directly into equivalent drops in smoking rates, as people may switch to vaping or seek non-legal tobacco products.
Ministers are seeking to accelerate progress through the proposed Tobacco and Vapes Bill, which would create a 'smoke-free generation.'
Anyone born on or after 1 January 2009 would never be legally allowed to buy tobacco.
The bill also includes measures to tighten controls on vaping, including restrictions on advertising, flavours, and packaging.
More than 1,200 health professionals - including doctors, nurses, and public health leaders - have backed the proposals, saying they are essential to reduce smoking and prevent a new generation from becoming addicted to nicotine.