Another reason to stop smoking: it increases dementia risk from brain shrinkage – but quitting, at any age, helps
This is the 37th instalment in a series on dementia, including the research into its causes and treatment, advice for carers, and stories of hope.
If you’ve ever smoked – or lived with a smoker – you may be familiar with the breathlessness and early morning cough that come with the habit.
The impact on the lungs is obvious – a smoker directly inhales a poison, after all. But smoking’s damaging effect on the brain may be less apparent.
A recent study throws this into the spotlight: habitual smoking causes the brain to shrink, it suggests.
Dr Laura Bierut, a psychiatry professor at Washington University School of Medicine in the US state of Missouri, led the study, published a few months before World No Tobacco Day on May 31.
She admits scientists once paid less attention to the effects of smoking on the brain, “in part because we were focused on all the terrible effects of smoking on the lungs and the heart”.
As we have grown more concerned about brain health, and started looking at the brain more closely, it has become apparent that smoking is also really bad for your brain, she says.
“People who smoke are more likely to have deterioration in grey and white matter,” Bierut adds, noting that this may help explain why some researchers estimate 14 per cent of global Alzheimer’s disease cases are linked to cigarette smoking.
A Swedish study on smoking and the brain examined the brains and smoking habits of women over more than 30 years. It found that cigarette smoking was associated with shrinkage in the frontal lobe.
The frontal lobe is responsible for managing many elements of thinking and behaviour, including emotions, personality, judgment, and self-control. It also supports memory storage. And memory loss is an early marker of dementia.
The vascular risks that come with smoking – including stroke, which is a significant risk factor for dementia – are exacerbated by the toxins in cigarette smoke, which cause inflammation and stress in cells, which have both been linked to Alzheimer’s disease.
Dr Joshua Gray, associate professor in the departments of medical and clinical psychology, and of neuroscience at the Uniformed Services University in Washington, led a large 2020 study on the effects of smoking on the brain.
Quitting at an early age (40 years) can reduce excess mortality by 90 per cent. In other words, risks are reduced to levels only slightly higher than never-smokers
The results, he says, suggest that smoking is one of the top risk factors for dementia, associated with a 1.6 times greater likelihood of developing the disease.
“It exerts numerous damaging effects through oxidative stress,” he says. Inflammation, and atherosclerotic processes such as hardening of the arteries, can translate into brain atrophy, which was shown in both the studies referenced above and in dozens of others.
Atherosclerosis is the thickening or hardening of arteries caused by a build-up in vessel linings.
“We found in our study that smoking was linked to reduced grey matter and increased white-matter hyperintensities” – meaning lesions, Gray says. The lesions are closely linked to a higher risk of dementia and stroke. (White matter describes the nerve fibres that connect different areas of the brain to each other and to the spinal cord.)
The brain consumes 20 per cent of the oxygen the body uses to function. It is especially vulnerable to oxidative stress – an imbalance between harmful free radicals and the body’s natural defence mechanisms – that damages structures inside brain cells and can cause cell death.
Oxidative stress also disrupts the balance of essential proteins, like amyloid-beta peptides. Studies suggest this contributes to the build-up of amyloid plaque in the brain that is a marker for Alzheimer’s disease.
Inflammation is cited as a cause for many diseases, including dementia; experts speak of brain “inflammaging” – ageing accelerated through inflammation.
Atherosclerosis impairs blood flow, which can have serious consequences for brain health for obvious reasons – it deprives the brain of oxygen and important nutrients, so is a risk for vascular dementia.
The chemicals inhaled through smoking (and from second-hand smoke) damage blood vessels, which raises the risk of developing atherosclerosis.
According to the US Food and Drug Administration, there are more than 7,000 chemicals in cigarettes and cigarette smoke. Nicotine and tar are the most talked about. Others include acetone, found in nail polish remover; arsenic, used in rat poison; and lead, found in batteries.
A pregnant woman who smokes may be harming not only her brain but her unborn child’s, too. A 2023 study published by researchers at University of California, Irvine, found that gestational nicotine disrupts receptors that sustain and regulate central nervous system activity.
Tobacco smoke exposure during pregnancy has been linked with a smaller head circumference at birth, reflecting the smaller size of a newborn baby’s brain – which may affect brain development in the long term.
Quitting smoking brings broad benefits to smokers and those close to them, Gray stresses – the earlier, the better for the brain, and other organ systems.
“Quitting at an early age (40 years) can reduce excess mortality by 90 per cent,” he says. “In other words, risks are reduced to levels only slightly higher than never-smokers.
“Even stopping smoking after 60 years old has been shown to substantially reduce the risk for dementia.”
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