“It Sounds Bad, and It Is Bad”
By WASHINGTON UNIVERSITY SCHOOL OF
MEDICINE
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The good news is that quitting smoking prevents further loss of brain tissue — but still, stopping smoking doesn’t restore the brain to its original size. Since people’s brains naturally lose volume with age, smoking effectively causes the brain to age prematurely, the researchers said.
The findings, published in Biological Psychiatry: Global Open Science, help
explain why smokers are at high risk of age-related cognitive decline and Alzheimer’s disease.
The Neglected Effects of Smoking on the Brain
“Up until recently, scientists have
overlooked 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,” said senior
author Laura J. Bierut, MD, the Alumni Endowed Professor of Psychiatry.
“But as we’ve started looking at the brain more closely, it’s become apparent
that smoking is also really bad for your brain.”
Link Between Smoking, Brain Size, and Genetics
Scientists have long known that smoking and
smaller brain volume are linked, but they’ve never been sure which is the
instigator. And there is a third factor to consider: genetics. Both brain size
and smoking behavior are heritable. About half of a person’s risk of smoking
can be attributed to his or her genes.
To disentangle the relationship between genes, brains, and behavior, Bierut and first author Yoonhoo Chang, a graduate student, analyzed data drawn from the UK Biobank, a publicly available biomedical database that contains genetic, health and behavioral information on half a million people, mostly of European descent.
A subset of over 40,000 UK
Biobank participants underwent brain imaging, which can be used to determine
brain volume. In total, the team analyzed de-identified data on brain volume,
smoking history, and genetic risk for smoking for 32,094 people.
Interplay Between Genetics, Smoking, and Brain Volume
Each pair of factors proved to be linked:
history of smoking and brain volume; genetic risk for smoking and history of
smoking; and genetic risk for smoking and brain volume. Further, the
association between smoking and brain volume depended on dose: The more packs a
person smoked per day, the smaller his or her brain volume.
When all three factors were considered
together, the association between genetic risk for smoking and brain volume
disappeared, while the link between each of those and smoking behaviors
remained. Using a statistical approach known as mediation analysis, the
researchers determined the sequence of events: genetic predisposition leads to
smoking, which leads to decreased brain volume.
Irreversible Consequences and Prevention
“It sounds bad, and it is bad,” Bierut said.
“A reduction in brain volume is consistent with increased aging. This is
important as our population gets older, because aging and smoking are both risk
factors for dementia.”
And unfortunately, the shrinkage seems to be
irreversible. By analyzing data on people who had quit smoking years before,
the researchers found that their brains remained permanently smaller than those
of people who had never smoked.
“You can’t undo the damage that has already
been done, but you can avoid causing further damage,” Chang said. “Smoking is a
modifiable risk factor. There’s one thing you can change to stop aging your
brain and putting yourself at increased risk of dementia, and that’s to quit
smoking.”
Reference: “Investigating the Relationship
Between Smoking Behavior and Global Brain Volume” by Yoonhoo Chang, Vera
Thornton, Ariya Chaloemtoem, Andrey P. Anokhin, Janine Bijsterbosch, Ryan
Bogdan, Dana B. Hancock, Eric Otto Johnson and Laura J. Bierut, 6 October
2023, Biological Psychiatry Global Open Science.
DOI: 10.1016/j.bpsgos.2023.09.006
