Smoking Shrinks the Brain and Effectively Causes Premature Brain Aging

Smoking shrinks the brain, according to a study by researchers at Washington University School of Medicine in St. Louis. Since people’s brains naturally lose volume with age, smoking effectively causes the brain to age prematurely, the researchers said.

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, 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.

In total, the team analyzed de-identified data on brain volume, smoking history and genetic risk for smoking for 32,094 people.

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.

“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.”

Sources:

Yoonhoo Chang, Vera Thornton, Ariya Chaloemtoem, Andrey P. Anokhin, Janine Bijsterbosch, Ryan Bogdan, Dana B. Hancock, Eric Otto Johnson, Laura J. Bierut. Investigating the Relationship Between Smoking Behavior and Global Brain Volume. Biological Psychiatry Global Open Science, 2024; 4 (1): 74 DOI: 10.1016/j.bpsgos.2023.09.006

Materials provided by Washington University School of Medicine. Original written by Tamara Bhandari. Note: Content may be edited for style and length.

Washington University School of Medicine. “Smoking causes brain shrinkage, study finds.” ScienceDaily. ScienceDaily, 12 December 2023. <www.sciencedaily.com/releases/2023/12/231212163348.htm>.

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