The study at the Washington University School of Medicine in St. Louis, and published Tuesday in Biological Psychiatry: Global Open Science, set out to examine why smokers are at a higher risk for Alzheimer's and dementia.
"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," Bierut added.
The study examined the link between smoking and smaller brain volume along with a third factor, which is genetics. What researchers found was that genetics leads to a predisposition to smoking, which ultimately leads to decreased brain volume.
Researchers analyzed 32,094 people from UK Biobank, a public biomedical database with genetic, health and behavioral information on half-a-million people. Those involved in the smoking study underwent brain imaging. Researchers discovered that the more packs of cigarettes a person smoked a day, the smaller his or her brain volume was.
"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."
While quitting smoking will stop further brain shrinkage, the damage already done is irreversible, the study says. To prove their point, researchers analyzed people who had quit smoking years before and found that their brains remained permanently smaller than the brains of those who had never smoked.
"You can't undo the damage that has already been done, but you can avoid causing further damage," said Washington University graduate student Yoonhoo Chang.
"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."
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