We all know cigarette smoking is bad for our health (for example, higher rates of heart disease, respiratory disease, and cancer), but it also has an effect on our brains. Yup. Research shows it's associated with a decrease in brain size (volume)!
The researchers found that while all levels of daily smoking was associated with a decrease in brain volume, heavy smoking was associated with an even greater decrease in brain size (volume). This is a dose-response relationship.
By the way, this strong association between a history of daily smoking and overall brain volume, gray matter volume, and white matter volume of the brain was also found in other studies.
They also found that even if you stop smoking, you don't get back that missing brain volume. But at least it'll stop further cigarette smoking shrinkage. The researchers point out that this could explain why smoking is linked to increased rates of age-related cognitive decline and Alzheimer's. Yikes!
From Science Daily: Smoking causes brain shrinkage, study finds
Smoking shrinks the brain, according to a study by researchers at Washington University School of Medicine in St. Louis. 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.
"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."
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.
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.
"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.