Smoking is related to Brain Shrinkage

According to a study conducted by researchers at Washington University School of Medicine in St. Louis, smoking causes brain shrinkage. The good news is that quitting smoking prevents further brain tissue loss; but, quitting smoking does not restore the brain to its previous size. Because people’s brains naturally lose capacity as they age, smoking causes the brain to age prematurely, according to the study.

The findings, which were published in the journal Biological Psychiatry: Global Open Science, assist to explain why smokers are at such a high risk of age-related cognitive decline and Alzheimer’s disease.

“Until recently, scientists had 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 and Alumni Endowed Professor of Psychiatry Laura J. Bierut, MD. “But as we’ve started looking at the brain more closely, it’s become apparent that smoking is also really bad for your brain.”

Scientists have long suspected a link between smoking and reduced brain volume, but they have never determined which is the cause. There is also a third consideration: genetics. Both brain size and smoking habits are inherited. A person’s genes account for almost half of his or her risk of smoking.

Bierut and first author Yoonhoo Chang, a graduate student, analyzed data from the UK Biobank, a publicly available biomedical database containing genetic, health, and behavioral information on half a million people, mostly of European descent. Brain imaging was performed on a subset of over 40,000 UK Biobank participants to measure brain volume. The researchers examined de-identified data on brain capacity, smoking history, and genetic risk for smoking for 32,094 participants in total.

Each set of characteristics was found to be linked: smoking history and brain volume; genetic risk for smoking and smoking history; and genetic risk for smoking and brain volume. Furthermore, the relationship between smoking and brain volume was dosage dependent: the more packs a person smoked each day, the smaller his or her brain volume.

When all three factors were taken into account, the correlation between genetic risk for smoking and brain volume vanished, but the link between each of them and smoking habits remained. The researchers determined the chain of events using a statistical technique known as mediation analysis: genetic predisposition leads to smoking, which leads to decreased brain volume.

“It sounds bad, and it is bad,” remarked Bierut. “A decrease in brain volume is consistent with aging.” This is critical as our population ages, because both aging and smoking are risk factors for dementia.”

Regrettably, the shrinkage appears to be irreversible. The researchers discovered that persons who had quit smoking years previously had brains that were permanently smaller than those who had never smoked.

“You can’t undo the damage that has already been done, but you can avoid causing further damage,” he remarked. “Smoking is a risk factor that can be reduced.” To stop aging your brain and increasing your chances of dementia, there is only one thing you can do: stop smoking.”

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