Smoking causes irreversible shrinkage of brain volume

Smoking has been identified as a factor contributing to the shrinkage of the brain, according to a study conducted by researchers at the Washington University School of Medicine in St. Louis. 

The study, published in Biological Psychiatry: Global Open Science, sheds light on the connection between smoking and a reduction in brain tissue, offering insights into why smokers face an elevated risk of age-related cognitive decline and Alzheimer’s disease.

Premature loss of brain volume

The research indicates that while quitting smoking prevents further loss of brain tissue, it doesn’t fully restore the brain to its original size. Consequently, smoking accelerates the aging process of the brain, causing it to lose volume prematurely, in addition to the natural age-related decline. 

Senior author Dr. Laura J. Bierut, an Alumni Endowed Professor of Psychiatry, emphasized that the impact of smoking on the brain has been overlooked until recently due to a focus on the well-known effects of smoking on the lungs and heart.

Focus of the study

“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. But as we’ve started looking at the brain more closely, it’s become apparent that smoking is also really bad for your brain,” explained Dr. Bierut.

The study aimed to disentangle the complex relationship between genes, smoking behavior, and brain size. Using data from the UK Biobank, a biomedical database with information on over 40,000 participants, the researchers explored the connections between genetic risk for smoking, smoking history, and brain volume. 

Dose dependent changes

Dr. Bierut and first author Yoonhoo Chang, a graduate student, analyzed de-identified data on brain volume, smoking history, and genetic risk for smoking for 32,094 people.

Moreover, the study found that the association between smoking and brain volume depended on the dose, with a higher number of packs smoked per day corresponding to smaller brain volume. 

Mediation analysis, a statistical approach, helped determine the sequence of events: genetic predisposition leads to smoking, which, in turn, leads to decreased brain volume.

Broader implications 

Thus, the study highlights the importance of recognizing smoking as detrimental not only to lung and heart health but also to brain health. 

As Dr. Bierut explained, the irreversible reduction in brain volume associated with smoking aligns with increased aging, which is significant as the population ages, considering that both aging and smoking are risk factors for dementia.

Irreversible effects

Moreover, the experts discovered that the shrinkage of the brain appears to be irreversible, as individuals who had quit smoking years before still exhibited permanently smaller brains compared to those who had never smoked. 

Despite the irreversibility of past damage, the study emphasizes the modifiable nature of smoking as a risk factor, encouraging individuals to quit smoking to prevent further harm to the brain and reduce the risk of dementia.

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