Study Shows Quitting Smoking Doesn’t Fully Restore Brain Size

A recent study conducted by researchers at Washington University School of Medicine in St. Louis suggests that smoking is likely associated with a reduction in brain size, a phenomenon linked to age-related cognitive decline and an increased risk of Alzheimer’s disease. Although quitting smoking can prevent further loss of brain tissue, the study reveals that the brain does not fully recover to its original size post-smoking cessation. The research emphasizes that smoking effectively accelerates the aging process of the brain. 

Published in Biological Psychiatry: Global Open Science, the study sheds light on the often-overlooked impact of smoking on the brain. Senior author Dr. Laura J. Bierut, the Alumni Endowed Professor of Psychiatry, highlights that while the focus was historically on the adverse effects of smoking on the lungs and heart, closer examination reveals that smoking is also detrimental to the brain. 

The connection between smoking and smaller brain volume has been known for some time, but determining whether smoking causes a reduction in brain size or if smaller brains predispose individuals to smoking has been challenging. Genetics adds another layer to the complexity, as both brain size and smoking behaviour are heritable, with approximately half of an individual’s smoking risk attributed to their genes. 

To unravel the intricate relationship between genes, brains, and behaviour, the researchers, led by first author Yoonhoo Chang, a graduate student, analysed data from the UK Biobank—a comprehensive biomedical database containing genetic, health, and behavioural information on over 500,000 people, predominantly of European descent. 

The subset of more than 40,000 UK Biobank participants underwent brain imaging to determine brain volume. The analysis of de-identified data on brain volume, smoking history, and genetic risk for smoking for 32,094 individuals revealed interconnected links between smoking history and brain volume, genetic risk for smoking and smoking history, and genetic risk for smoking and brain volume. 

Moreover, the study found that the association between smoking and brain volume was dose dependent. Individuals who smoked more packs per day exhibited smaller brain volumes. When considering all three factors together, the link between genetic risk for smoking and brain volume disappeared, highlighting the sequential relationship: genetic predisposition leads to smoking, which, in turn, leads to a reduction in brain volume. 

Dr. Bierut expresses concern about the implications of brain volume reduction, stating, “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.” 

Despite the grim findings, the study suggests that the shrinkage in brain size is irreversible. Analysing data from individuals who had quit smoking years before, the researchers found that their brains remained permanently smaller compared to those who had never smoked. 

Yoonhoo Chang emphasizes the importance of smoking cessation as a preventive measure: “You can’t undo the damage that has already been done, but you can avoid causing further damage. Smoking is a modifiable risk factor. There’s one thing you can change to stop aging your brain and putting yourself at an increased risk of dementia, and that’s to quit smoking.” The study underscores the urgency of addressing smoking as a modifiable risk factor for preserving brain health and reducing the risk of cognitive decline in aging populations. 

Journal Reference  

Yoonhoo Chang et al., Investigating the Relationship Between Smoking Behavior and Global Brain Volume, Biological Psychiatry Global Open Science (2023). DOI: 10.1016/j.bpsgos.2023.09.006