Smoking Linked to Brain Shrinkage, Irreversible Even After Quitting

Summary: Researchers found that smoking causes the brain to shrink and age prematurely, a condition not reversible even after quitting smoking.

The study analyzed data from over 32,000 individuals in the UK Biobank, revealing a direct link between smoking, genetic predisposition, and reduced brain volume. This discovery emphasizes smoking as a modifiable risk factor for dementia, highlighting its damaging and irreversible impact on brain health.

The research provides vital insights into the long-term neurological consequences of smoking and the importance of smoking cessation.

Key Facts:

1. Smoking causes brain shrinkage, effectively aging the brain prematurely, and this damage is irreversible even after quitting.
2. The study analyzed data from the UK Biobank, involving over 32,000 participants, to establish the link between smoking, genetics, and brain volume.
3. The research reinforces the critical importance of quitting smoking to prevent further brain damage and reduce the risk of dementia.

Source: Washington University

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.”

Scientists have long known that smoking and smaller brain volume are linked, but they’ve never been sure which is the instigator. And there is a third factor to consider: genetics. Both brain size and smoking behavior are heritable. About half of a person’s risk of smoking can be attributed to his or her genes.

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.

Each pair of factors proved to be linked: history of smoking and brain volume; genetic risk for smoking and history of smoking; and genetic risk for smoking and brain volume. 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.

Using a statistical approach known as mediation analysis, the researchers determined the sequence of events: genetic predisposition leads to smoking, which leads to decreased brain volume.

“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.”

About this neuroscience research news

Author: Diane Duke Williams
Source: WUSTL
Contact: Diane Duke Williams – WUSTL
Image: The image is credited to Neuroscience News

Original Research: Open access.
“Investigating the relationship between smoking behavior and global brain volume” by Laura J. Bierut et al. Biological Psychiatry

Abstract

Investigating the relationship between smoking behavior and global brain volume

Background

Previous studies have shown that brain volume is negatively associated with cigarette smoking, but there is an ongoing debate about whether smoking causes lowered brain volume or a lower brain volume is a risk factor for smoking. We address this debate through multiple methods that evaluate directionality: Bradford Hill’s criteria, which are commonly used to understand a causal relationship in epidemiological studies, and mediation analysis.

Methods

In 32,094 participants of European descent from the UK Biobank dataset, we examined the relationship between a history of daily smoking and brain volumes, as well as an association of genetic risk score to ever smoking with brain volume.

Results

A history of daily smoking was strongly associated with decreased brain volume, and a history of heavier smoking was associated with a greater decrease in brain volume. The strongest association was between total gray matter volume and a history of daily smoking (effect size = −2964 mm³, p = 2.04 × 10⁻¹⁶), and there was a dose-response relationship with more pack years smoked associated with a greater decrease in brain volume. A polygenic risk score for smoking initiation was strongly associated with a history of daily smoking (effect size = 0.05, p = 4.20 × 10⁻⁸⁴), but only modestly associated with total gray matter volume (effect size = −424 mm³, p = .01). Mediation analysis indicated that a history of daily smoking mediated the relationship between the smoking initiation polygenic risk score and total gray matter volume.

Conclusions

A history of daily smoking is strongly associated with a decreased total brain volume.