Smoking tobacco is linked to a reduction in brain volume, including both gray and white matter, according to new research published in Biological Psychiatry Global Open Science. The study highlights the potential long-term adverse effects of smoking on the brain, with heavier smoking related to more significant brain volume loss.
The motivation for this extensive study stems from the well-documented harmful effects of cigarette smoking on overall health, including diseases like cancer, heart, and respiratory conditions. Previous research has established a connection between smoking and brain-related issues, such as dementia and deterioration in brain matter. However, a critical question remained unanswered: does smoking cause brain volume reduction, or do people with reduced brain volume have a predisposition to smoke?
“The world’s population is aging and we have a wave of older people who will develop dementia. This aging of the population is a growing major public health problem and we need to focus on how we can improve the modifiable risk factors for dementia so that we can have a healthy older population,” said senior author Laura J. Bierut, the Alumni Endowed Professor of Psychiatry at Washington University in St. Louis.
The core of the study relied on data from the UK Biobank, a large-scale biomedical database and research resource. The researchers utilized the 2019 release of this data, which included detailed imaging data of participants. To ensure the integrity and relevance of their findings, the study team was selective about their sample. They included 32,094 participants, carefully excluding individuals with neurological conditions that could confound the results.
“The UK Biobank is an amazing database available to scientists around the world,” Bierut explained. “This unique resource allows us to finally examine the effects of smoking on the brain. This work adds evidence to the recommendation that quitting smoking is one way to reduce one’s risk of developing dementia.”
A critical component of the study was the use of high-resolution brain imaging. Participants’ brain volumes were assessed using T1-weighted scans, performed with a Siemens Magnetom Skyra 3T scanner. These scans are known for their ability to provide detailed images of the brain’s structure, allowing for precise measurement of total brain volume, gray matter volume, white matter volume, and cerebrospinal fluid volume.
Smoking behaviors were assessed through self-reported surveys taken at two different time points. The study classified participants into various categories based on their smoking history, including daily smokers and non-smokers. Additionally, the researchers quantified smoking intensity using a metric known as “pack years,” which considers the number of cigarette packs smoked per day and the number of years smoked.
The researchers found that individuals with a history of daily smoking had significantly lower total brain volume, gray matter volume, and white matter volume compared to non-smokers. Among these, the reduction in gray matter volume was particularly pronounced. Gray matter is crucial for processing information in the brain, and its reduction could have significant implications for cognitive functions.
Moreover, the study uncovered a dose-response relationship between smoking and brain volume reduction. This means that the more cigarettes a person smoked over time, as measured by pack years, the greater the reduction in their brain volume. This finding is particularly concerning as it suggests that not just smoking, but the intensity and duration of smoking, exacerbates the decline in brain volume.
The researchers also delved into specific regions of the brain affected by smoking. They found that smoking was associated with changes in certain areas of the brain, including regions involved in high-level functions like the superior frontal cortex, as well as in subcortical and cerebellar regions. These changes could have significant implications for understanding how smoking affects specific brain functions.
While the researchers found a strong correlation between the polygenic risk score for smoking and a history of daily smoking, this genetic predisposition had only a modest association with brain volume changes. This suggests that the changes in brain volume are more likely a consequence of smoking behavior itself rather than being driven by genetic factors.
“People who smoke have an ‘older’ brain,” Bierut told PsyPost. “Decreased brain size is correlated with aging (as well as cognitive decline and dementia) and so we can think of the results in this paper as demonstrating an accelerated aging of the brain. This paper is another piece of the puzzle linking cigarette smoking to cognitive decline and dementia.”
“Quitting smoking is one of the most important things that you can do for your health. This includes not only the health of your heart and lungs, but also the health of your brain. The more cigarettes you smoke and the longer you smoke, the more you age your brain. So – since we are living longer, it is important to keep your brain as young as possible for as long as possible.”
“The other thing I always say to people who are older and who smoke – it is never too late to quit,” Bierut added. “There are health benefits of quitting even later in life.”
Future research could examine the factors influencing susceptibility to the effects of smoking. “A major question is whether everyone is equally susceptible to the effects of smoking or whether some are more (or less) susceptible,” Bierut said.
“Given the age of this population, the participants smoked combustible cigarettes. However, people are now using other tobacco products – for example e-cigarettes. Important questions – Is the effect of smoking on the brain related to the thousands of toxic chemicals that are in combustible cigarette smoke? Does nicotine play any role in these brain changes?”
The study, “Investigating the Relationship Between Smoking Behavior and Global Brain Volume“, was authored by Yoonhoo Chang, Vera Thornton, Ariya Chaloemtoem, Andrey P. Anokhin, Janine Bijsterbosch, Ryan Bogdan, Dana B. Hancock, Eric Otto Johnson, and Laura J. Bierut.