Researchers have identified an association between cigarette smoking and the loss of gray or white matter in a person’s brain.
The researchers who carried out the study are from the Uniformed Services University (USU), Bethesda, Emory University, Atlanta, and the University of Vermont, Burlington.
Their results suggest that there may also be an association between smoking and diseases such as Alzheimer’s and some dementias that are characterized by a loss of brain matter volume.
The research appears in the journal Neuropsychopharmacology.
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As the authors of the latest investigation note, past research has also linked smoking to various cognitive and mental health issues, including major depressive disorder, alcohol use disorder, and “lower processing speed, poorer general cognitive ability, poorer decision-making, and increased impulsivity.”
However, one challenge for scientists trying to investigate smoking’s impact has been understanding to what extent it is the cause of some of these issues rather than other confounding factors that often relate to smoking.
The latest study is significant not only because it is one of the largest of its type — including more than 17,000 participants — but also because the authors took into account various confounding factors.
As the researchers note, “The association between smoking and brain structure is particularly difficult to establish, as smoking has several common psychiatric, cardiovascular, and demographic risk factors that are also linked to brain morphometry.”
By accounting for these risk factors, the authors were able to demonstrate a link between smoking and the loss of brain matter volume more definitively.
The authors drew on data from the UK Biobank, which is one of the largest neuroimaging databases in the world.
Looking at MRI scans of people’s brains, the team looked for links between people who smoked — including whether they smoked most days, how many cigarettes they smoked, and how long for — and the relative volume of both their white and gray brain matter.
The researchers also accounted for various other factors related to brain health, including “age, sex, ethnicity, income, education, BMI, alcohol use, cardiovascular risk factors, years since quitting smoking, and global gray and white matter.”
Looking at all their data, the team established an association between smoking and reduced white and gray brain matter volume.
In particular, they found a clear association between smoking and white matter hyperintensities — a type of lesion in the brain that scientists associate with Alzheimer’s disease, dementia, other forms of cognitive impairment, and stroke.
As Joshua Gray, assistant professor of medical and clinical psychology and neuroscience at USU, notes, “Cigarette smoking is known to elevate risk for neuropsychiatric conditions such as depression and dementia.”
“We found that smoking is associated with multiple aspects of brain structure, in particular with increased white matter lesions. White matter lesions are linked to many of the same neuropsychiatric diseases as smoking.”
– Joshua Gray
A limitation of the study is that while it can demonstrate an association between smoking and brain health, it is unable to demonstrate a causal relationship.
Hence, rather than smoking causing the loss of brain matter volume, the relationship between the two could be more complex.
However, the authors believe there are good reasons to think the causal relationship runs from smoking to loss of brain matter volume.
Gray concludes, “Although further research is needed to understand to what extent smoking is a cause or consequence of these aspects of brain structure, our findings suggest a mechanism that links smoking to increased risk for dementia, depression, and other brain diseases.”