Smoking Shrinks the Brain, and Quitting Doesn’t Restore Size: Study

The findings help explain why smokers have a higher risk of developing age-related cognitive decline and Alzheimer’s disease.

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Smoking cigarettes shrinks the size of the brain, and stopping doesn’t reverse the damage, a new study shows. The findings help explain why smokers have a higher risk of developing age-related cognitive decline and Alzheimer’s disease.

But there’s good news: As soon as someone stops smoking, the shrinking stops.

The study, published in Biological Psychiatry: Global Open Science, looked at data from 32,094 individuals of European descent who smoked daily. The data came from the UK Biobank, a biomedical database available to the public that contains genetic, health, and behavioral information on about 500,000 people.

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The research team from Washington University School of Medicine in St. Louis found that total brain volume, including gray and white matter, decreased when a person smoked daily. Gray brain matter decreased more than white brain matter did, according to the analysis. Gray matter houses neural cell bodies, axon terminals, and dendrites; much of it is found in the cerebellum, cerebrum, and brain stem. It’s responsible for the central nervous system, which enables a person to control movement, memory, and emotions. White matter is filled with bundles of axons coated with myelin. Its job is to send signals up and down the spinal cord when the brain receives a stimulus.

The analysis of the UK Biobank data shows that the more a person smoked, the more brain mass they lost. That smoking affects the brain isn’t entirely new information, the research team admitted.

“The adverse effect of smoking extends into the brain, and this is shown by the association between smoking and dementia,” they wrote.

The research team noted that areas such as the hippocampal area, which is affected by Alzheimer’s disease, are particularly affected by daily smoking.

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“This finding is consistent with smoking, which has been identified as a risk factor for Alzheimer’s disease, accelerating the development of this illness,” the research team wrote.

In fact, the researchers suggested that 14 percent of Alzheimer’s cases across the world could be attributed to smoking.

Alcohol Also Reduces Brain Volume

In addition to smoking, the team found that drinking alcohol also has adverse effects on the brain. Like smoking, heavy alcohol use can reduce brain size, specifically subcortical brain volume. The subcortex is involved in overseeing emotions, memory, and hormone production. Subcortical structures also help people maintain their posture, gait, and other movements.

The risk of developing Alzheimer’s disease or dementia occurs even after someone stops smoking or drinking alcohol, researchers noted, because the brain damage is permanent.

Scientists believe that Alzheimer’s disease is caused when proteins build up in and around brain cells, sort of like plaque on teeth. One of these proteins is called amyloid, and another is called tau. Tau tangles can interfere with the way the brain receives signals. Researchers have said that they’re uncertain about the mechanisms that kickstart this process but know it can take years. Over time, however, the brain begins to shrink, which can lead to Alzheimer’s.

The Washington University team noted that some people have a genetic predisposition that leads them to smoke. As such, these people have a higher risk of reduced brain volume and of developing dementia or Alzheimer’s disease.

According to the World Health Organization, in 2020, 22.3 percent of the world’s population used tobacco. Tobacco use kills more than 8 million each year, including 1.3 million nonsmokers exposed to secondhand smoke.