Smoking mass-produced tobacco cigarettes really came into fashion about 100 years ago. In that amount of time, the scientific and medical community has learned an incredible amount about how cigarettes affect human health. While lung disease, hypertension, and oral disease are among the most talked about detriments of smoking, it doesn’t even begin to cover the number of ways cigarettes harm the body. A new open access paper published in Molecular Psychiatry by lead author Sherif Karama from McGill University reports how prolonged cigarette smoking appears to contribute to the thinning of the brain's cerebral cortex.
The cerebral cortex is the outer layer of the brain, and is critical to higher-order functions such as language, consciousness, and memory. These abilities generally decline as dementia sets in, which has a strong correlation with cigarette smoking. The cortex thins over time due to natural aging, but the current paper suggests that smoking exacerbates thinning, which might be leading to dementia. There have been other studies concerning the link between cortex thickness and smoking, but they have been fairly small.
Karama’s team used magnetic resonance imaging (MRI) to examine the cortical thickness of 260 females and 244 males, who were all about 73 years old at the time. Many of the individuals had participated in a 1947 mental health survey and underwent cognitive testing in Scotland, and those previous results were compared to data collected during the new testing. The test subjects were also asked about their smoking habits, and were sorted into groups of individuals who had never smoked, who had quit smoking, and who currently smoke. Ultimately, they found significant differences in the cortical thicknesses between the three groups, with current smokers having the thinnest cortices, and those who had never smoked having the thickest.
"We found that current and ex-smokers had, at age 73, many areas of thinner brain cortex than those that never smoked. Subjects who stopped smoking seem to partially recover their cortical thickness for each year without smoking," Karama said in a press release.
While it is encouraging that the cerebral cortex can be repaired over time, the growth is not enough to return it to non-smoker levels. Even among individuals who had stopped smoking 25 years prior, the thickness between their cortices and those who had never smoked were obvious. Though it does get better with time, it appears that smoking cigarettes inflicts permanent damage on the cerebral cortex, and could leave the individual more prone to developing dementia.
"Smokers should be informed that cigarettes could hasten the thinning of the brain's cortex, which could lead to cognitive deterioration. Cortical thinning seems to persist for many years after someone stops smoking," Karama concluded.
No mechanism has been identified in this phenomenon, but future studies may reveal a molecular cause, and may even offer a possible line of treatment. That is purely hypothetical at this stage, however, and it’s probably better to just not smoke rather than bank on a potential future treatment.