If you’re a smoker, I’ve got some (more) bad news for you – long term smoking thins the cerebral cortex, the outer layer of the brain, responsible among others for memory, perception and language. The good news is that if you quit smoking, then the effect is reversible.

The cerebral cortex is the outer layer
depicted in dark violet. Image via Wiki Commons.

The history of smoking can be dated to as early as 5000 BC, but it wasn’t until the 19th and 20th century that the practice became widespread throughout the globe. Today, smoking (mainly tobacco smoking) is practiced by some 1.1 billion people; in other words, every 1 in 3 adults in the world smokes. This is a huge issue, because smoking is known  to cause a number of major health issues (including lung cancer and cardiovascular diseases). Now, you can add another problem to that long list: smoking thins the cerebral cortex.

This study involved 244 male and 260 female subjects. While this is not the first study to look at the link between tobacco and cortical thickness, it’s 5 times bigger than previous studies. All of the subjects were examined as children in 1947 as part of the Scottish Mental Survey, and then reexamined in recent times.

“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,” says the study’s lead author Dr. Sherif Karama, assistant professor of psychiatry at McGill University, psychiatrist at the Douglas Mental Health University Institute and an affiliate of the Montreal Neurological Institute.

However, the recovery process is slow and incomplete. Even after quitting for 25 years, the cortex isn’t back to its full thickness, but the improvement is significant.

Annual per capita cigarette consumption rates. Gray countries have no data available. (Max Fisher / Washington Post)

It’s noteworthy that  the cortex tends to get thinner as you age as well, but smoking accelerates the process.

“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,” says Dr. Karama.

Journal Reference: S. Karama, S. Ducharme, J. Corley, F. Chouinard-Decorte, J.M. Starr, J.M. Wardlaw, M.E. Bastin, I.J. Deary. BTBD3 Controls Dendrite Orientation Toward Active Axons in Mammalian Neocortex.  Molecular Psychiatry, Published Online February 10 2015. doi: 10.1038/mp.2014.187