Cigarette smoke is composed of hundreds of toxic compounds that when inhaled can cause harm to nearly every organ system within your body and the body of people exposed to your second hand smoke. This includes heart disease, increased blood pressure, strokes, bronchitis and emphysema (COPD), decreased fertility in males, birth defects in pregnant females and their offspring, type 2 diabetes, cataracts, childhood asthma, oral cancer, skin cancer, bladder cancer, liver cancer, lung cancer, stomach cancer, the list goes on and on. What about the brain? Does smoking have any negative effects on the organ that makes you, you? There is evidence from research showing that smokers have worse cognitive function later in life, which is a risk factor for dementia and Alzheimer’s disease. A large analysis of a number of studies found that smokers had a greater risk of developing dementia and that up to 14% of Alzheimer’s cases are caused by smoking. A new study, published in the journal Molecular Psychiatry, shows that smokers also have to worry about their brains shrinking.
This is not the first study to find similar results, but it is by far the largest one to date. The study looked at the thickness of the brains cortex, or outer layer, by MRI in 504 patients who ranged in age from 71-74 years old. The brains cortex is important in most of our higher functions like language and complex thought. The surface area of the cortex in humans is often considered what makes us the complex analytical animals we are. The researchers found that people who were current smokers had significantly thinner cortex’s than those who never smoked in their life. They also found that people who were ex smokers had cortex thicknesses that were closer to those people who had never smoked. This suggests that people who quit smoking could regain some of the lost cortical thickness. In fact, this is what the data showed. The longer people had gone since their last cigarette, the more cortical tissue they had regained. Also, people who had quit earlier in life (more than 28 years since last cigarette) had a greater thickness than those who quit later in life (less than 28 years since last cigarette) who were comparable to those who were still smoking. Finally, it was also noted by the researchers that the longer or more someone smoked, the greater the loss in the cortex was. It is interesting to note that these results held true regardless of the age, gender or initial cognitive abilities of the subjects. The researchers were able to properly control for these variables because the subjects in this study all had an IQ test performed at the age of 11 for another study in 1947 as well as information about their disease history, blood pressure, cholesterol levels, alcohol consumption and depression scores. The researchers also had detailed information about the subjects prior smoking history.
Let’s explain why these results are interesting and important. Your brain, and most of the other organs in your body like your lungs and digestive tract, rely and a large surface area to perform their tasks. Human brains have lots of folds to increase the surface area. If the cortex of smokers is getting thinner, then the surface area is also shrinking and your brain cannot do as much or gets less efficient at doing it. As we age, our cortex gets thinner anyways and is likely a reason for the loss of memory as we age. In smokers however, this decline is accelerated and therefore the decline in memory and other brain functions we associate with aging will occur earlier in life. It is important to note that all is not lost. If you quit, especially earlier in life, then you can likely regain some of the thickness in your cortex. However, the longer you smoke, the worse the thinning gets.
While we don’t yet know how different amounts of cortical thinning affect the brains function and we also don’t know the mechanism for this loss of cortex thickness. It is likely to be atrophy, similar to the loss of muscle mass following periods of inactivity, however more work needs to be done to figure this out. It also needs to be determined if there are specific regions of the brain that are more affected than others. For example, are the memory forming or recall areas of the brain affected more drastically than other regions. The researchers also state that it would be beneficial to increase the number of subjects who were in the current smoking group as it was smaller than the other groups (36 people vs. over 200 people in the other groups). The results are striking enough to add decreasing brain size to the list of harmful effects of smoking, as if you needed another reason to quit.