Scientists at the University of Pennsylvania have shown that smoking can cause the brain to shrink, potentially linked to an increased risk of dementia. The study was published in the medRxiv preprint catalog and was considered preliminary until published in a peer-reviewed journal.
Previous studies have shown that smokers tend to have smaller brain volumes than non-smokers. But it was not clear whether smoking causes a reduction in brain size or whether people with smaller brains are more likely to smoke. In the new study, scientists presented convincing evidence that smoking causes brain shrinkage.
More than 28,000 people participated in the large-scale study. The scientists analyzed MRI images from the British Biobank, a large repository of UK residents’ genetic and medical data.
The researchers found that smokers have, on average, smaller brain volumes than non-smokers. Also, each additional pack smoked per year was associated with a reduction in gray matter volume of approximately 0.15 cc. This dose-response relationship supports the idea that smoking causally shrinks the brain.
Further analysis showed that people who quit long ago had slightly more gray matter in their brains than those who quit recently. This suggests that smoking cessation may somewhat reverse the decline in brain volume. For example, quitting smoking one year ago was associated with an additional 0.09 cc increase in gray matter volume. See those who have smoked daily in the past.
Decreased brain size is associated with neurological diseases, including Alzheimer’s disease. The scientists’ results suggest that smoking can directly increase the risk of developing dementia.