Daily smoking linked to smaller brains

Smoking daily may cause the brain to shrink in a dose-response manner, and quitting does not seem to reverse the brain volume loss, as reported in a study.

Brain imaging data from 32,094 UK Biobank participants showed that a history of daily smoking was strongly associated with decreased total brain volume (effect size, -3,360 mm³; p=2.85 × 10^-8) and total gray matter volume (effect size, -2,964 mm³; p=2.04 × 10^-16). Furthermore, participants with more pack-years-smoked had a greater decrease in brain volume. [Biol Psychiatry Glob Open Sci 2024;4:74-82]

When genetic predisposition to smoking was examined, a strong association emerged for history of daily smoking but only modest association for total gray matter volume. However, mediation analysis indicated that history of daily smoking completely explained the link between genetic predisposition to smoking and total gray matter volume. These findings, according to the investigators, provide additional evidence that smoking is negatively associated with the differences in brain volume.

“Up until recently, scientists have overlooked the effects of smoking on the brain, in part because we were focused on all the terrible effects of smoking on the lungs and the heart,” said senior study author Dr Laura Bierut, the Alumni Endowed Professor of Psychiatry at Washington University School of Medicine in St Louis, Missouri, US.

“But as we’ve started looking at the brain more closely, it’s become apparent that smoking is also really bad for your brain,” Bierut added.

Multiple studies have raised the alarm regarding the adverse effect of smoking extending into the brain, with smoking being implicated in dementia. People who smoke are likely to have gray and white matter deterioration, which may explain why 14 percent of global Alzheimer’s disease cases could be attributable to cigarette smoking. [JAMA Neurol 2022;79:584-591; Lancet Neurol 2014;13:788-794; Lancet 2020;396:413-446; Lancet Neurol 2011;10:819-828; Alzheimers Dement 2014;10(suppl):S122-S145]

“It sounds bad, and it is bad,” Bierut said. “A reduction in brain volume is consistent with increased ageing. This is important as our population gets older, because ageing and smoking are both risk factors for dementia.”

Bierut’s statement delivers a sobering wake-up call, given that the brain changes associated with smoking seemed to be irreversible. In the present study, brain scans of participants who had quit smoking years before showed that their brain volume remained permanently smaller than those of participants who had never smoked.

Nevertheless, first study author Yoonhoo Chang, a graduate student at Washington University School of Medicine in St. Louis, Missouri, US, remained hopeful.

“You can’t undo the damage that has already been done, but you can avoid causing further damage,” Chang said. “Smoking is a modifiable risk factor. There’s one thing you can change to stop ageing your brain and putting yourself at increased risk of dementia, and that’s to quit smoking.”