Smoking and Cognitive Performance: The Chicken and Egg Problem

To the Editor: In the November 2018 issue of the Journal, Vermeulen et al. (1) presented an interesting comparison of cognitive performance in smokers and nonsmokers (nonsmokers did better), and in smokers with psychosis who did and did not manage to stop smoking (quitters had a better score in one subtest at follow-up). However, the authors’ conclusion that smoking cessation may improve processing speed, and the accompanying editorial (2) that goes much further and asserts that the study shows that smoking has adverse effects on, and that stopping smoking leads to a rapid recovery of, cognitive performance, may be an overinterpretation of the findings.

Adolescents with lower education and socioeconomic status are more likely to become smokers (3, 4), and it is possible that the lower cognitive performance in smokers in this sample was not caused by smoking, but preceded it. Regarding the finding that patients who achieved smoking abstinence had faster processing speed at follow-up, it is likely that patients who are in good remission are more likely to stop smoking than those who are not, and that it is the remission, rather than smoking cessation, that is accompanied by cognitive improvement (especially as it is usually also accompanied by reduced medication that the yes/no medication variable that was controlled for may not capture). This interpretation is supported by the fact that such improvements were not seen in the other cohorts in this study.

Rather than concluding that smoking impairs and that stopping smoking improves cognitive performance, a possibility needs to be considered that the results simply confirm that people who find smoking rewarding differ from those who do not and that patients in good remission are more likely to stop smoking than those whose health status and medication levels have not changed.