Does Smoking Cause Lower Educational Attainment and General Cognitive Ability? Triangulation of causal evidence using multiple study designs

Suzanne H Gage*, Hannah M Sallis, Glenda Lassi, Robyn E Wootton, Claire Mokrysz, George Davey Smith, Marcus R Munafo

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

Background: Observational studies have found associations between smoking and both poorer cognitive ability and lower educational attainment; however, evaluating causality is challenging. We used two complementary methods to explore this. Methods: We conducted observational analyses of up to 12,004 participants in a cohort study (Study One) and Mendelian randomization (MR) analyses using summary and cohort data (Study Two). Outcome measures were cognitive ability at age 15 and educational attainment at age 16 (Study One), and educational attainment and fluid intelligence (Study Two). Results: Study One: heaviness of smoking at age 15 was associated with lower cognitive ability at age 15 and lower educational attainment at age 16. Adjustment for potential confounders partially attenuated findings (e.g., fully adjusted cognitive ability beta -0.736, 95% CI -1.238 to -0.233, P = 0.004; fully adjusted educational attainment beta -1.254, 95% CI -1.597 to -0.911, P < 0.001). Study Two: MR indicated that both smoking initiation and lifetime smoking predict lower educational attainment (e.g., smoking initiation to educational attainment inverse-variance weighted MR beta -0.197, 95% CI -0.223, -0.171, P = 1.78 x 10-49). Educational attainment results were robust to sensitivity analyses, while analyses of general cognitive ability were less so. Conclusion: We find some evidence of a causal effect of smoking on lower educational attainment, but not cognitive ability. Triangulation of evidence across observational and MR methods is a strength, but the genetic variants associated with smoking initiation may be pleiotropic, suggesting caution in interpreting these results. The nature of this pleiotropy warrants further study.
Original languageEnglish
JournalPsychological Medicine
Publication statusAccepted/In press - 3 Sep 2020

Structured keywords

  • Physical and Mental Health
  • Tobacco and Alcohol

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