Department of Psychological Sciences, University of Liverpool, Liverpool, UK.
School of Psychological Science, University of Bristol, Bristol, UK.
Psychol Med. 2022 Jun;52(8):1578-1586. doi: 10.1017/S0033291720003402. Epub 2020 Oct 7.
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.
We conducted observational analyses of up to 12 004 participants in a cohort study (Study One) and Mendelian randomisation (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).
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 -0.736, 95% CI -1.238 to -0.233, = 0.004; fully adjusted educational attainment -1.254, 95% CI -1.597 to -0.911, < 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 -0.197, 95% CI -0.223 to -0.171, = 1.78 × 10). Educational attainment results were robust to sensitivity analyses, while analyses of general cognitive ability were less so.
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.
观察性研究发现，吸烟与认知能力下降和受教育程度降低都有关联；然而，评估因果关系具有挑战性。我们使用两种互补的方法来探索这个问题。
我们在一项队列研究（研究一）中对多达 12004 名参与者进行了观察性分析，并使用汇总和队列数据进行了孟德尔随机化（MR）分析（研究二）。研究一的结果测量是 15 岁时的认知能力和 16 岁时的受教育程度，研究二的结果测量是受教育程度和流体智力。
研究一：15 岁时吸烟的严重程度与 15 岁时认知能力较低和 16 岁时受教育程度较低有关。调整潜在混杂因素后，发现结果有所减弱（例如，完全调整后的认知能力 -0.736，95%CI-1.238 至-0.233， = 0.004；完全调整后的受教育程度 -1.254，95%CI-1.597 至-0.911， < 0.001）。研究二：MR 表明，吸烟开始和终生吸烟都预示着受教育程度较低（例如，吸烟开始到受教育程度的逆方差加权 MR -0.197，95%CI-0.223 至-0.171， = 1.78×10）。受教育程度的结果对敏感性分析具有稳健性，而对一般认知能力的分析则不那么稳健。
我们发现一些证据表明吸烟与较低的受教育程度之间存在因果关系，但与认知能力无关。观察性和 MR 方法的证据相互印证是一个优势，但与吸烟开始相关的遗传变异可能存在多效性，这表明在解释这些结果时需要谨慎。这种多效性的性质值得进一步研究。
