A co-twin–control analysis of adolescent and young adult drinking effects on learning and memory

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Background and aims: Existing evidence for a link between alcohol use and memory impairments in adolescents and young adults is largely correlational. We aimed to determine whether associations between drinking and episodic memory were consistent with a causal effect of drinking or accounted for by familial factors confounding such associations. Because cannabis use is associated with a similar pattern of performance on episodic memory measures, we assessed whether any associations might be attributable to concurrent cannabis use. Design, setting and participants: Observational study of individuals aged approximately 20–29 years, comprising two independent population-based cohorts of twins. A co-twin–control design permitted an estimate of alcohol exposure effects free of shared genetic and environmental confounding influences. Significant associations were followed-up with twin-difference analyses. Propensity scores derived from measures collected at age 11 were used to adjust for unshared confounders. Participants in both cohorts were assessed from the age of 11 (n = 1251) under the auspices of the Minnesota Center for Twin and Family Research. Measurements: Regression analyses with cumulative alcohol use as the predictor of interest. Multiple measures of attention, learning and memory from a widely used episodic memory task constituted dependent variables. Findings: Drinking was associated with poorer attention (P ≤ 0.003) and learning (P ≤ 0.008). Results were similar across the two cohorts. The within-pair effect in twin-difference analyses was significant only for measures of learning (P-values ≤ 0.004). Results were not due to measured unshared confounders or cannabis use. Drinking in adolescence (to age 20) and early adulthood (between 20 and 29) exerted independent effects on learning. Conclusions: There appears to be a robust and specific association between drinking and learning that can be reproduced across cohorts, is not easily accounted for by confounding factors or concurrent cannabis use and is consistent with a causal influence of drinking.

Original languageEnglish (US)
Pages (from-to)1689-1699
Number of pages11
Issue number7
StatePublished - Jul 2021

Bibliographical note

Funding Information:
Work on this paper was supported by National Institute on Drug Abuse grants R37DA005147, R01DA036216 and K01DA03720 and National Institute on Alcohol Abuse and Alcoholism grants R37AA009367 and R21AA02969. We are grateful to Tasha Walvig for her gracious help in verifying some of the interview data used and to Gretchen Saunders for helpful discussions about bias in the co-twin-control design.

Publisher Copyright:
© 2020 Society for the Study of Addiction


  • Adolescence
  • alcohol
  • cannabis
  • co-twin–control
  • short-term memory
  • verbal learning


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