Investigating the bidirectional association between alcohol use and suicidal thoughts and behaviors in a population from the United States.

BACKGROUND: The association between alcohol problems and suicidal thoughts and behaviors (STB) is well documented, with recent evidence suggesting a causal effect of alcohol. Nevertheless, it is unclear if this relationship extends to less severe alcohol phenotypes. Moreover, only a few studies have explored whether STB may also increase alcohol use/problems. In this study, we combined two complementary methods to improve causal inference and investigate the bidirectional associations between alcohol use and STB. METHODS: We used the National Longitudinal Study of Adolescent to Adult Health (Add Health) with information on alcohol use and suicide ideation and attempts across five waves of data (age ranges: 10-43). First, we fit a cross-lagged panel model using data from Waves I-V to test the bidirectional associations between alcohol use and suicide ideation/attempt. This model advances causal knowledge by leveraging longitudinal data and controlling for unmeasured confounders related to both alcohol use and STB. Data from 17,908 unrelated participants were included in the model. Second, we included data from cousins, half-siblings, full siblings, and monozygotic (MZ) twin pairs to perform co-relative analyses, enhancing causal inference by controlling for unmeasured genetic and familial confounders. RESULTS: Cross-lagged findings showed small positive associations from suicide ideation to alcohol use (βs = 0.045-0.050) and from alcohol use to suicide ideation (β = 0.064) during adolescence/early adulthood in females. In males, results indicated one significant association between alcohol use in late adolescence and suicide attempt in adulthood (β = 0.508). Co-relative analyses revealed small but significant associations between alcohol use and STB in full siblings (OR = 1.41), but results in MZ twins were mostly inconclusive due to a lack of power. CONCLUSION: Our results suggest complex and potentially bidirectional associations between alcohol and suicide phenotypes, but do not provide strong evidence for a causal pathway.