Unique versus shared associations of substance use disorders and behavioural addictions with major depression: a commonality analysis in a large sample of young Swiss men
Substance use disorders (SUDs) and behavioural addictions (BAs) are common among young men, and they tend to co-occur. In addition, they are associated with mental health problems. The aim of the study was to estimate how much of the variance of major depression severity (MDS) explained by BAs and SUDs is unique to each and shared between each pair of these addictive disorders, respectively within and between BAs and SUDs.
The sample were 5516 young Swiss men (mean age 25.5; SD=1.26) who completed a self-report questionnaire. We assessed alcohol, cannabis and tobacco use disorders, and illicit drug use, six behavioural addictions (to internet, gaming, smartphone, internet sex, gambling and work) and MDS. Commonality analysis was used to decompose the variance of MDS explained (R-squared) by SUDs and BAs into independent commonality coefficients of unique, shared within SUDs, shared within BAs, and shared between SUDs and BAs contributions.
Overall, the 10 addictions explained 27.7% [95%CI: 25.7%, 29.7%] of the variance of MDS. 12.2% [10.6%, 13.9%] were explained uniquely by behavioural addictions, 7.2% [5.9%, 8.6%] were shared within behavioural addictions, 4.4% [3.3%, 5.4%] were shared between SUDs and BAs, 1.9% [1.2%, 2.6%] were shared within SUDs, and 2.0% [1.2%, 2.7%] were explained uniquely by SUDs. The highest unique contributions were by work (8.4% [6.9%, 9.9%]), internet (1.9% [1.2%, 2.7%]) and gaming addiction (1.5% [0.9%, 2.3%]). The highest shared contributions were between internet and gaming addiction (2.1% [1.6%, 2.7%]), followed by internet and work addiction (0.7% [0.4%, 1.1%]) and the triple of internet, smartphone and work addiction (0.6% [0.4%, 0.8%]).
The 10 addictions measured in our study explained more than a quarter of the variance of MDS, but only about half of this variance explained was uniquely explained by individual addictions, while the other half was shared between addictions. A greater proportion was explained uniquely or shared within BAs compared with the proportion with relation to SUDs (unique to SUDs, shared within SUDs and shared between SUDs and BAs). The association between MDS and addictions was more strongly related to BAs (especially work, internet and gaming addiction) than to SUDs, and about half of the total contribution of SUDs to MDS was shared with behavioural addictions. In conclusion, the interplay of a broad range of addictions, particularly BAs, should be considered when investigating the link between SUDs and MDS.