All-cause and External-cause Mortality by Sexual Orientation before and after Marriage Equality: A nationwide cohort study in Australia
Melbourne Institute Working Paper No. ia/ca
Date: October 2025
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Abstract
Background: Sexual minorities face elevated risk of premature mortality, particularly from external causes such as suicide. Recent improvements in societal attitudes and legal rights pertaining to sexual minorities, including same-sex marriage legalisation, has been linked to improved mental health among sexual minorities. Despite these dramatic shifts, few studies have examined secular trends in all-cause and external-cause mortality by sexual orientation. Methods: Using Australian 2011 Census data linked to mortality records (2011–2023), a retrospective cohort analysis was undertaken for all adults identified in same-sex relationships and a 5% random sample of adults in different-sex relationships. Cox proportional hazard models were used to estimate all-cause and external-cause mortality risk by sexual orientation, while adjusting for demographic confounders. Results were additionally stratified into periods before and after Australia’s 2017 legalisation of same-sex marriage. Findings: The study cohort included 885,315 individuals, including 26,644 females in same-sex relationships and 27,885 males in same-sex relationships (mean follow-up 12.2 and 12.1 years, respectively). During follow-up, compared to those in different-sex relationships, males in same-sex relationships experienced elevated risk of all-cause mortality [HR1.17 (95% CI 1.07;1.27)], whereas no excess was observed among females in same-sex relationships [(HR 1.04 (95%CI 0.91;1.12)]. External-cause mortality was elevated for both females and males in same-sex relationships [HR1.90 (95%CI 1.55;2.32) and HR2.75 (95%CI 2.06;3.67), respectively]. Among females in same-sex relationships, external-cause mortality risk was similar in the periods before and after marriage equality [HR1.95 (95%CI 1.44;2.64) and HR1.86 (95%CI 1.42;2.43) respectively]; among males in same-sex relationships, it declined from HR3.50 (95% CI 2.31;5.29) to HR2.24 (95% CI 1.50;3.35). Interpretation: Although external-cause mortality risk among sexual minorities has declined since marriage equality in Australia, it remains significantly higher than individuals in different-sex relationships. These results suggest the need for policy action and enhanced protections for sexual minorities.
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