Background: This study aims to understand the mechanisms contributing to the elevated risk of depression among sexual minority older adults compared to heterosexuals. Specifically, the role of loneliness as a potential mediator is investigated to inform targeted interventions for preventing depression in sexual minority populations., Methods: Data from the English Longitudinal Study of Ageing, focusing on adults aged over 50, were analysed. Sexual orientation (sexual minority or heterosexual) and loneliness scores (UCLA scale) were assessed at wave six (2010-2011), while depressive symptoms (CESD) were assessed at wave seven (2013-14). Linear regression models and mediation analyses, using g-computation formula and adjusted for confounders, were conducted., Results: The sample included 6794 participants, with 478 (7.0 %) identifying as sexual minorities. After adjustments, sexual minorities scored higher on depressive symptoms at wave seven (mean difference): 0.23, 95 % CI 0.07 to 0.39) and loneliness at wave six (MD: 0.27, 95 % CI 0.08 to 0.46). Loneliness was positively associated with depressive symptoms (coefficient: 0.27, 95 % CI 0.26 to 0.29). In mediation analyses, loneliness explained 15 % of the association between sexual orientation and subsequent depressive symptoms., Limitations: The dataset used sexual behaviour rather than desire and identity, potentially skewing representation of sexual minorities. Additionally, transgender older adults were not included due to limited gender diversity reported within the ELSA dataset., Conclusions: Loneliness appears to be a significant modifiable mechanism contributing to the heightened risk of depressive symptoms in sexual minority older adults compared with their heterosexual counterparts., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to declare., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)