Sexual orientation and health disparities
: investigating etiological mechanisms using genetically-sensitive designs

Student thesis: Doctoral ThesisDoctor of Philosophy


Higher indicators of adverse mental and sexual health (depressive and anxiety symptoms, and risky sexual behavior) among sexual minority (lesbian, gay or bisexual – LGB) compared to heterosexual individuals imply social inequalities which manifest as minority stress experiences. As contributory genetic and environmental influences have been further implicated in these disparities, this thesis used genetically-sensitive designs to investigate the extent to which underlying genetic and environmental factors influence sexual orientation and its relationships with adverse health indices.
Chapter 2 used a sample from the Finnish Genetics of Sexuality and Aggression (GSA) cohort to investigate whether childhood gender nonconformity (CGN) and early-life adversities (ELA) individually moderated the genetic and environmental influences on sexual orientation. This chapter found that the variance of sexual orientation significantly decreased as childhood gender nonconformity increased and this was due to moderation of the individual-specific environmental (E) influences on sexual orientation.
Using the same sample, chapter 3 further investigated CGN, ELA and poor parent-child relationships as individual moderators of the genetic and environmental influences on the relationships between sexual minority status, and depressive and anxiety symptoms. Higher CGN was associated with higher additive genetic (A) influences and decreasing E influences on these relationships.
Chapter 4 used a second GSA sample to determine whether sexual minority status was causally associated with psychological distress (higher depressive and anxiety symptoms) and risky sexual behavior (RSB) by applying a novel combination of twin modelling and Mendelian Randomization. Consistent with the minority stress framework, causal influences flowed from sexual minority status towards both outcomes. Secondary analyses indicated significant reverse causal paths from psychological distress and RSB towards sexual minority status, suggesting positive feedback between minority stress and adverse health outcomes.
Using the second GSA sample, chapter 5 investigated whether disparities in mental health indicators (depressive and anxiety symptoms and alcohol and tobacco use problems) mediated increased RSB among sexual minority compared to heterosexual participants. By comparing biometric genetic models, this chapter showed that mental health disparities partly explained increments in RSB among sexual minorities and that these relationships were not confounded by correlated A and E influences. This finding was replicated in chapter 6 by using a UK twin cohort and extended it by specifying psychosocial disparities (depressive and anxiety symptoms, ELA and intimate partner violence) and excessive substance use as separate mediators in a single model. Both mediators jointly explained a larger proportion of the higher RSB among sexual minorities and there was no confounding by correlated A and E influences.
The findings from this thesis highlight CGN as an important factor in understanding sexual minority status and the increased risk for mental health difficulties among sexual minorities. The relevance of existing theoretical frameworks and structural interventions was validated by demonstrating causal associations between sexual minority status and adverse mental and sexual health indices which were not confounded by correlated etiological influences. This thesis also raised the possibility that adverse health outcomes may reinforce sexuality-related social disparities.
Date of Award1 Aug 2021
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorFruhling Rijsdijk (Supervisor) & Patrick Jern (Supervisor)

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