A sweeping new synthesis of twin and sibling studies suggests that much of the mental health gap between non-heterosexual and heterosexual people may stem from shared family background rather than social stigma alone. The analysis, led by Péter Przemyslaw Ujma of Semmelweis University, finds that when non-heterosexual individuals are compared with their own heterosexual siblings and twins, the mental health difference shrinks significantly—by about half in general sibling and twin comparisons and by roughly two-thirds among identical twins. The work is published in Psychological Medicine.
For decades, researchers have documented higher rates of anxiety, depression and other mental health difficulties among gay, lesbian and bisexual people. The dominant explanation has been Sexual Minority Stress Theory, which attributes much of the disparity to stressors like discrimination, bullying and systemic stigma. Earlier studies have linked experiences such as victimisation to distress, including a 2023 PsyPost-covered study that found higher same-sex attraction associated with distress, partly explained by victimisation.
But the new study examines whether the association between sexual orientation and mental health might reflect familial causes—genetic and early environmental factors that influence both temperament and mental health—from birth. The researchers sought to test this possibility with a genetically informed design, noting that prior findings in this area have been mixed.
Historically, genetic and environmental explanations have yielded conflicting results. An early 1999 study of identical male twins reported that gay men still experienced higher suicidal thoughts than their heterosexual twins, suggesting family background could not fully explain the disparity. In contrast, a 2011 twin study found evidence that shared genetic and environmental factors partly accounted for higher rates of depression among non-heterosexual people. These divergent results prompted the current, systematic synthesis.
Ujma and colleagues conducted a systematic multilevel meta-analysis, combing English-language studies in which twins or non-twin siblings reported both sexual orientation and mental health. They identified 17 studies that met their criteria, setting aside one large Swedish sibling study because it measured sexual orientation via same-sex marriage and reported results in a different statistical format. The team extracted data to compute effect sizes representing the mental health gap between heterosexual and non-heterosexual participants and grouped them into three comparison types.
The first comparison looked at the general, unmatched population—heterosexual individuals versus non-heterosexual individuals without considering family ties. The second pooled all available family pairs, including non-twin siblings, fraternal twins and identical twins. The third isolated comparisons strictly between identical twin pairs where one twin was heterosexual and the other was not.
In the unmatched general population, non-heterosexual participants showed worse mental health by about 0.41 standard deviations. When researchers controlled for family relationship, the disparity was reduced by about 47.5 per cent.
Identical-twin comparisons produced the strongest reduction, with the gap dropping by 65.7 per cent. While this reduction was larger than that seen in broader family-group comparisons, the authors acknowledge that the difference between the two estimates was not statistically significant—partly because only a small number of studies reported strict identical-twin data.
Taken together, the authors interpret the results as indicating that roughly two-thirds of the population gap may reflect familial factors, such as shared genes and upbringing, rather than minority stress alone. When the Swedish study was included in the analysis (an approach the authors treated separately), the estimated reductions were smaller: 27.8 per cent for family members overall and 53.7 per cent for identical twins.
However, the identical-twin analysis also showed that the gap does not vanish entirely. Non-heterosexual identical twins still exhibited higher rates of mental health symptoms than their heterosexual twins, suggesting that roughly one-third of the disparity arises from factors the twins do not share. The authors describe sexual minority stress as one possible explanation for this remaining portion, alongside other factors such as differences in life trajectories. More broadly, they argue that much of the disparity has been wrongly attributed to minority stress and that their results partly challenge the theory.
“The key takeaway is that shared familial factors may account for a substantial portion of mental health disparities associated with sexual orientation,” said Yiwen Wang, an assistant professor of sociology at the University of Central Florida who was not involved in the research. “Accounting for familial background reduces these disparities but does not eliminate them. The study provides an important complement to the minority stress literature by highlighting familial sources of mental health disparities that have received comparatively less attention. I would view these findings as complicating, rather than overturning, minority stress theory.”
Wang added a caution: “One thing I would caution against is interpreting these findings as evidence that minority stress does not matter. Accounting for familial factors reduces the disparities, but it does not tell us exactly what mechanisms are responsible for that reduction. Importantly, a meaningful mental health disparity remains even among identical twins.”
The researchers also note several limitations. They detected borderline publication bias in the population estimates, and the studies varied widely in how they defined sexual orientation and which demographic groups were included. Mental health measures differed substantially between studies, making it difficult to draw conclusions about specific disorders such as anxiety or depression in particular populations.
“The genetically informed design is a notable strength, and the overall pattern is compelling,” Wang remarked. “I would be more cautious about the magnitude of the estimates and their causal interpretation, given substantial heterogeneity across studies and the relatively limited evidence from identical twin comparisons.”
Another limitation is that the analyses could not cleanly separate genetic causes from shared environmental causes. While the larger reduction among identical twins points toward genetic factors, the difference between the identical-twin and broader family estimates was not statistically significant.
Because identical twins who differ in sexual orientation are relatively rare, the sample sizes for those strict comparisons were small, yielding wider margins of error. The authors recommend future work using highly standardised clinical measures of mental health and prioritising data from both siblings and identical twins to sharpen the picture.
They also urge studies that combine genetically informed designs with direct, longitudinal measures of discrimination, stigma and other minority-stressors to better understand how family background and social experiences interact in shaping mental health.
The study, “How much is sexual minority stress confounded with familial causes? A systematic multilevel meta-analysis,” was authored by Péter Przemyslaw Ujma, John D. Haltigan, and J. Michael Bailey.
