Family background may explain much of the mental health gap tied to sexual orientation, twin studies suggest

A recent study suggests that a significant portion of the mental health differences between non-heterosexual and heterosexual individuals may be linked to shared family background. When comparing non-heterosexual individuals to their heterosexual siblings and twins, the mental health gap decreased by approximately half, and by about two-thirds among identical twins. The findings were published in Psychological Medicine.

According to the most common explanation, Sexual Minority Stress Theory, the mental health gap can be attributed to the higher levels of social stress faced by sexual minorities, such as discrimination, bullying, and systemic stigma. However, this study suggests that shared family genetics and upbringing might also play a major role in these disparities.

The research, led by Péter Przemyslaw Ujma of Semmelweis University, aimed to determine whether the association between sexual orientation and mental health is primarily due to family factors. Genetically informed studies, which compare non-heterosexual individuals with their own heterosexual siblings, have produced conflicting results on whether mental health disparities stem from minority stress or shared family genetics and upbringing.

To address this uncertainty, Ujma and his colleagues conducted a comprehensive analysis of 17 English-language studies involving twins and non-twin siblings who reported their sexual orientation and mental health. They examined three types of comparisons: the general population gap, comparisons between heterosexual and non-heterosexual individuals across various family members, and direct comparisons between identical twins where one twin was heterosexual and the other was not.

The results showed that the mental health disparity decreased as genetic and family relatedness increased. In the general population, non-heterosexual individuals had worse mental health by about 0.41 standard deviations. However, when controlling for family relationships, the mental health gap was reduced by 47.5 percent. Identical twins, who share nearly 100 percent of their genes and typically experience the same early upbringing, provided the most rigorous test for family-level factors.

Comparing a non-heterosexual individual to their identical heterosexual twin reduced the mental health gap by 65.7 percent, although the difference between this estimate and the family members comparison was not statistically significant.

The authors interpret these findings as evidence that roughly two-thirds of the mental health gap in the population can be attributed to familial factors, such as shared genes and upbringing, rather than minority stress alone. Even with the inclusion of a large Swedish sibling study, the estimated reduction in the gap remained at 27.8 percent for family members overall and 53.7 percent for identical twins.

The authors still suggest that sexual minority stress could be a contributing factor for the remaining disparity, alongside other possible explanations, such as differences in life paths between non-heterosexual and heterosexual individuals.