Same-sex marriage, autoimmune thyroid gland dysfunction and other autoimmune diseases in Denmark 1989–2008

Autoimmune diseases have been little studied in gay men and lesbians. We followed 4.4 million Danes, including 9,615 same-sex married (SSM) persons, for 47 autoimmune diseases in the National Patient Registry between 1989 and 2008. Poisson regression analyses provided first hospitalization rate ratios (RRs) comparing rates between SSM individuals and persons in other marital status categories. SSM individuals experienced no unusual overall risk of autoimmune diseases. However, the risk of autoimmune thyroid dysfunction was increased, notably Hashimoto's thyroiditis (women(SSM), RR = 2.92; 95% confidence interval (CI) 1.74-4.55) and Graves' disease (men(SSM), RR = 1.88; 95% CI 1.08-3.01). There was also an excess of primary biliary cirrhosis (women(SSM), RR = 4.09; 95% CI 1.01-10.7), and of psoriasis (men(SSM), RR = 2.48; 95% CI 1.77-3.36), rheumatic fever (men(SSM), RR = 7.55; 95% CI 1.87-19.8), myasthenia gravis (men(SSM), RR = 5.51; 95% CI 1.36-14.4), localized scleroderma (men(SSM), RR = 7.16; 95% CI 1.18-22.6) and pemphigoid (men(SSM), RR = 6.56; 95% CI 1.08-20.6), while Dupuytren's contracture was reduced (men(SSM), RR = 0.64; 95% CI 0.39-0.99). The excess of psoriasis was restricted to same-sex married men with HIV/AIDS (men(SSM), RR = 10.5; 95% CI 6.44-15.9), whereas Graves' disease occurred in excess only among same-sex married men without HIV/AIDS (men(SSM), RR = 1.99; 95% CI 1.12-3.22). Lesbians and immunologically competent gay men in same-sex marriage face no unusual overall risk of autoimmune diseases. However, the observed increased risk of thyroid dysfunction in these lesbians and gay men deserves further study.