The epidemiology of UK autoimmune liver disease varies with geographic latitude.

Abstract Background & aims The epidemiology of autoimmune liver disease (AILD) is challenging to study because of the diseases’ rarity and because of cohort selection bias. Increased incidence further from the Equator is reported for multiple sclerosis, another autoimmune disease. We assessed the incidence of primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC), and autoimmune hepatitis (AIH) in relation to latitude. Methods Retrospective cohort study using anonymised UK primary care records 2002-01-01 to 2016-05-10. All adults without a baseline diagnosis of AILD were included and followed until first occurrence of an AILD diagnosis, death, or they left the database. Latitude was measured as registered general practice rounded down to whole degrees. Results The cohort included 8,590,421 records with 53.3×107 years follow-up from 694 practices. There were 1314 incident cases of PBC, 396 of PSC, and 1034 of AIH. Crude incidences (95% confidence interval) was: PBC 2.47 (2.34–2.60), PSC 0.74 (0.67–0.82), and AIH 1.94 (1.83–2.06)/100 000/year. PBC incidence correlated with female sex, smoking, and deprivation; PSC incidence correlated with male sex and non-smoking; AIH incidence correlated with female sex and deprivation. More northerly latitude was strongly associated with incidence of PBC: 2.16 (1.79–2.60) to 4.86 (3.93–6.00) from 50-57°N (P=.002) and AIH 2.00 (1.65–2.43) to 3.28 (2.53–4.24)(P=.003), but not PSC 0.82 (0.60–1.11) to 1.02 (0.64–1.61)(P=.473). Incidence after adjustment for age, sex, smoking, and deprivation status showed similar positive correlations for PBC and AIH with latitude, but not PSC. Incident AIH cases were younger at greater latitude. Conclusions In the UK we describe an association between increased latitude and the incidence of PBC and AIH that requires both confirmation and explanation.