Objective A high body mass index (BMI) is associated with an increased risk for severe liver disease. It is unclear if this risk differs across BMI categories, and if the association is partially attributed to development of type 2 diabetes mellitus (T2DM).

Design We used register data from more than 1.2 million Swedish men enlisted for conscription between 1969 and 1996. Data regarding new events of severe liver disease and T2DM during follow-up were obtained by record-linkage of population-based registers. We used Cox regression to estimate adjusted HRs for future inpatient care and mortality in severe liver disease and incidence of hepatocellular carcinoma (HCC) across BMI categories, using BMI of 18.5–22.5 kg/m² as reference.

Results During a follow-up of more than 34 million person-years, 5281 cases of severe liver disease including 251 cases of HCC were identified. An association with severe liver disease was found for overweight (HR 1.49, 95% CI 1.35 to 1.64) and for obese men (HR 2.17, 95% CI 1.82 to 2.59). Development of T2DM further increased the risk for severe liver disease across all BMI categories, for instance, men with obesity and T2DM had a higher risk of severe liver disease (HR 3.28, 95% CI 2.27 to 4.74) than men with obesity free of T2DM (HR 1.72, 95% CI 1.72 to 2.54).

Conclusions A high BMI in late adolescent men was associated with an increased risk of future severe liver disease, including HCC. Development of T2DM during follow-up was associated with a further increased risk of severe liver disease, independent of baseline BMI.