Type 2 Diabetes Mellitus in People with Severe Mental Illness: Inequalities by Ethnicity and Age. Cross-sectional Analysis of 588 408 Records from the UK

Aims: To investigate whether the association of severe mental illness with Type 2 diabetes varies by ethnicity and age.

Methods: We conducted a cross-sectional analysis of data from an ethnically diverse sample of 588 408 individuals aged ≥18 years, registered to 98% of general practices (primary care) in London, UK. The outcome of interest was prevalent Type 2 diabetes.

Results: Relative to people without severe mental illness, the relative risk of Type 2 diabetes in people with severe mental illness was greatest in the youngest age groups. In the white British group the relative risks were 9.99 (95% CI 5.34, 18.69) in those aged 18-34 years, 2.89 (95% CI 2.43, 3.45) in those aged 35-54 years and 1.16 (95% CI 1.04, 1.30) in those aged ≥55 years, with similar trends across all ethnic minority groups. Additional adjustment for anti-psychotic prescriptions only marginally attenuated the associations. Assessment of estimated prevalence of Type 2 diabetes in severe mental illness by ethnicity (absolute measures of effect) indicated that the association between severe mental illness and Type 2 diabetes was more marked in ethnic minorities than in the white British group with severe mental illness, especially for Indian, Pakistani and Bangladeshi individuals with severe mental illness.

Conclusions: The relative risk of Type 2 diabetes is elevated in younger populations. Most associations persisted despite adjustment for anti-psychotic prescriptions. Ethnic minority groups had a higher prevalence of Type 2 diabetes in the presence of severe mental illness. Future research and policy, particularly with respect to screening and clinical care for Type 2 diabetes in populations with severe mental illness, should take these findings into account.