Epidemiology of undiagnosed depression in people with diabetes mellitus: a comparative analysis of Ireland, England and the USA

Objectives Improving detection of depression in people with diabetes is recommended. However, little is known about how different health systems compare in depression detection. We estimated and compared the (1) prevalence of depression detection in people with and without diabetes, and (2) association between diabetes and undiagnosed depression across three health systems. Design Cross-sectional analysis of three nationally representative studies: The Irish Longitudinal Study on Ageing, the English Longitudinal Study on Ageing and the Health and Retirement Study. Setting Community-dwelling adults in Ireland, England and the USA. Participants Adults aged >= 50 years. Primary and secondary outcome measures The primary outcome was depression diagnosis. The secondary outcome was any depression. Any depression was defined by the presence of self-reported doctor-diagnosed depression or current depression symptoms on the Centre for Epidemiological Studies-Depression scale. Depression diagnosis was categorised as: undiagnosed, symptomatic and diagnosed, and asymptomatic and diagnosed. We estimated age-standardised prevalence of depression diagnosis by country and diabetes status. Anyone who self-reported having ever received a doctor diagnosis of diabetes was classified as having diabetes. Among respondents with depression, we estimated the association between diabetes and undiagnosed depression by country using multivariable logistic regression. Results The prevalence of depression (diagnosed and undiagnosed) was higher in people with diabetes in each country with absolute rates varying by country; undiagnosed prevalence (Ireland: diabetes 10.1% (95% CI 7.5% to 12.8%) vs no diabetes 7.5% (95% CI 6.8% to 8.2%), England: diabetes 19.3% (95% CI 16.5% to 22.2%) vs no diabetes 11.8% (95% CI 11.0% to 12.6%), USA: diabetes 7.4% (95% CI 6.4% to 8.4%) vs no diabetes 6.1% (95% CI 5.7% to 6.6%)). In the fully adjusted model, there was no clear pattern of association between diabetes status and undiagnosed depression; Ireland: OR=0.82 (95% CI 0.5 to 1.3), England: OR=1.47 (95% CI 1.0 to 2.1), USA: OR=0.80 (95% CI 0.7 to 1.0). Conclusions Although undiagnosed depression was more prevalent among people with diabetes, the relationship between diabetes and undiagnosed depression differed by country. Targeted efforts are needed to improve depression detection among community-dwelling older adults, particularly those with diabetes.