Diabetes and undiagnosed depression in the over 50s in Ireland, England and the USA, by Niamh McGrath

Diabetes is estimated as posing a 24 – 33% increased risk of new depression cases (1,2). This is thought due to shared underlying biological mechanisms (3–6) as well as the psychosocial burden of living with diabetes, due to unhelpful cognitions and beliefs related to diabetes (7) and/or poor access to and availability of quality diabetes care (8). Depression among people with diabetes is associated with increased risk of diabetes-related complications (9), mortality (10), and costs to health systems (11). As such, many evidence-based diabetes care recommendations include strategies for timely diagnosis and management (12–15).

However, the burden of undiagnosed depression remains poorly understood. In general populations, approximately 42-45% of people with depression go undiagnosed (16). A similar proportion (approximately 45%) has been reported as going undiagnosed among people with diabetes in the USA (17) though diabetes has also been associated with increased odds of diagnosed and treated (versus undiagnosed and untreated) depression in the USA (18). Examining undiagnosed depression in people with diabetes outside of the USA is important given the lack of available data and the role of health system factors such as health system financing in influencing depression diagnosis and treatment (17,19,20).

Our paper, recently published in BMJ Open, used nationally representative general population datasets to explore disparities in undiagnosed depression between adults aged 50 years and older with and without diabetes. Specifically, we compared the prevalence of depression detection i.e. undiagnosed, diagnosed and symptomatic and diagnosed and asymptomatic in community dwelling adults with and without diabetes and the association between diabetes and undiagnosed (versus diagnosed) depression across three health systems (Ireland, England and the USA).

We found more cases of depression (diagnosed and undiagnosed) in people with diabetes in each country with absolute rates varying by country. In Ireland and in England, most depression cases were undiagnosed. The prevalence of undiagnosed was; 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%)). The relationship between diabetes and undiagnosed (versus diagnosed) depression differed across health systems with more undiagnosed depression in people with diabetes than without diabetes in England (OR=1.51, 95% CI 1.1 to 2.2) and less undiagnosed depression in people with diabetes than without diabetes in Ireland and the USA (OR=0.84, 95% CI 0.5 to 1.3 and OR=0.79, 95% CI 0.7 to 1.0 respectively).

We drew three conclusions from this work. First, depression is common in older adults and more so in those with than without diabetes. Second, the size of the problem of undiagnosed depression differs across countries. Taken together, the findings support the need for targeted efforts to improve detection of depression among older adults, particularly among those with diabetes. Our related research explored implementation of depression screening as part of diabetes care (published paper available here) and how to implement depression screening as part of routine type 2 diabetes care in Ireland (in preparation).

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Niamh McGrath is a Research Officer at the Health Research Board Evidence Centre. Niamh is a SPHeRE Scholar. Her PhD thesis titled “Recognising Emotional Aspects of Diabetes (READ) Study: Understanding detection of diabetes distress and depression in people with type 2 diabetes mellitus in community setting” was undertaken at University College Cork and supervised by Prof Patricia Kearney, Dr Sheena McHugh and Dr Elaine Toomey.