Understanding the Mental Health–Diabetes Link: Insights from the Hub for Metabolic Psychiatry

20 Jun

Last week (9th-15th) June was Diabetes Awareness Week, a week dedicated to shining a spotlight on a condition that affects 4.3 million people in the UK and that can have a profound impact on both physical and mental health. In this blog, Caroline Jackson, Kelly Fleetwood and Sarah Wild, explore the link between severe mental illness and type 2 diabetes and share more about what they are doing to investigate this link as part of their research at the Hub for Metabolic Psychiatry.

Diabetes and mental health

The link between diabetes and mental health goes back to the 17th century when Thomas Willis suggested that diabetes could be cause by “lasting melancholy and various depressions.” Modern research has confirmed the complex links between type 2 diabetes and mental health. However, much of this research has tended to focus on depression, with other mental health conditions given far less attention.

What do we know about the links between severe mental illness and diabetes?

By analysing information collected during normal health care our research has provided new insights into the links between severe mental illness (including schizophrenia, bipolar disorder and major depression) and diabetes. We have shown that people with severe mental illness have about a two-fold higher risk of developing type 2 diabetes, and develop it earlier, than people without mental illness. Our work also showed that this difference in risk has, disappointingly, not changed over the past 20 years. Research from Scotland and other similar countries where health care is essentially free, indicates that people with mental illness have a higher chance of developing complications from diabetes, such as heart disease. The reasons for these disparities in diabetes occurrence and complications are complex and poorly understood. Whilst various factors such as medication for mental illness and other health conditions and body weight play a role, common metabolic causes are likely to be important.

A puzzling paradox

On a positive note, in contrast to countries where health care is not free, we find that in Scotland patients with severe mental illness and diabetes are more likely to receive annual checks on their blood pressure or blood sugar. It is a curious paradox that people with mental illness appear to have similar blood sugar and blood pressure control than people without diabetes, yet have a higher chance of complications of diabetes. More detailed study of changes in people’s health over time, including measures such as blood sugar and blood pressure, may shed light on the interplay between severe mental illness and conditions like diabetes and its complications.

Deeper investigation of metabolic health

Metabolic health refers to how well someone’s body processes fat and sugar from what they eat. We can measure metabolic health using measurements of blood pressure, blood sugar and body weight. In our work in the Metabolic Psychiatry Hub, we are using routinely collected health data from across the UK to investigate changes in these measurements in people with severe mental illness. We will look at how measures change over time from point of diagnosis of mental illness. This means we can identify different patterns of these markers of metabolic health over many years. These patterns will not be the same for everybody and so investigating the variation in these patterns is critical. We can look at how these patterns vary according to individual characteristics, such as sex, ethnicity, other health conditions and medication, including for treatment of mental illness. By looking at these patterns over decades, we hope to identify sub-groups of people with severe mental illness who are at a high risk of developing conditions such as diabetes in the future. This opens up opportunities for introducing earlier and tailored approaches to reducing risk.

Similarly, among people who have already been diagnosed with type 2 diabetes, we will investigate how metabolic markers change over time and how this change varies by patient characteristics. We can then identify how different metabolic patterns impact on likelihood of complications, such as heart disease. We can also look at how these changes in metabolic factors affect the chance of someone developing poor mental health for the first time, following diabetes diagnosis. Again, by identifying those people who are at a high-risk of undesirable metabolic changes over time, we can better target approaches that improve metabolic health. Ultimately, this work could lead to improved treatment of both mental health and physical health conditions, including diabetes.