Examining Common Reasons for Hospitalization Among Patients With Depression

Philipp Frank, PhD.
Philipp Frank, PhD.

Depression and physical illness closely interact, but experts are still working to unravel the exact dynamic that occurs between the two.

Depression Care360 connected with Philipp Frank, PhD, to learn more about his study “Association Between Depression and Physical Conditions Requiring Hospitalization” recently published in JAMA Psychiatry.

In Part 1 of this Q&A, Dr Frank explains what we currently know about the relationship between depression and physical illness as well as the study methods used to determine the most common reasons for hospitalization among people with depression.

Check out Part 2 of this Q&A here! For more expert insights on depression, visit Depression Care360.

Brionna Mendoza, Associate Digital Editor, Depression Care360: What prompted you and your colleagues to investigate the connection between depression and hospitalizations in people with depression?

Frank Philipp, PhD: Previous studies that aimed to understand the nature of the relationship between depression and physical illnesses have been typically framed around two theoretical models—the consequence model, which posits that depression may develop in response to psychological, biological, and social changes related to disease onset and progression; and the antecedent model, which suggests that depression itself may be a risk factor for the development of physical illness.

While psychological wellbeing may not always receive the attention it deserves in clinical practice, it is important to recognize that the link between depression and physical illness has long been established. Intuitively, it is perhaps not very surprising that a considerable body of literature shows that people with severe medical illnesses have an increased risk of developing depression (i.e., the consequence model). For example, people with cancer are at increased risk of depression compared with those without a cancer diagnosis. Concomitantly, and in support of the antecedent model, there is also some evidence suggesting that depression may act as a risk factor for the development of distinct physical illnesses. It has been shown that psychological distress, particularly if severe and chronic, may directly, and via behavioral changes, affect several systems of the body, such as our immune and cardiometabolic system.  

However, past research in this field has primarily focused on individual diseases or a small range of diseases. This narrow focus has hindered our understanding of the broader impact of depression on the risk of developing or being hospitalized for various physical illnesses. Additionally, these studies were often based on relatively small sample sizes, which makes any conclusions about the generalizability of results uncertain. A further question that has remained unanswered until our study is: 'What are the most common reasons for hospitalization among individuals with depression?'

Mendoza, Depression Care360: Please walk us through the study methods and the most significant findings.

Dr Frank: Our study used data from a large-scale, prospective cohort, the UK Biobank study, and the findings were corroborated using two independent Finnish cohorts, the Health and Social Support study and the Finnish Public Sector Study. In total, our study included data from over 240,000 individuals of varying ages and backgrounds. 

We investigated the association between depression and 77 different physical illnesses that required hospital treatment. Depression was primarily assessed through the Patient Health Questionnaire (PHQ-9), which is used in clinical practice and identifies depressive symptoms based on the widely used Diagnostic and Statistical Manual of Mental Disorders (DSM-5) criteria. We also considered other depression-related factors like the participants’ age, sex, ethnicity, education, smoking and drinking habits, and physical activity levels. Both physical diseases and mental health conditions that required hospitalization were identified through linkage to national hospital and mortality registries in the UK and Finland. We excluded participants with pre-existing conditions from the analysis to focus on incident hospital-treated illnesses, that is, the antecedent model.

Our statistical approach used to assess the relationship between depression and hospital-treated physical illness was based on Cox proportional hazards regression analysis. This time-to-event method is used to measure something called a 'hazard ratio' - which is a measure of relative risk. Think of it like a comparison. If the hazard ratio is 1.5, it means that people with depression are 1.5 times more likely to end up in hospital due to a certain physical illness compared with people who don't have depression. Now, imagine we have two equally sized groups of people: one group with depression and one without. If, for example, 100 people without depression ended up in hospital due to a certain illness, we would expect 150 people with depression (1.5 times more) to be hospitalized for the same reason.

In our study, we found that individuals with moderately severe or severe depression have at least a 1.5 times higher risk of being hospitalized due to 29 different conditions. Interestingly, in absolute terms individuals with depression were 7 times more likely to be hospitalized due to endocrine and related internal organ diseases, such as diabetes and obesity, than due to mental or behavioral disorders. 

We also investigated whether depression impacted the progression of heart disease and diabetes, and the potential bidirectional relationship between depression and physical illness, that is both the antecedent and the consequence model. 

There was evidence for a bidirectional relationship between depression and physical illness. Specifically, we found that people who were hospitalized due to poisonings; falls; diseases or symptoms of the circulatory, respiratory, digestive, and musculoskeletal systems; and severe infections were more likely to develop depression compared with individuals who had not been hospitalized due to these conditions.  

Furthermore, we found that depression was associated with more rapid disease progression in people with heart problems and diabetes.

Philipp Frank, PhD, is a Research Fellow in Psychiatric Epidemiology at the Division of Psychiatry, University College London (UCL). He holds a Bachelor of Liberal Arts and Sciences in Psychology from University College Maastricht (UCM) and obtained an MSc in Health Psychology and a PhD in Psychiatric Epidemiology from UCL. Dr Frank's research focuses on unravelling the interplay between psychosocial, behavioral, and biological factors in the emergence of common mental health problems, particularly depression and dementia.

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