Not long ago, people who discussed the connection between the mind and body were labeled as new age quacks and the observations they made were largely considered unscientific, not evidence-based, and unsubstantiated by peer-reviewed research. When asked about any connection between depression and physical health or disease, most medical experts would say something along the lines of “It’s possible, but there’s no real evidence for that yet.”
Slowly, however, members of the scientific and medical community have accepted the reality of the mind-body connection. Or, more importantly, the reality of the connection between emotions and the body.
We’re relieved the scientific community finally caught up with and accepted these connections, because for many of us, they’ve always been obvious.
When thinking about the mind-body or emotion-body connection, we can offer several simple examples that we all understand from personal experience. For instance:
- When we think about something we look forward to, we often experience a physical sensation of anticipation.
- When we think about something in the future we dread, we often experience a physical sensation of fear.
- If we’re hungry, we can get angry, frustrated, and irrational.
- After we eat, we often feel a sense of contentment or pleasure.
Those things are patently obvious to everyone. Obvious, yes: then why, for years, was the connection between our thoughts and our bodies, and the connection between our bodies and our emotions, considered a woo-woo new-agey concept that had no place in modern medical practice?
Because clearly, our thoughts and emotions can affect our bodies, our bodies can affect our thoughts and emotions.
One reason is that some people on the mind-body connection side of the argument did make unsubstantiated claims. It was easy to find claims like harboring resentment will cause cancer and back pain is the result of unresolved trauma. While it’s true that there may be associations between trauma and physical ailments, and repressed emotions and chronic disease, real evidence does not support claims like these.
However, a recent study takes an important step forward: it examines the association between depression and physical disease that results in hospitalization.
Depression and Physical Disease: Evidence-Based Associations
Published in May 2023, the paper “Association Between Depression and Physical Conditions Requiring Hospitalization” addresses a simple question:
What are the most common conditions requiring hospital treatment in people with depression?
The research team recognized that mental health disorders are a major contributor to disease in higher-income countries, with depressive disorders recognized as one of the primary causes of disability worldwide. That’s why they initiated their research effort. Depression is a prevalent condition worldwide, but there’s a lack of quality, evidence-based research on the association of depression with physical disease. In addition, the research team recognized that while depression is rarely considered a risk factor for physical disease, it might be an important risk factor diagnosing physicians have missed for decades.
While there is a lack of research, some descriptive studies exist on comorbid depression and physical conditions. Comorbid means the presence of two clinical diagnoses at the same time. Previous research shows the following prevalence rates of depression among people with severe or chronic physical disease, or the comorbidity of depression and severe or chronic physical disease:
- Myocardial infarction: 29%
- Type 2 diabetes: 28%
- Parkinson disease: 23%
- Stroke: 18%
- Cancer: 16%
- Alzheimer disease: 13%
Additional evidence suggests depression may be a risk factor for and exacerbate the progression of some physical illnesses. It’s also important to note that some previous research suggests a bidirectional association between depression and coronary heart disease, stroke, and diabetes. This means that when a person has both depression and one of these physical diseases, each condition can act as a risk factor for and exacerbate the disease progression of the other.
We’ll be clear: the research team did not try to prove claims such as depression causes cancer or anger gives you ulcers.*
Instead, this research lays the foundation for incorporating mental health factors into the clinical screening for physical disease.
Before we look at the results of this study, we’ll quickly review the prevalence rates of depression in the U.S.
Depression in the U.S.: Facts and Figures
Here are the latest statistics on depression in the U.S., as published in the 2021 National Survey on Drug Use and Health (2021 NSDUH):
Major Depressive Episode (MDE):
- Adults 18+: 8.3% (21.0 million)
- 18-25: 18.6% (6.2 million)
- 26-49: 9.3% (9.5 million)
- 50+: 4.5% (5.3 million)
- 65+: 2.8% (1.5 million)
MDE With Severe Impairment
- Adults 18+: 5.7% (14.5 million)
- 18-25: 13.3% (4.4 million)
- 26-49: 6.5% (6.6 million)
- 50+: 2.9% (3.4 million)
- 65+: 1.3% (739,000)
What these prevalence rates tell us is that millions of people in the U.S. have a mental health condition – a depressive disorder – that may increase their risk of developing various serious physical diseases. However – and we repeat – when physicians in primary care or specialists clinics screen for physical disorders, most do not ask about mental health conditions, and most do not understand that a mental health disorder such as depression may be a significant risk factor for physical disease.
Let’s take a look at the study and the results and answer the question we pose in the title of this article:
What’s the connection between depression and physical disease?
Depression and Physical Disease Requiring Hospital Visits
To determine the association of depression and physical disease that requires hospitalization, researchers accessed two large databases and tracked information on specific patients from their hospital visit to a follow-up point after five years. They retrieved data from the UK Biobank and two cohorts of patients from large scale public studies conducted in Finland: the Health and Social Support Study (HeSSup) and the Finnish Public Sector Study (FPS)
Here’s a breakdown of the study participants:
- 130,652 patients
- Average age: 63
- 45% male
- 55% female
- Presence of depression:
- Mild: 18%
- Severe: 2%
- None: 80%
- 109,781 patients
- Average age: 42
- 21% male
- 79% female
- Presence of depression: 99%
We’ll point out four things about this sample set:
- It’s large enough to make population level generalizations, with a total of 240,433 patients.
- It represents male and female patients.
- It includes people from age 31 to age 71, a range that allows for generalization to the adult and older adult demographic.
- The set includes people hospitalized for depression – the Finnish cohorts – and people hospitalized for physical disease – the UKBiobank patients.
In the UK patients, researchers assessed depression at baseline with a 9-item Patient Health Questionnaire (PHQ-9), and in Finnish patients, with available physician diagnoses and hospital records on admissions for depression. Researchers assessed depression at five-year follow up using electronic records available from the British National Health Service (NHS) and the Finnish HeSS and FDS studies.
Let’s take a look at what they found.
Depression and Physical Disease: The Results
The goal of the study was to identify the most common conditions requiring hospital treatment in people with depression. The top-line results showed that depression was associated with at least 29 nonoverlapping conditions requiring hospital treatment at five-year post-baseline follow-up. Please note that in the results that follow, subgroups of conditions do not appear separately. Therefore, the total number of conditions reported below may not total 29.
These conditions most associated with depression included:
- Hazard ratio (HR) of 5.97
- A person with a sleep disorder is 497% more likely to have depression than a person without a sleep disorder
- HR: 5.15
- 415% more likely to have depression
Ischemic heart disease:
- HR: 1.76
- 76% more likely to have depression
Chronic obstructive bronchitis:
- HR: 4.11
- 311% more likely to have depression
- HR: 2.52
- 152% more likely to have depression
- HR: 3.99
- 299% more likely to have depression
- HR: 1.80
- 80% more likely to have depression
The highest rates of depression were observed among people with:
Endocrine disease/related internal organ disease:
- Incidence rate: 245 per 1000 people with depression
- A person with depression has 9.8% increased risk of developing endocrine/related organ disease requiring hospitalization, compared to a person without depression
- Incidence rate: 91 per 1000 people
- A person with depression has a 3.7% increased risk of developing musculoskeletal disease requiring hospitalization, compared to a person without depression.
Circulatory system/blood diseases:
- 86 per 1000 people
- A person with depression has 3.9% increased risk of developing a circulatory system/blood disease requiring hospitalization, compared to a person without depression
One small subset of data from this section of the study showed the following:
Hospital-treated mental, behavioral, and neurological disorders:
- Incidence rate: 20 per 1000 people
- A person with depression has a 1.7% increased risk of developing a mental, behavioral, or neurological disorder requiring hospitalization, compared to a person without depression
Finally, researchers identified a bidirectional relationship between depression and 12 diseases or conditions. Reminder: in this context, bidirectional means the presence of these diseases can exacerbate the course of a depressive disorder, and the presence of depression can likewise exacerbate the course of these diseases. Researchers identified bidirectional relationships between depression and the following diseases/conditions:
- Digestive/abdominal pain
- Digestive system diseases
- Mood disorders
- Sleep disorders
- Soft tissue disorders
- Circulatory disorders
- Respiratory disorders
- Bacterial infections
That’s the data. What it shows us, and also shows clinicians, is reliable evidence they need to know when screening for various physical diseases. We’ll present this information in the words of the study authors themselves:
“The findings of this multicohort study suggest that, compared with individuals without depression, those with self-reported severe or moderately severe depression have at least a 1.5-times higher risk of 29 nonoverlapping conditions across multiple organ systems.”
We’ll discuss these results now, and share potential explanations for these relationships identified by the research team.
Mind, Body, Emotion: Connections Can Help Diagnose and Assess Risk
In the past, identifying a mental health disorder such as depression as a risk factor for a physical disorder – an endocrine disease, for instance – would have been met with indifference most likely tinged with scorn and disdain. That’s because we did not fully understand the connection between mental and emotional states and disease states. We still don’t understand the mechanisms of connection completely – i.e. how depression increases risk of endocrine disease, for instance – but we have taken an important step forward in recognizing the connections exist.
This study gives us one of our first large-scale meta-analyses of the relationship between depression and physical disease. Here’s more from the research team:
“Overall, our findings emphasize the important role of depression as a risk factor for physical illnesses* requiring hospital treatment.”
While this study does not explore or offer scientific, peer-reviewed evidence for the mechanisms by which depression can increase risk for physical diseases, they do offer potential explanations. They hypothesize that a person with depression may reduce their overall activity, self-isolate, and live a sedentary lifestyle: this could account for instances of obesity, diabetes, or other conditions associated with a lack of physical activity.
Further, they hypothesize that a person with depression may self-medicate with alcohol and engage in chronic alcohol use, which is associated with liver disease, kidney disease, and other serious physical complications.
Finally, they point out the association between long-term cigarette smoking and depression, and observe that cigarette smoking is associated with various respiratory and circulatory system diseases (lung and heart) diseases.
Those connections are logical, and that’s what we mean when we say the mind-body connection – and by extension, the emotion-body connection – is not a new-agey woo-woo concept. It’s very real, and this study presents a robust evidence base to support it. We’re confident that – with research like this publicly available – clinicians at all levels of care will consider mental health disorders as potential risk factors when screening for various physical diseases and conditions.