To answer this question more fully, it is helpful to consider both the features of depression as well as the meaning of various ways of conceptualizing depression as a mental disorder, illness, or disease.
Depression as a Systemic Disease
There is an increasing trend toward evidence supporting the theory of depression as a systemic disease. A systemic disease is one that affects the whole body rather than just a single body part or organ system. This differs from a localized disease that only affects a single part of the body. Definitions of mental and physical conditions may overlap more than researchers previously thought—such that the distinction between a disease of the mind and disease of the body is blurred. Could it be that depression, a condition that can be treated with psychotherapy, can have an influence on the physical body, and if so, what does that mean?
What the Research Says
Evidence to support depression as a systemic disease comes in the form of biological changes that are seen in patients with depression. Depression may cause inflammation. It can also affect neuroendocrine regulation, which impacts hormone production. Depression is linked with increased platelet activity, which is also a marker of cardiovascular disease and diabetes. Depression affects autonomic nervous system activity, which controls bodily functions like heart rate, breathing, and digestion. In addition, depression is a known risk factor for low bone density. In this way, it is possible to see how depression could have a relationship to conditions like heart disease and diabetes—the very diseases to which it is being compared. If depression is related to your immune response, how might that look? A meta-analysis conducted at the University of Granada and published in the Journal of Clinical Psychiatry examined changes in the bodies of depressed people based on 29 previously published studies. It was found that depression caused an imbalance in antioxidants and free radicals that can potentially damage the cells of the body, also referred to as oxidative stress. After these patients with depression received treatment, their levels of malondialdehyde (a biomarker indicating oxidative stress) went back down to healthy levels. In addition, it was shown that their levels of zinc and uric acid rose back to normal levels after treatment.
Physical Indicators of Depression
People with depression often complain of physical symptoms like:
Changes in appetite Fatigue Sleeping too much or too little Weight loss or weight gain
We also know that some medical conditions can lead to depressive symptoms, such as hypothyroidism.
What the Future Holds
There are advances needed in how we diagnose depression, beyond screening from a list of symptoms. In the not too distant future, people may even be able to receive a biomarker test for depression. A test like this would be able to check someone’s blood for oxidative stress markers, endocrine markers, inflammatory markers, and other biomarkers of depression to determine the severity of their condition. For other people, tests like this could potentially determine whether or not they are genetically at risk of developing depression. For now, experts are still debating whether or not calling depression a disease is beneficial. The bottom line is that it’s important to understand that depression involves both physical and mental changes to the body and mind.
Features of Depression
According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), depression is diagnosed when five or more of the following symptoms (summarized below) have been present in the same two-week period and represent a change from your previous functioning. At least one of the symptoms must be either depressed mood or loss of interest or pleasure. Others may include:
Depressed mood most of the day, nearly every day Markedly diminished interest or pleasure in all, or almost all, activities most of the day, nearly every day Significant weight loss or weight gain (without intentional dieting) or decrease or increase in appetite nearly every day Insomnia or hypersomnia nearly every day Psychomotor agitation or retardation nearly every day Fatigue or loss of energy nearly every day Feelings of worthlessness or excessive or inappropriate guilt nearly every day Diminished ability to think or concentrate, or indecisiveness nearly every day Recurrent thoughts of death or recurrent suicidal ideation
In addition, the symptoms must cause significant distress or impairment in daily life and not be attributed to another medical condition or the effects of substance use. For more mental health resources, see our National Helpline Database.
Definitions of Disorder, Illness, and Disease
Depression has been referred to as a mental disorder, mental illness, and a systemic disease. While there is certainly overlap between these terms, each has a unique definition that we can consider when trying to understand what exactly depression is.
Mental disorder is a term that refers to conditions that disrupt your normal mental functioning (just as a physical disorder would be one that disrupts your normal physical functioning). Examples of mental disorders are depression, anxiety disorders, and post-traumatic stress disorder (PTSD). Mental illness is a term that is used interchangeably with mental disorder. Historically, illness is a term that was used to refer to someone’s experience of a condition. For instance, whether or not your depression has been formally diagnosed, you will still experience the symptoms just as powerfully. Medical professionals might use the term illness to describe a patient’s condition when they haven’t yet found a conclusive diagnosis. A disease generally refers to a harmful change taking place on a biological level, or a pathological problem of the body’s functioning that produces symptoms. A systemic disease is one that affects the entire body, not just one organ or part.
It’s easy to see how considering depression a systemic disease along the likes of hypertension or diabetes will require a massive shift in traditional perspectives of mental illness and mental disorders. However, the fact that this is not the traditional way of thinking about depression does not mean that it cannot be accurate. Over time, it’s common for perceptions and classifications of health conditions to change as we learn more about them.
Treating Depression as a Systemic Disease
While mind-focused treatments are important for depression, those that target systems of the body may also be key; this, of course, includes pharmacological treatments such as antidepressant medication. Common types of antidepressants are selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs).
Coping With Depression
If you are living with depression, it is important to know how to cope with it both in terms of your mind and body. While talk therapy such as cognitive-behavioral therapy (CBT) targets the mental causes of depression, and medication can target chemical imbalances in the body, there are other approaches you can take as well. Other approaches that can help alleviate symptoms of depression include nutrition, sleep, and exercise—all of which can be useful complements to medical and psychotherapeutic treatments. Try incorporating the following self-care items into your routine:
Eat a nutritious dietGet regular exerciseMaintain a regular sleep scheduleSpend time outdoors (in sunlight)
A Word From Verywell
Many people with depression don’t seek help. They may feel that their depression is a failure on their part. In this way, referring to depression as a systemic disease may help to remove some stigma from this complex disorder. Just because depression can be treated with psychological therapy does not mean the physiological ramifications are any less severe. Seek help for your depression symptoms, just as you would any other illness. Severe cases of depression, in particular, are best treated by a mental health professional who can devise a plan that combines multiple components such as medication, talk therapy, and lifestyle changes.
