For too long, the public understanding of mental illness has been reduced to a narrow concept: something invisible that happens only in the brain, something manageable with “a positive attitude” or “mental strength.” Mental illness, in this outdated view, is intangible—something to either be ignored or muscled through. But modern science and clinical observation tell a very different story. Mental illness isn’t just a matter of thoughts or mood—it is deeply physiological, systemic, and physical. Depression can cause chronic fatigue and pain. Anxiety can alter digestion, heart rate, and sleep cycles. Trauma can rewire the nervous system. Left untreated, these conditions do more than linger—they break the body down, piece by piece.
Even those working outside of direct clinical care have observed how interconnected mental and physical health really are. Professionals like Thomas Cothren healthcare industry veteran and advocate, have consistently emphasized that addressing mental health in isolation misses the full picture. People struggling with serious conditions like schizophrenia, bipolar disorder, PTSD, or major depression often experience measurable, ongoing physical consequences—especially when their conditions go untreated.
This is not just theory. It’s reality for millions. And understanding this connection is critical if we are to create a healthcare system and social climate that treats mental illness with the seriousness it deserves.
Stress, Cortisol, and the Breakdown of the Body
One of the clearest biological pathways connecting mental illness to physical decline is chronic stress. When a person experiences sustained anxiety, trauma, or depression, the body remains in a heightened state of arousal. This is known as a prolonged activation of the hypothalamic-pituitary-adrenal (HPA) axis, which controls the release of stress hormones like cortisol and adrenaline.
While short bursts of cortisol can help someone cope with immediate danger, chronic elevation wears the body down. Long-term high cortisol levels are associated with hypertension, weight gain (particularly around the abdomen), suppressed immune function, insulin resistance, and increased risk of heart disease. For someone living with an anxiety disorder or PTSD, this stress response may become their baseline—keeping their body locked in a state of physiological alertness that damages them from the inside out.
It’s not uncommon for those with generalized anxiety disorder (GAD) or panic disorder to report heart palpitations, gastrointestinal issues, headaches, and shortness of breath. For many, their first visit to a doctor is prompted by physical symptoms they didn’t initially connect to a mental health condition.
Depression and Physical Functioning
Depression is often perceived as sadness, but its physical footprint is substantial. Major depressive disorder is associated with disturbances in appetite, sleep cycles, energy levels, and even immune system functioning. People with untreated depression are more likely to experience chronic pain, fatigue, digestive issues, and inflammation-related illnesses.
Recent studies have shown that depression is linked with elevated levels of pro-inflammatory cytokines—proteins involved in the body’s immune response. Chronic inflammation has been tied to cardiovascular disease, diabetes, and autoimmune disorders. This may help explain why people with depression are at significantly higher risk of heart attacks and strokes.
Further complicating things, the physical toll of depression often reinforces the emotional burden. For example, someone who is constantly exhausted and experiencing unexplained body pain may become more isolated and less likely to seek care. The overlap of physical and mental symptoms creates a vicious cycle, one that can be hard to break without comprehensive, integrated care.
The Gut-Brain Connection
Another emerging area of study is the relationship between mental health and gut health. The gut is often referred to as the “second brain” due to its complex network of neurons and its critical role in producing neurotransmitters like serotonin and dopamine. In fact, roughly 90% of the body’s serotonin—a neurotransmitter that affects mood, sleep, and digestion—is produced in the gastrointestinal tract.
People experiencing depression or anxiety frequently report digestive problems, including nausea, bloating, constipation, and irritable bowel syndrome (IBS). Recent research suggests this is not coincidental. Stress and mood disorders alter the gut microbiome—the community of bacteria living in the intestines—which in turn can impact mood and cognitive functioning. A disrupted gut-brain axis can make both physical and emotional symptoms worse, creating a feedback loop that’s difficult to escape.
The link is strong enough that some newer treatment approaches to depression and anxiety now include dietary interventions, probiotics, and strategies aimed at supporting gut health alongside traditional therapies.
Trauma and the Nervous System
Trauma leaves a footprint on the body in ways that often go unseen but deeply felt. People who experience acute or prolonged trauma—whether in childhood, war zones, abusive relationships, or other violent situations—often carry the physiological imprint of those events for years, even decades.
The nervous system of someone with untreated trauma doesn’t regulate the same way. Hypervigilance, dissociation, exaggerated startle responses, sleep disruptions, and chronic muscle tension are all common. Over time, these symptoms don’t just affect mental functioning—they contribute to real physical health issues.
Cardiovascular disease, autoimmune disorders, fibromyalgia, and chronic fatigue syndrome have all been linked to unprocessed or untreated trauma. One study found that adults with high Adverse Childhood Experience (ACE) scores—indicators of early trauma—were significantly more likely to develop life-threatening health problems later in life, even when controlling for lifestyle factors like diet and exercise.
Trauma-focused therapies such as EMDR (Eye Movement Desensitization and Reprocessing) and somatic experiencing aim to address the way trauma lives in the body, not just in memory. This is a crucial shift in treatment thinking: emotional wounds do not exist in a vacuum. They alter the biology of the body itself.
Schizophrenia, Bipolar Disorder, and Physical Health Risks
Serious mental illnesses (SMIs) like schizophrenia and bipolar disorder also carry significant physical health burdens. Individuals with these conditions are at higher risk for cardiovascular disease, obesity, diabetes, and respiratory conditions. Some of this risk is due to medication side effects—certain antipsychotics, for example, can increase blood sugar and lipid levels. But much of the risk stems from social and systemic factors, such as poverty, food insecurity, smoking, limited access to preventive care, and stigma within healthcare settings.
People with schizophrenia, on average, die 15 to 20 years earlier than the general population—most often due to preventable physical health conditions. Despite these alarming statistics, their physical symptoms are often dismissed or deprioritized by medical providers, who may attribute physical complaints to psychiatric causes. This is known as diagnostic overshadowing, and it contributes to real harm.
Integrated care models—those that treat mental and physical health in tandem—have been shown to dramatically improve outcomes for people with SMI. Yet these models remain underfunded and underutilized in many healthcare systems.
Rethinking the Entire System
Recognizing that mental illness is physical doesn’t just improve how we think about individuals—it also forces a shift in how systems are structured. Mental health should not be siloed from general health. Emergency departments, primary care offices, and chronic disease management programs must be equipped to recognize and treat the physical manifestations of mental illness. Likewise, therapists and psychiatrists must be trained to recognize when emotional distress may be masking deeper physical illness.
Schools, workplaces, and public health campaigns must also acknowledge the body-mind connection in the way they approach wellness. It’s not enough to offer mindfulness apps or stress seminars. Long-term support, access to full-spectrum care, and education about the physical consequences of untreated mental illness must be central to the conversation.
Ultimately, the false divide between mind and body does more than confuse people—it harms them. When we tell someone it’s “all in their head,” we dismiss the real, biological toll their condition is taking. When we frame mental illness as a matter of willpower or attitude, we deny the overwhelming evidence that mental health is health, period.
A More Honest Understanding of Suffering
People who live with mental illness often carry burdens that go far beyond mood or emotion. Their bodies hurt. Their sleep is broken. Their immune systems are compromised. They age faster. They die younger.
To see them fully, we must be willing to look beyond the brain scan or the diagnosis code. We must understand that suffering is not limited to one part of the self. It travels through every system, every organ, every cell. And so must our care.
The idea that mental illness is “just in your head” is not only wrong—it’s dangerous. The truth is more complicated, and far more important. Because once we understand that mental illness is also in your body, we begin to treat it with the urgency, complexity, and compassion it demands.