Depression is usually seen as a mood disorder related to the brain. But in reality, it is a disorder that affects the entire body. One of the most characteristic symptoms is fatigue, which robs a person of the strength to act. However, the changes are not limited to the psyche: depression disrupts metabolism, lowers physical and mental energy levels, and affects almost all bodily systems. It alters sleep and appetite, intensifies the perception of pain, weakens the immune system, and forms a gloomy worldview in which a person sees no future. Most cases of depression manifest primarily through physical symptoms: chronic pain, fatigue, and digestive issues.

Why does depression exhaust you?

For most people with this disorder, fatigue is one of the first and last symptoms. It makes a person irritable and apathetic, stripping away concentration and interest in life. Sleep is not restorative and only deepens the feeling of exhaustion.

Scientists believe the cause lies in systemic inflammation. Depression symptoms resemble “sickness behavior” in animals: decreased activity, withdrawal from social contacts, and indifference to food or pleasant stimuli. All of this is triggered by cytokines—signaling molecules of the immune system that cause inflammatory processes.

Does depression damage the brain?

The longer a depressive episode lasts, the higher the likelihood of recurrence. This is because depression physically changes the brain. Prolonged stress and the continuous release of hormones lead to a shrinkage of the hippocampus—the area responsible for memory. This is why many patients complain of forgetfulness.

Untreated depression also changes the function of mitochondria—the “power plants of cells”—which is especially important for the brain. This increases the risk of dementia, which is why depression is increasingly being described as similar to neurodegenerative diseases.

How is depression related to pain?

Chronic pain and depression mutually reinforce each other. Research shows that depression activates brain centers responsible for pain, specifically the cortex and subcortical structures. The higher this activity appears on scans, the more severe the symptoms. Interestingly, antidepressants help not only to improve mood but also to reduce the intensity of physical pain.

The immune system and depression

Immunity plays a key role in the development of depression. Inflammatory molecules (cytokines) released during stress or illness can cross the blood-brain barrier and alter brain function. This results in apathy, fatigue, and a loss of interest in social contact and pleasure.

How does depression affect weight?

Metabolic disruption is another feature of this disorder:

• Stress hormones increase insulin resistance and promote fat accumulation in the abdominal area;
• A lack of motivation leads to a sedentary lifestyle and, consequently, weight gain;
• Conversely, some patients experience sudden weight loss due to a loss of appetite.

In this way, depression increases the risk of diabetes and cardiovascular diseases.

The heart and depression

Feeling depressed after a heart attack is common, but depression itself is an independent risk factor for heart disease. It increases the levels of inflammatory substances and affects blood clotting and the autonomic nervous system. All of this raises the risk of arrhythmias and heart attacks.

A study involving 150,000 people in 21 countries showed that in those with at least four symptoms of depression, the risk of cardiovascular events and mortality increased by 20%. This risk was found to be twice as high in men as in women.