For those living with it, depression can be all-consuming. It casts a haze over work, relationships, and everyday social interactions, affecting every aspect of a person’s life. People often think depression solely affects the mind because it's classified as a mental disorder. A new study has shown, however, that depression is more like a systemic disease that affects the entire body.

A team of researchers led by the University of Granada decided to study what happens to the entire body of people who suffer from depression, and focused on stress factors. They conducted a meta-analysis, incorporating 29 previous studies composed of over 3,900 people. The researchers, led by Granada PhD student Sara Jiménez-Fernández, compared patients with depression to healthy controls before and after treatment.

The study, the first work of its kind, found that depression causes an imbalance in the body’s cells called oxidative stress. After receiving the usual treatment for depression, the patients’ levels of malondialdehyde, a biomarker signaling cell deterioration and indicator for oxidative stress, significantly declined from a previously elevated state — so much so that they were indistinguishable from healthy individuals. Zinc and uric acid levels,which drop during times of oxidative stress, also rose until reaching normal levels.

Though this is the first time scientists have shown depression is a systemic disease rather than just a mental one, depression patients have always complained of physical symptoms. Those suffering from depression have commonly reported both insomnia and oversleeping, along with chronic fatigue and decreased appetite for both food and sex.

The results, published in the Journal of Clinical Psychiatry, could explain the significant association between depression and other ailments, including cardiovascular diseases and cancer. It could also shed light on why depression patients tend to have shorter lifespans than non-depressed people.

Source: Jiménez-Fernández S, Gurpegui M, Diaz-Atienza F, Perez Costillas L, Gerstenberg M, Correll C. Oxidative Stress and Antioxidant Parameters in Patients With Major Depressive Disorder Compared to healthy Controls Before and After Antidepressant Treatment: Results From a Meta-Analysis. The Journal of Clinical Psychiatry. 2016.