Depression, also known as major depressive disorder (MDD), affects 322 million people worldwide. Approximately 40% of depression is heritable, which leaves room for many influencing factors, such as sex, environment, age, drug use, and socioeconomic status.
Though the cause of depression is not yet clear, inflammation has long been implicated, as it has been correlated with many symptoms of depression. For example, depression is two to three more likely to occur in women, who also suffer from auto-immune and inflammatory disease at higher rates than men. Furthermore, some symptoms of depression are similar to those caused by immune system activation, such as loss of energy, loss of appetite, and fatigue.
Depression is a complex and heterogeneous disease, meaning that it appears differently in each person. However, the two standards for diagnosing depression share nine symptoms, of which five must be met for a diagnosis: depressed mood; markedly diminished interest or pleasure in activities; reduced ability to think or concentrate, or indecisiveness; feelings of worthlessness, or excessive or inappropriate guilt; recurrent thoughts of death, or suicidal ideation, or suicide attempts or plans; insomnia or hypersomnia; significant change in appetite or weight; psychomotor agitation or retardation; and fatigue or loss of energy.
The three main methods of treating depression are 1) antidepressants and other medications that cause antidepressant effects, 2) psychotherapy, and 3) somatic non-pharmacological treatments, which are physical interventions that affect the brain by non-pharmaceutical means. Despite the variety of treatment options, many people are resistant to treatment. In one study, treatment with either an antidepressant or psychotherapy resulted in remission in only 50% of patients.
In the USA, it is accepted that approximately one-third of patients are non-respondent to treatment with traditional antidepressants, a condition known as treatment-resistant-depression (TRD). Thus, research into depression is still ongoing and necessary for the development of future therapeutic interventions.
Source: Roger Li Curieux Academic Journal, issue 50
Inside the Mind 