Recent studies have shown that inflammation may be involved in the pathogenesis of depression. In fact, some research has demonstrated that depression is frequently associated with gastrointestinal inflammations and autoimmune diseases as well as with other ailments in which chronic low-grade inflammation is a significant contributing factor.
It is possible that depression could be a neuropsychiatric manifestation of a chronic inflammatory syndrome. And the primary cause of inflammation may be the dysfunction of the "gut-brain axis".
According to a study reprinted on the website Green Med InfoL
“... [A]n increasing number of clinical studies have shown that treating gastrointestinal inflammations with probiotics, vitamin B, D and omega 3 fatty acids, through attenuating proinflammatory stimuli to brain, may also improve depression symptoms and quality of life. All these findings justify an assumption that treating gastrointestinal inflammations may improve the efficacy of the currently used treatment modalities of depression and related diseases.”