Abstract

Objectives: Depression is one of the most common psychiatric disorders, and the fourth leading cause of long-term disability throughout the world. Despite the availability of different classes of antidepressant drugs, most of them are not completely effective and above all are associated with many serious adverse effects. Recently, accumulating evidence suggests that dietary supplements rich in important phytochemicals possess beneficial therapeutic roles in depression. Methods: In this review, we will first consider what is known about the pathogenesis of depression and discuss the need for more safe and efficacious treatment. We will then review the potential clinical relevance of natural plant-derived products based on data derived from pre-clinical animal studies, randomized controlled studies and placebo-controlled trials published on this topic within the last decade. Results: Among the natural compounds that show antidepressive-like activity, green tea catechins have been shown to decrease depressive symptoms in experimental animals, possibly in part through the inhibition of monoamine oxidase (MAO). Anthocyanins and their aglycons, responsible for the typical color of berries, inhibit MAO isoforms A or B with IC50 values corresponding to the micromolar range. Other studies suggest that cocoa extracts, whose main components are procyanidins, attenuate depressive symptoms in rats. Resveratrol, one of the most important natural stilbenoid, inhibits noradrenaline and serotonin reuptake in rats, and significantly decreases anxiety/depressive behaviours while increasing hippocampal serotonin and noradrenaline levels. Trans-resveratrol possesses MAO-A inhibitory effects in different brain areas, particularly in the frontal cortex and hippocampus, as already reported for tea catechins. Although these effects have been documented in rodent models, further randomized controlled trials in this area are warranted. However, so far, there is only correlative evidence between certain nutrients, such as omega-3 polyunsaturated fatty acids and B vitamins, and depression in human population studies. Discussion: Growing evidence suggests that consumption of these compounds may represent an alternative strategy to delay the onset and progression of depression, and depressive-like symptoms. However, further randomized and placebo-controlled trials are necessary to confirm the potential of these compounds as a possible remedy for this debilitating disorder.