Depression is a highly disabling affliction that targets an estimated 21% of the world’s population (Schechter et al., 2005). It is an exceedingly common disorder and, sadly, the symptoms often go undiagnosed. A great number of studies have been carried out on the causes of depression and chronic stress is often implicated. Reports indicate that chronic stress perpetuate learned helplessness behavior and decreases hippocampal cell proliferation. Although the exact neural substrates underlying the disorder are still under investigation, the hippocampus has received much attention in psychosocial research paradigms.
Curcumin is the active ingredient in Curcuma Longa, more commonly known as the Asian yellow spice, Turmeric. Curcumin’s many therapeutic properties include antioxidant, anti- inflammatory, immunodulatory and neuroprotective activities. Turmeric is well known as an ancient remedy used in Indian Ayurvedic medicine. It is also the major constituent of Xiaoyao-san and Jieyu-wan, the traditional Chinese herbal medicines, which have been used to effectively manage stress and depression-related disorders in China. It is used to treat the symptoms of mental stress, hypochondriac pain and mania.
Curcumin’s antidepressant activity has been attributed to its two primary effects. It is responsible for neurogenesis in the hippocampus and secondly, it raises the level of certain neurotransmitters that have been implicated in causing depression.
Recent studies show that stress-induced damage to hippocampal neurons may be the reason behind depression. Reductions in neurogenesis in the hippocampus and concentrations of brain-derived neurotrophic factor (BDNF) generally result in stress, anxiety and depression. There are, however, a few ways to increase neurogenesis. These include high impact exercise, learning, bright light, and the use of antidepressants. Curcumin also positively affects neurogenesis. The effect of Curcumin on neurogenesis was similar to the impact of exercise and environmental enrichment. Studies involving rats using the chronic unpredictable stress model of depression evinced antidepressant activity of Curcumin. In a 2006 study, the behavioral alterations and elevated serum corticosterone levels in chronically stressed rats were reversed by chronic Curcumin administration as compared to normal mice. Curcumin-induced hippocampal neurogenesis was similar to classic antidepressant Imipramine treatment. The mechanism for Curcumin treatment may involve overcoming the stress-induced behavioral abnormalities and hippocampal neuronal damage by increased cell proliferation and neuronal populations. The birth of new neurons alludes to a capacity for restoration in the adult brain even in the face of aging and neurodegeneration. Curcumin has also been shown to improve cognitive functioning in mouse models. Moreover, Curcumin treatment may even reverse or protect hippocampal neurons from further damage in response to chronic stress, which may underlie the healing power of Curcumin.
The stimulation of neurogenesis represents “another potential useful effect” of Curcumin.
A part of the antidepressant activity of Curcumin can be attributed to the increase in the level of serotonin that is caused by the compound. Neurochemical analysis has revealed that Curcumin dose dependently increased the serotonin levels. This neurotransmitter plays a role in the regulation of mood, sleep, memory, learning, and sexual behavior. It is clear that serotonin plays a role in depression since all of these behaviours are affected to varying degrees in patients with severe depression.
Another way that Curcumin battles depression is by increasing the level of dopamine in the brain. But this effect was observed only when the Curcumin dosage was increased. Dopamine is a neurotransmitter that affects important brain processes that control movement and emotional responses. Recently, dopamine has become the target of many antidepressant drugs. These drugs are further found to be more effective n the presence of Curcumin.
Both these effects of Curcumin, that is, enhancing the availability of serotonin and dopamine in the brain, and neurogenesis are implicated in its antidepressant activity. In addition, people undergoing Curcumin treatment for other ailments, often find a decrease in their depressive episodes which demonstrates the potentiality of Curcumin as an anti-depressant, and shows that it is not just a placebo.
Curcumin has proven useful but it cannot yet be prescribed as a substitute for other antidepressants because the absorption of Curcumin in the human body is quite poor. Scientists are trying to find a way to increase the bioavailability of Curcumin. A potentiation of pharmacological, biochemical, and neurochemical activities was found when Piperine, a black pepper extract and a bioavailability enhancer, was administered along with Curcumin. When given together, Curcumin and Piperine increased the levels of Curcumin in the brain, as opposed to Curcumin by itself.
Although Curcumin may not be very effective by itself, it is found to aid the activity of other antidepressant drugs like Fluoxetine, Venlafaxine, and Bupropion. Antidepressants were found to be more effective when they were administered along with Curcumin. The synergistic effect of this wonder cure, Curcumin, has important reprucussions for the future treatment of depression.