Turmeric (Cucuma longa) is a member of the ginger (Zingiberaceae) family that is grown commercially in tropical countries for its root (rhizome). The rhizome of the turmeric plant is prized the World over because it has particular medicinal properties in humans and other animals. For medicinal uses the rhizome is dried and powdered where it can be turned into a standardised extract. As well as its medicinal properties, turmeric is also used as a spice in curry powder, mustard and in various foods for its yellow colour. Its antioxidant properties also make turmeric a useful food preserve, one of the reasons it is likely used traditionally in curries. The main active ingredient in turmeric is believed to be a curcumoid called curcumin. However, turmeric also contains a volatile oil comprising of turmerone, bisabolane, curlone, ar-turmerone and zingiberene. This volatile oil gives turmeric its natural aroma. Various sugars, vitamins and minerals are also present in turmeric. Turmeric naturally contains around 0.5 to 5 % curcumin but preparations can be standardised to contain as much as 95 % curcumoids.
Both the volatile oil and the curcuminoids in turmeric are believed to be bioactive and exert significant pharmacological activity in humans. In animals, cell culture and humans studies, turmeric has been shown to possess significant anti-inflammatory, antimicrobial, antioxidant, anticarcinogenic and hepatoprotective effects. The antioxidant effects of turmeric are thought to come primarily from the curcumin content. This is not surprising as curcumin is a phenol (actually a phenylpropanoid) and plant phenols are well researched for their antioxidant capacity. The yellow colour of turmeric means that it can be used in high fat products such as butter margarine and cheese to prevent lipid peroxidation. In humans, curcumin interacts with other antioxidants, sparing cellular levels and boosting overall antioxidant capacity in tissues. This antioxidant effect no doubt confers some protection from cancer. In this regard turmeric has been shown to be beneficial at preventing cancer initiation, propagation and progression.
However, it is the anti-inflammatory effects of turmeric that are most well researched and best understood. The volatile oil fraction of turmeric has been shown to possess significant anti-inflammatory effects in animals, effects which are comparable to currently prescribed anti-inflammatory drugs such as cortisone and other similar drugs. However, the curcumin content is likely the main reason for the anti-inflammatory effects of turmeric. Curcumin has been shown to possess effects against inflammation that are superior to prescribed pharmaceuticals, but in addition shows none of the side effects associated with these compounds. As well as its anti-inflammatory effects curcumin may act in a similar way to capsaicin from cayenne pepper by depleting the nerve ending of substance P. Curcumin is therefore effective at preventing the propagation of pain signals to the central nervous system. In combination with its anti-inflammatory effect this makes curcumin a good treatment for soft tissue injuries.
So how does curcuming inhibit inflammation? Well, the mechanism of action of turmeric on inflammation is not fully understood, but several mechanisms have been suggested and tested clinically in animals and humans. One theory suggests that the curcumoids in turmeric can cause an indirect effect on the adrenal cortex, to modify the release of glucocorticoids (the bodies natural anti-inflammatory compounds). Another theory suggests that the curcumoids in turmeric can decrease the rate of metabolism of glucocorticoids and thus potentiate their action. Alternatively, turmeric may inhibit the 5-lipoxygenase enzyme responsible for the synthesis of pro-inflammatory eicosanoids or inhibit the production of lipopolysaccharide induced cytokines such as tumour necrosis factor alpha (TNF-α) and interleukin-1. Turmeric can also improve liver function and increase bile secretion which may confer beneficial effects against systemic inflammation caused by metabolic dysfunction in the liver.