The active constituent is known as curcumin. It has been shown to have a wide range of therapeutic actions. First, it protects against free radical damage because it is a strong antioxidant. Second, it reduces inflammation by lowering histamine levels and possibly by increasing production of natural cortisone by the adrenal glands. Third, it protects the liver from a number of toxic compounds. Fourth, it has been shown to reduce platelets from clumping together, which in turn improves circulation and may help protect against atherosclerosis. There are also test-tube and animal studies showing a cancer-preventing action of curcumin. In one of these studies, curcumin effectively inhibited metastasis (uncontrolled spread) of melanoma (skin cancer) cells. This may be due to its antioxidant activity in the body. Curcumin inhibits HIV in test tubes, though human trials are needed to determine if it has any usefulness for treating humans with this condition.
A preliminary trial in people with rheumatoid arthritis found curcumin to be somewhat useful for reducing inflammation and symptoms such as pain and stiffness. A separate double-blind trial found that curcumin was superior to placebo or phenylbutazone (an NSAID) for alleviating post-surgical inflammation.
While a double-blind trial has found turmeric helpful for people with indigestion, results in people with stomach or intestinal ulcers have not shown it to be superior to a placebo and have demonstrated it to be less effective than antacids.
Preliminary research indicates a possible benefit of oral curcumin supplementation (375 mg of turmeric extract with 95% curcuminoids three times daily for 12 weeks) for chronic anterior uveitis (inflammation of the iris and middle coat of the eyeball).