Although not all the evidence is in, turmeric is believed to be useful in the treatment of many health conditions because of its anti-inflammatory and antioxidant properties. It's thought it can improve brain function and reduce the risk of brain disease, lower the risk of heart disease, and prevent and treat Alzheimer's Disease. It may also improve the symptoms of arthritis, and be effective in the treatment of depression and age-related chronic disease.
Curcumin, a curcuminoid, is the main active ingredient in turmeric. It's a small molecule that possesses powerful anti-inflammatory qualities and as a result it's being heavily researched for its potential in cancer prevention and treatment.
There is no standard dose for curcumin, but it's thought that to get the benefits you'd need to exceed 1 gram a day, which is difficult to get through food alone. It's one of the reasons why most people take their curcumin as a supplement in conjunction with black pepper (for its piperine) to enhance absorption.