Initial Posting: 12/1/2015    Last Update: 1/29/2020
Answer: Turmeric spice is ground (dried) turmeric herb — specifically the root/rhizome, sold as a powder. Consuming between ½ to 1 teaspoon of turmeric powder (about 2.5 to 5 grams) with food has been found to have certain digestive and cognitive benefits.
Most clinical studies, however, have not used turmeric powder, but turmeric extract. Only about 3% of the weight of turmeric powder is curcumin and "curcuminoid" compounds -- which are believed to be important to turmeric's effects. In turmeric extracts, the concentration of these is often increased to as high as 95%.
Therefore, it is not unusual for a capsule containing half of a gram of turmeric extract to provide 400 mg of curcuminoids, while the same amount of turmeric powder (ground herb -- just like the spice) might provide only about 15 mg. In fact, in 2013, ConsumerLab.com found that capsules of turmeric "herb" (not extract) from a well-known supplement brand contained only 3 mg of curcuminoids per capsule. Many brands of turmeric supplements contain a combination of extract and herb, and the ratio will greatly affect the amount of curcuminoids you get, so be sure to check the amounts of curcuminoids in popular supplements in ConsumerLab.com's Review of Turmeric and Curcumin Supplements and Spices >>.
One advantage of using turmeric spice, as opposed to a supplement, is that you are more likely to consume it with fats or oils from your food. This will enhance absorption of curcuminoids in the turmeric, as they are lipophilic (they attach to fats). You should take turmeric supplements with meals for the same reason and/or choose a supplement which includes a bioavailability enhancer (as discussed in detail in the Review). (Be aware, however, that some curcumin may be lost due to heat and chemical changes when cooking foods spiced with turmeric.)
Another way that turmeric extracts differ from turmeric powders is that extracts are less likely to be contaminated with heavy metals, such as lead, and do not contain the filth (insect parts and rodent hairs) normally found to varying degrees in the powders. In the Review, you'll also see our tests of levels of filth and heavy metals in popular turmeric spicesfor cooking, plus the dosage of herb or extract used in treating conditions such as ulcerative colitis, uveitis, arthritis, psoriasis, diabetes, depression, and cognitive function.