A recent paper has a good review of the studies on curcumin (tumeric) and its effect on insulin. This was an in vivo rat model.
Mohamed Abdel Aziz;et al. The Effect of Curcumin on Insulin Release in Rat-Isolated Pancreatic Islets. Angiology, 61, no. 6 (2010): 557-566
Their theory is based on the observed effect of curcumin, the active ingredient of tumeric, on an enzyme - Heme Oxygenase 1, a mediator of cellular defense against tissue injury. The study that cited above measured the direct effect of curcumin on insulin secreation (increase) and oxidative tissue damage to pancreatic islet cells (decrease).
A paper in Annual Review of Nutrition Reviews states that Curcumin directly interacts with adipocytes, pancreatic cells, hepatic stellate cells, macrophages, and muscle cells. Other structurally homologous nutraceuticals, derived from red chili, cinnamon, cloves, black pepper, and ginger, also exhibit effects against obesity and insulin resistance. Administration of 10 mg curcumin per day for 30 days to eight human subjects increased HDL-cholesterol (good cholesterol), decreased LDL-cholesterol (bad cholesterol).
Targeting Inflammation-Induced Obesity and Metabolic Diseases by Curcumin and Other Nutraceuticals. Bharat B. Aggarwal. Annual Review of Nutrition
Vol. 30: 173-199
Cited within this review:
Srinivasan M. 1972. Effect of curcumin on blood sugar as seen in a diabetic subject. Indian J. Med. Sci. 26:269–70.
Song MJ, Kim KH, Yoon JM, Kim JB. 2006. Activation of Toll-like receptor 4 is associated with insulin resistance in adipocytes. Biochem. Biophys. Res. Commun. 346:739–45
When I looked up tumeric on the Natural Medicines Comprehensive Database it had no information on tumeric being used for diabetes treatment. But, the Natural Medicines Database states that the use of curcumin in treating Uveitis is effective. Uveitis is an inflammation of the middle layer of the eye, common cause of blindness in patients with Multiple Sclerosis. Taking curcumin 375 mg three times daily has been shown to be effective for this condition in a study lasting 12 weeks.
Efficacy of curcumin in the management of chronic anterior uveitis.
Lal B, Kapoor AK, Asthana OP, Agrawal PK, Prasad R, Kumar P, Srimal RC. Phytother Res. 1999 Jun;13(4):318-22.
More research needs to be done with more participants to be sure of how much curcumin is effective in blood glucose, obesity, and other types of inflammation. It is Generally Recognized as Safe (GRAS) in amounts found in foods, and possibly safe in medicinal amounts. If taken as a supplement, it is best absorbed if taken with food.
Does that help you?