In this randomized, double-blinded, placebo-controlled clinical trial, we indicated that curcumin supplementation has positive effect in reduction fasting blood glucose, body weight and hip circumference in patients with type 2 diabetes. Although there are some clinical trials that have described the effect of turmeric and its derivatives consumption on glycemic control, oxidative stress and anthropometric indices [3,4,5,6,7,8, 16, 17, 22,23,24,25], but most of these studies have been done on animal models and only a few of them have assessed the impact of curcumin on patients with diabetes and its complications. According to this study daily administration of 1500 mg curcumin could significantly reduce body weight and hip circumference in patients with type 2 diabetes. Also in one study it was showed, Supplementation with 500 mg curcumin for 4 weeks in obese children and adults showed a significant improve in serum adiponectin and lowered leptin levels that both of these factors play an important role in weight control [23]. Also in another clinical trial have been reported that consumption 1200 mg turmeric for a period of 8 weeks could reducing BMI in patients with type 2 diabetes [23]. There are different mechanisms for anti-obesity effects of curcumin, in its most important role declines the expression of genes involved in energy metabolism, lipid accumulation and reduction in intra cells fat [26]. Diet therapy with curcumin in rodent model causes body weight loss and raise lean body mass. In fact, curcumin inhibits the replication of proteins from the pathway of adipogenesis as well as curcumin leads to increase resting metabolic rate (RMR). This component of turmeric have direct effects on lipid metabolism such as reducing TG synthesis and increasing in beta oxidation of free fatty acids with raising metabolism rate and releases some kind of cytokines which are effective in weight loss. On the other hand curcumin inhibits genes expression of inflammatory cytokines like 1, 2, 6, 8, 12 Interleukins and Tumor necrosis factor alpha (TNF-α) by inactivate Nuclear Factor Kappa Beta (NF-ƙB) [27].

This trial demonstrate that daily supplementation with 1500 mg curcumin for 10 weeks could decrease fasting blood glucose in patients with type 2 diabetes, but no significant changes observed in serum insulin level, insulin resistance and HBA1c. According to the study conducted on 2013, receiving 300 mg curcuminoid daily for 3 months could reduce fasting blood glucose, HbA1c and HOMA-IR in participants with type 2 diabetes [28]. However daily supplementation with 2100 mg turmeric for 8 weeks had no significant effect on fasting blood glucose, serum insulin level and HbA1c [3]. There are various mechanisms for anti-diabetic effect of curcumin. One of the most fundamental of these mechanisms is that improvement in beta-cells function through its anti-inflammatory and anti-oxidant properties [7,8,9, 28]. In addition curcumin reduces fasting blood glucose by increasing Peroxisome proliferator-activated receptor (PPAR) activity, inhibits hyperglycemic, increases Glycolysis, inhibits liver gluconeogenesis, stimulations secretion insulin from pancreas, provokes glucose uptake by increasing gene expression of GLUT4, GLUT2 and GLUT3, suppresses liver production through improvement AMP kinase activation and inhibits glucose 6 phosphate kinase [16, 26, 28]. On the other hand curcumin increases the expression of adiponectin genes and thus leads to raising insulin sensitivity [29].

This investigation showed that receive 500 mg curcumin capsule 3 times a day for period of 10 weeks had no significant effect on reducing serum malondialdehyde level and increasing total antioxidant capacity. Oxidative stress reflects an imbalance between production of free radicals and body antioxidant defenses, for example Hyperglycemic could increase production of free radicals and oxidative stress [30]. Actually hyperglycemic through raising mitochondria free radicals production especially Reactive oxygen species (ROS) leads to oxidative stress in diabetes [31]. Curcumin as an antioxidant agent could enhance the expression of antioxidant enzymes and thus increases total antioxidant capacity. Mechanisms that are described for the antioxidant effects of curcumin include, Inhibition of glycosylation of proteins and lipid peroxidation, increased glutathione peroxidase activity, increasing the expression of antioxidant enzymes and enhancing the free radical clearing capacity [8].

In a study that investigated the effect of curcumin on MDA level, curcumin caused significant reduction on MDA level. In other study oral curcumin in diabetic rodent leaded to increase all antioxidant enzymes activity probably due to improve access to glutathione reductase, increased expression of Superoxidase dismutase, catalase and glutathione reductase [15].

The present study had some limitation. First, it seems that 10 weeks administration of curcumin there is not enough time to influence the factors involved in this trial also It was not possible to continue the longer intervention period due to the loss of samples and second, lake of access to nonocurcumin, another form of curcumin that can have significantly therapeutic effect and nanorange formulation. Also there are some reports linking curcumin with iron deficiency anemia. So patients with iron deficiency anemia and using curcumin supplements should be tested for possible causality.