The complications of type 2 diabetes (T2D) include cardiovascular disease (CVD) and damage to the kidneys, eyes, and nerves. Oxidative stress, inflammation, and altered blood lipids are characteristics of T2D. Curcumin is a pigment and polyphenol found in turmeric (Curcuma longa, Zingiberaceae) rhizome. It has anti-inflammatory and antioxidant properties. Clinical trials and animal studies indicate curcumin can reduce elevated blood lipids, decrease the production of inflammatory substances, and improve insulin resistance, and that it may have a role in preventing or reducing complications of T2D. The purpose of this randomized, double-blind, placebo-controlled trial was to evaluate the effect of curcumin supplementation on systemic inflammation, serum adiponectin, and lipid profiles in people with T2D.
Patients were recruited from the Health Center of District 2 of Tehran, Iran. Patients were included if they had a diagnosis of T2D based on American Diabetes Association criteria, had T2D for 1-10 years, were 40-70 years of age, had a body mass index (BMI) of 18.5-30.0 kg/m2, and took oral hypoglycemic agents. Patients were excluded if they had liver, kidney, or inflammatory diseases took vitamin or mineral supplements during the past three months or were taking glucocorticoids, nonsteroidal anti-inflammatory drugs, or herbal remedies. Patients were randomly assigned to take three curcumin or matching placebo capsules daily for 10 weeks. Each 500 mg curcumin capsule contained 440 mg curcuminoids (347 mg curcumin, 84 mg demethoxycurcumin, and 9 mg bisdemethoxycurcumin) and 38 mg turmeric oil. The placebo capsules contained rice (Oryza sativa, Poaceae) flour. The curcumin and placebo capsules were provided by Arjuna Natural Ltd. (Kerala, India). Patients were instructed to maintain their usual diet, physical activity, and medications during the trial.
Weight, height, waist circumference, and hip circumference were measured at baseline and at the end of the trial. Fasting blood samples were collected at baseline and at the end of the trial and analyzed for triglycerides (TG), total cholesterol (TC), high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, high-sensitivity C-reactive protein (hs-CRP; a marker of general and cardiac-related inflammation), and adiponectin (an anti-inflammatory substance produced by adipose tissue). Two-day dietary recalls were recorded at the beginning, middle, and end of the trial, and physical activity was evaluated at the beginning and end of the trial. Telephone contacts every 15 days were used to improve compliance, which was monitored by capsule counts at visits. Those who consumed less than 90% of capsules were to be excluded.
A total of 53 patients were enrolled, including 25 in the curcumin group and 28 in the placebo group. A total of 44 patients completed the trial. Four patients in the curcumin group withdrew because of stomach discomfort, noncompliance, or missing the last study visit. Five patients in the placebo group withdrew because of noncompliance, changes in medical treatment, or personal reasons. There were no significant differences in demographic characteristics, dietary intake, polyphenol intake, or physical activity levels between the curcumin and placebo groups at baseline.
TG decreased significantly from baseline to 10 weeks only in the curcumin group (-14.2 ± 30.6 mg/dL, P = 0.03), but the decrease was not significantly greater than that in the placebo group. There were no significant differences in TC, LDL cholesterol, or HDL cholesterol within or between the two groups after 10 weeks. Levels of hs-CRP decreased significantly in the curcumin group (-2.5 ± 4.3 mg/L, P = 0.002), and the decrease was significant compared to the placebo group (P = 0.008). Levels of adiponectin increased significantly in both the curcumin group (12.1 ± 7.7 ng/L, P < 0.0001) and the placebo group (7 ± 7.1 ng/L, P < 0.0001). The increase in the curcumin group was significantly greater compared to the placebo group (P = 0.03).
The authors state that this is one of the few trials of curcumin conducted in people with T2D. In other studies, improvements in lipid profiles have been observed after curcumin supplementation in patients with coronary artery disease and in animal models of diabetic atherosclerosis. The authors attribute the lack of effect on TC, LDL cholesterol, and HDL cholesterol in this trial to the small sample size and short duration. The reduction in hs-CRP in this population confirms findings of reduced hs-CRP and CRP with curcumin supplementation in people with metabolic syndrome and in obese people with diabetes. Elevated CRP levels are independently correlated with increased risk of cardiovascular disease and diabetes. The increase in adiponectin in this population confirms findings from curcumin supplementation in people with prediabetes and metabolic syndrome. Adiponectin levels are inversely related to insulin resistance, dyslipidemia, CVD, and obesity. Curcumin’s anti-inflammatory activity is thought to play a major role in its antidiabetic effects. The authors conclude that curcumin consumption may reduce complications of diabetes by decreasing TG and chronic inflammation.
The authors declare no conflict of interest.
Adibian M, Hodaei H, Nikpayam O, Sohrab G, Hekmatdoost A, Hedayati M. The effects of curcumin supplementation on high-sensitivity C-reactive protein, serum adiponectin, and lipid profile in patients with type 2 diabetes: A randomized, double-blind, placebo-controlled trial. Phytother Res. May 2019;33(5):1374-1383. DOI: 10.1002/ptr.6328.