A summary of the study “Curcumin and/or omega-3 polyunsaturated fatty acids supplementation reduces insulin resistance and blood lipids in individuals with high risk of type 2 diabetes: a randomised controlled trial”
Background
The study by Thota et al (2019), published in Lipids in Health and Disease in January 2019, aimed to evaluate the effects of supplementing with curcumin and/or long-chain omega-3 polyunsaturated fatty acids (LCn-3PUFA) on glycaemic control and blood lipid levels in individuals at high risk of developing type 2 diabetes (T2D). Lowering insulin resistance (IR) and dyslipidaemia are seen as attractive strategies to reduce the risk of T2D by potentially enhancing glycaemic control and preserving β-cell function. IR is a marked independent predictor of progression to T2D in high-risk individuals. IR is often associated with increased circulating triglycerides (TG), a common feature in individuals with IR and metabolic syndrome.
Methodology
This was a 12-week, 2 × 2 factorial, randomised, double-blinded, placebo-controlled study. Participants were individuals aged 30 to 70 years with a BMI between 25 and 45 kg/m², diagnosed with impaired fasting glucose (IFG) or impaired glucose tolerance (IGT), or having an AUSDRISK score of 12 or more. A total of sixty-four participants completed the study. The participants were allocated to one of four groups: double placebo (PL), curcumin plus placebo (CC), LCn-3PUFA plus placebo (FO), or curcumin plus LCn-3PUFA (CC-FO). The curcumin group received 180 mg of curcumin per day, and the LCn-3PUFA group received 1.2 g DHA + EPA per day.
The primary outcomes evaluated were glycaemic indices, including HbA1c, fasting glucose, and insulin. Insulin resistance and sensitivity were measured using the homeostatic model assessment (HOMA) model. Secondary outcomes included lipid profile (total cholesterol, triglycerides, HDL-C, LDL-C), C-reactive protein (CRP), and whole blood cell count. Compliance to the interventions was high, averaging 94.86 ± 5.8%.
Results
Regarding glycaemic indices, HbA1c and fasting glucose remained unchanged across all groups after 12 weeks. However, fasting insulin was significantly reduced only in the CC group compared to baseline and the placebo group. Similarly, insulin sensitivity (HOMA-S) was significantly improved in the CC group compared to placebo (32.7 ± 10.3% vs PL P = 0.009). FO and CC-FO groups tended to improve insulin sensitivity, but this did not reach significance. Subgroup analysis suggested LCn-3PUFA supplementation might be more beneficial for fasting plasma glucose in participants with higher baseline glucose levels (> 5.5 mmol/L).
For blood lipids, triglyceride levels significantly increased in the PL group, but CC, FO, and CC-FO supplementation all significantly reduced triglycerides when compared to PL. The FO group showed the greatest reduction in triglycerides (−16.4 ± 4.5%, P < 0.001). The Atherogenic Index of Plasma (AIP) was also significantly reduced in the FO, CC, and CC-FO groups compared to PL. No significant differences were observed between groups for total cholesterol, HDL-C, LDL-C, or Total:HDL-C ratio. Both CC and FO significantly reduced InsuTAG levels compared to placebo. Neither curcumin nor LCn-3PUFA, alone or in combination, significantly affected CRP levels. WBC counts were reduced from baseline in the CC and FO groups, but this was not significant in the between-group analysis compared to placebo.
Conclusions
The authors concluded that curcumin supplementation is effective in lowering serum insulin levels and improving insulin sensitivity. LCn-3PUFA supplementation profoundly reduced dyslipidaemia (specifically triglycerides and AIP). While both interventions show potential for lowering key risk factors for T2D, the study failed to demonstrate complimentary benefits of curcumin and LCn-3PUFA on glycaemic control or additive effects when combined. This lack of combined benefit might be due to uncertainties of co-administration, heterogeneity of the study population, gender balance, or unknown interactions. Subgroup analysis suggested gender and baseline glucose status might influence outcomes. Further research, potentially with a single formulation and longer duration, is warranted.
References
Thota, R. N., Acharya, S. H., & Garg, M. L. (2019). Curcumin and/or omega-3 polyunsaturated fatty acids supplementation reduces insulin resistance and blood lipids in individuals with high risk of type 2 diabetes: A randomised controlled trial. Lipids in Health and Disease, 18(1), 31. https://doi.org/10.1186/s12944-019-0967-x
