These two are randomised, double-blind, placebo-controlled trials in overweight participants aged 50 to 69 years.
In both studies, the participants took a test food with a hot water extract of C. longa or without the extract daily for 12 weeks.
Their fasting serum glucose and serum high-sensitivity C-reactive protein (hsCRP) levels were then measured.
The changes in hsCRP level were measured as hsCRP is a marker of inflammation.
In this analysis, the researchers categorised the trial participants into two groups based on their baseline level of hsCRP – namely low hsCRP (mean hsCRP less than 0.098 mg/dL) versus high hsCRP (mean hsCRP equivalent or higher than 0.098 mg/dL).
“In the low-hsCRP subgroup, we found no significant difference in fasting serum glucose levels between the two groups [intervention versus placebo] in either study.
“But in the high-hsCRP subgroup, the C. longa extract group had significantly lower levels of serum hsCRP (p < 0.05) and fasting serum glucose (p < 0.05) [in the intervention group] than the placebo group in both studies,” said the researchers.
For example, in the 2019 study, blood glucose level in subjects with low hsCRP taking the C. longa extract had increased by 0.8 mg/dL from the baseline by the end of the trial.
However, in subjects with high hsCRP taking the C. longa extract, their blood glucose level had significantly decreased by 2.0 mg/dL by the end of the trial.
Similarly, in the 2021 study, blood glucose level in subjects with low hsCRP taking the C. longa extract had increased by 0.008 mg/dL from the baseline by the end of the trial.
In subjects with high hsCRP taking the C. longa extract, their blood glucose level had significantly decreased by 3.6 mg/dL by the end of the trial.
“Therefore, these results suggest that C. longa extract may improve systemic glucose metabolism associated with chronic low-grade inflammation and could possibly decrease the risk of prediabetes and type 2 diabetes,” the researchers added.
They hypothesised that the C. longa extract worked by suppressing the activation of the NF-kB signaling pathway and the production of inflammatory cytokines.
The trials were conducted by a Japanese contract research organisation known as CPCC Co. Ltd, with financial support from House Wellness Foods Corp.
A Hot Water Extract of Curcuma longa L. Improves Fasting Serum Glucose Levels in Participants with Low-Grade Inflammation: Reanalysis of Data from Two Randomized, Double-Blind, Placebo-Controlled Trials
Authors: Ryusei Uchio et al