Journal of Complementary and Alternative Medical Research

Preparations of the calyces of Hibiscus sabdariffa L. are consumed widely as beverages and are marketed increasingly as supplements for cardiometabolic risk reduction. Interest in their glycaemic actions has grown because the plant is inexpensive, culturally familiar across tropical and subtropical regions, and rich in anthocyanins and phenolic acids with demonstrable activity against carbohydrate-digesting enzymes. Enthusiasm in the secondary literature has outpaced the primary evidence. Pooled analyses report small reductions in fasting plasma glucose, yet the trials contributing to those estimates were designed principally to test blood pressure or lipid endpoints, rarely enrolled populations defined by glycaemic criteria, and seldom measured glycated haemoglobin or validated indices of insulin sensitivity. This critical narrative review evaluates the strength, coherence and translational relevance of evidence on H. sabdariffa supplementation and glycaemic control in adults with type 2 diabetes mellitus or the metabolic syndrome. Literature was identified through structured searching of scholarly databases and citation tracking, appraised against design-specific criteria, and synthesised thematically around botanical and compositional heterogeneity, mechanistic plausibility, trial-level internal validity, quantitative pooling, and safety. The mechanistic case for an acute postprandial effect through inhibition of alpha-glucosidase and alpha-amylase is reasonably well supported, whereas the case for sustained improvement in chronic glycaemic control rests largely on small, short, heterogeneous trials with inconsistent findings and on rodent models that use exposures far exceeding realistic human intake. The most rigorously conducted syntheses reach markedly more cautious conclusions than less stringently appraised ones, and the largest recent placebo-controlled trial in metabolic syndrome found no effect on insulin resistance or glycaemic markers. Product characterisation is rarely adequate to permit replication or dose inference. Priorities for future work include adequately powered trials in glycaemically defined populations, with glycated haemoglobin or continuous glucose monitoring as primary outcomes, chemically standardised interventions, and pre-registered analysis plans. On present evidence, H. sabdariffa cannot be recommended as a glucose-lowering intervention, although its potential as an adjunct within multifactorial risk management remains open.