Hibiscus sabdariffa inhibits α-glucosidase activity in vitro and lowers postprandial blood glucose response in humans

Hibiscus sabdariffa (HS) is a rich source of anthocyanins, associated with lowering of blood pressure and modulation of blood lipids. There is limited evidence on the effects of HS on postprandial glycaemia and/or chronic markers of glycaemic control. The current study aimed to establish in vitro and in vivo anti-diabetic properties of HS, and to investigate the contribution of individual anthocyanins to inhibit the carbohydrate digesting enzymes α-amylase and α-glucosidase.

A randomized controlled cross-over study was conducted to establish HS effects on postprandial glucose response. Fifteen healthy participants consumed either a low or high dose of HS drink or a sugar matched control drink, alongside a portion of white bread to provide in total 50 g available carbohydrates. Blood glucose was monitored at regular intervals over 3 h with subsequent analysis of plasma insulin. Enzyme activities were determined using absorbance based methods.

The results demonstrate significant attenuation of postprandial glucose (low and high dose) and insulin responses (high dose only) following HS consumption in vivo which was supported by in vitro dose-dependent inhibition of α-glucosidase (IC50 120.9 μg polyphenols/mL), but not α-amylase activity. Moreover, when applied with acarbose, HS showed an increased inhibition of α-glucosidase. The α-glucosidase inhibitory response is likely a combined result of the different components of HS as anthocyanins individually were unable to demonstrate inhibition at concentrations below 100 μM. In conclusion, consumption of HS demonstrates potential to beneficially impact mechanisms contributing to blood glucose regulation, and regular consumption should therefore be encouraged.