Do Liposomal Vitamin C Formulations Have Improved Bioavailability? A Scoping Review Identifying Future Research Directions.

Due to the essential requirement of vitamin C (ascorbate) by humans, formulation of the vitamin to increase its bioavailability is of relevance, particularly for those with higher requirements for the vitamin. In this scoping review, studies assessing the bioavailability of liposomal versus non-liposomal ascorbate were identified through database and manual searching and relevant pharmacokinetic data were extracted. Of the 321 studies identified, 10 were included in the final review. Seven of the trials used randomised crossover designs, one used parallel groups and two were non-randomised. Vastly different liposomal formulations, ascorbate doses (0.15-10 g) and sample collection durations (4-24 h) were used, thereby making it difficult to directly compare the studies. Nevertheless, nine of the studies showed higher bioavailability of liposomal versus non-liposomal ascorbate: 1.2-5.4-fold higher Cmax and 1.3-7.2-fold higher AUC. However, none of the studies assessed ascorbate elimination; therefore, it is uncertain whether the ratios of liposomal to non-liposomal ascorbate in urine are equivalent to those observed in plasma. Furthermore, only two of the studies assessed in vivo cellular uptake and only two assessed potential biological effects. Thus, future studies should include urinary elimination and cellular uptake kinetics, assess participants with low baseline status and investigate potential biological effects. SUMMARY: Due to the essential requirement of vitamin C by humans, formulations to increase its uptake into the body are of relevance, particularly in those with higher requirements for the vitamin. In this review, studies assessing the uptake of liposomal versus non-liposomal vitamin C were investigated; liposomal vitamin C comprising the vitamin encapsulated within lipids. Ten studies were identified, which administered different liposomal formulations, vitamin C doses (0.15-10 g) and sample collection durations (4-24 h). Nine of the studies showed higher uptake of liposomal vitamin C. Future studies should assess urinary excretion, cellular uptake and biological effects of liposomal vitamin C.