Encapsulation Strategies for Improving Micronutrient Bioavailability: Mechanisms, Evidence, and Limitations Across Food Systems

Micronutrient deficiencies remain a major global public health challenge despite decades of fortification and supplementation. Encapsulation has been widely proposed to improve the stability and delivery of vitamins, minerals, carotenoids, and other bioactive compounds, yet whether gains in physicochemical stability and in vitro bioaccessibility translate into improved bioavailability remains uncertain. This review critically evaluates the evidence linking encapsulation performance to biological outcomes across in vitro digestion, cellular, animal, and human studies, considering food matrix interactions, gastrointestinal conditions, release kinetics, transporter-mediated uptake, and first-pass metabolism. Across 60 qualitatively graded studies, encapsulation showed positive effects in 55%, mixed or inconclusive outcomes in 42%, and negative effects in 3%, with positive findings concentrated in in vitro and animal models. Human trials represented only 17% of the evidence, and reproducible benefits were largely limited to liposomal vitamin C. Favorable outcomes predominated in simpler models and pharmacokinetic endpoints, whereas neutral or negative findings increased with physiological complexity and functional endpoints. Encapsulation can address specific stability-related limitations but remains constrained by biological factors, scalability, cost, and regulatory barriers. It should therefore be regarded as a context-dependent rather than universal strategy for improving micronutrient bioavailability.