Advances in Vitamin D encapsulation: from lipid formulations to polymeric nanoparticles

Vitamin D deficiency has emerged as a global public health concern, with implications spanning skeletal disorders, cardiovascular diseases, immune dysfunction, and cancer. Despite its biological importance, effective delivery of Vitamin D remains challenging due to its highly lipophilic nature, poor aqueous solubility, and susceptibility to degradation. These physicochemical limitations necessitate the development of advanced delivery systems capable of enhancing stability, bioavailability, and controlled release. In this review, we examine the current understanding of Vitamin D delivery with particular attention being given to colloidal systems such as emulsions, nanoemulsions, liposomes, and micelles, as well as polymeric nanoparticles and hybrid assemblies, which have shown significant promise for encapsulating lipophilic bioactives and improving their bioaccessibility. We discuss how key parameters, including interfacial composition, particle size, and structural organisation, govern the encapsulation efficiency and release behaviour of Vitamin D. Furthermore, we compare the delivery characteristics of the two principal forms, ergocalciferol (Vitamin D2) and cholecalciferol (Vitamin D3), within these systems, highlighting differences in stability and biological performance. Emerging approaches leveraging self-assembly, responsive polymers, and multifunctional carriers are also critically evaluated. Overall, this review provides a formulation perspective on Vitamin D delivery, identifying current challenges and outlining future directions for the rational design of next-generation delivery platforms.