This randomized controlled superiority pilot trial will evaluate the efficacy of two vitamin D3 formulations administered over eight weeks in adults with subclinical or clinical vitamin D deficiency. The study will compare changes in serum 25-hydroxyvitamin D concentrations between formulations, as well as the proportion of participants who will achieve vitamin D sufficiency. Both formulations are expected to improve vitamin D status, with the hypothesis that one formulation will demonstrate superior bioavailability, resulting in greater and faster increases in circulating 25-hydroxyvitamin D. The findings will provide preliminary evidence to inform formulation selection and dosing strategies for correcting vitamin D deficiency and will support the design of larger, confirmatory trials.