Non-inferiority RCT on Fish Waste-Derived vs. Synthetic Vitamin D Supplementation in Healthy Adults With Suboptimal Vitamin D Levels

Vitamin D is a fat-soluble vitamin with hormone-like properties, essential for numerous physiological processes in humans. It plays a central role in maintaining calcium and phosphorus homeostasis, promoting intestinal absorption of these minerals, and ensuring optimal bone mineralization. There are two main forms: vitamin D2 (ergocalciferol), primarily obtained from plant sources and supplements, and vitamin D3 (cholecalciferol), synthesized endogenously in the skin through exposure to ultraviolet B (UVB) radiation and present in animal-derived foods such as fatty fish, liver, and egg yolks. Beyond its well-known skeletal functions, vitamin D contributes to muscle contraction, immune system modulation, and regulation of cell proliferation and differentiation. Increasing evidence suggests that adequate vitamin D status may benefit cardiovascular health, glucose metabolism, and possibly reduce the risk of certain cancers, while supplementation has been associated with improved plasma lipid profiles, a relevant factor in cardiovascular risk reduction. The European Food Safety Authority has authorized various health claims for vitamin D, including its role in normal calcium and phosphorus absorption and utilization, maintenance of normal blood calcium concentrations, bone and teeth health, normal muscle function, immune defense, and reduction of the risk of falls in older adults. Despite its importance, vitamin D deficiency is recognized as a widespread public health concern across Europe, with prevalence influenced by latitude, season, skin pigmentation, and lifestyle habits. Data indicate that up to 40% of Europeans have suboptimal vitamin D levels, with deficiency rates exceeding 70% in specific high-risk groups such as elderly individuals, people with dark skin, and those with limited sun exposure. In Italy, despite abundant sunlight, vitamin D insufficiency is highly prevalent, particularly in older adults and patients with chronic illnesses. Contributing factors