Vitamin D₃ Bioaccessibility from Supplements and Foods-Gastric pH Effect Using a Static In Vitro Gastrointestinal Model

Vitamin D₃ deficiency is a global phenomenon, which can be managed with supplementation and food fortification. However, vitamin D₃ bioaccessibility may depend on factors such as matrix composition and interactions throughout the gastrointestinal (GI) tract. This research focused on the effect of different matrices on vitamin D₃ content during digestion, as well as the effect of pH on its bioaccessibility. The INFOGEST protocol was employed to simulate digestion. Three different types of commercial supplements, two foods naturally rich in vitamin D₃, and three fortified foods were investigated. High-Performance Liquid Chromatography was used to determine the initial vitamin D₃ content in the supplements and foods, as well as after each digestion stage. The results indicate that the foods exhibited higher bioaccessibility indices compared to the supplements and a higher percentage retention at the end of the gastric phase. The pH study revealed a positive correlation between an increased gastric pH and the corresponding content of vitamin D₃. Interestingly, exposing the matrix to a low pH during the gastric phase resulted in an increased intestinal content of D₃. Vitamin D₃ is more bioaccessible from foods than supplements, and its bioaccessibility is susceptible to changes in gastric pH. Fasting conditions (i.e., gastric pH = 1) enhance the vitamin's bioaccessibility.