Comprehensive Stability Study of Vitamin D3 in Aqueous Solutions and Liquid Commercial Products

Abstract

Vitamin D3 has numerous beneficial effects, such as musculoskeletal, immunomodulatory, and neuroprotective. However, its instability is the main obstacle to formulating quality products. Despite increased attention and growing use, data on vitamin D3 stability is scarce because data from individual studies is inconclusive and mostly qualitative. Therefore, we have systematically investigated the influence of various factors (temperature, light, oxygen, pH, concentration, and metal ions) on its stability in aqueous media using a stability-indicating HPLC-UV method. First-order kinetics fitted its degradation under all tested conditions except light and oxygen. In both cases, the established models in chemical kinetics were inappropriate and upgraded with the Weibull model. Metal ions and acidic conditions had the main destabilizing effect on vitamin D3 in aqueous media, but these solutions were successfully stabilized after the addition of ethylenediaminetetraacetic acid (EDTA), ascorbic acid, and citric acid, individually and in combination. EDTA showed the most significant stabilizing effect. Synergism among antioxidants was not observed. Our findings on vitamin D3 instability in aqueous media also correlated with its instability in commercial products. Vitamin D3 aqueous products require proper stabilization, thereby signifying the importance and contribution of the obtained results to the formulation of stable and quality products.

Keywords: HPLC-UV; antioxidants; cholecalciferol; degradation kinetics; food supplements; medicines; stability; stabilization.

Figure 1

Effect of the media on vitamin D3 stability at 25 °C (n = 3).

Figure 2

pH profile of vitamin D3 in aqueous solutions at 25 °C (n = 3).

Figure 3

Stability of vitamin D3 in distilled water solutions exposed to light (DW–UV) and protected from light (DW–UV protected) at 25 °C (n = 5).

Figure 4

Effect of oxygen on vitamin D3 stability at 15 °C (n = 5).

Figure 5

First-order rate constants for vitamin D3 degradation as a function of different concentrations of ascorbic, citric acid, or EDTA at 25 °C (n = 3).

Figure 6

Vitamin D3 stabilization, presented by its first-order rate constants at 25 °C in distilled water (DW) and after the addition of an individual antioxidant EDTA (E), citric acid (C), ascorbic acid (A), and combinations of two and all three antioxidants (CA, CE, EA, and CAE) (n = 3). The columns designated by different letters showed statistical differences from the other groups (p < 0.001). Insert—The effect of the same concentration (0.5 g/L) of citric acid (C), ascorbic acid (A), or EDTA (E) on vitamin D3 degradation rate at 25 °C (n = 3). The columns designated by different group letters showed statistical differences from other groups (p < 0.001).