Vitamin c solubility and absorption
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Vitamin C Solubility in Water and Other Solvents
Vitamin C (ascorbic acid) is highly water-soluble, which means it dissolves easily in water and aqueous solutions. Studies show that its solubility in water and water-ethanol mixtures is much higher than in less polar solvents like propan-1-ol or water-propan-1-ol mixtures, making water the most effective medium for dissolving vitamin C for absorption and use in the body . This high solubility is a key reason why vitamin C is classified as a water-soluble vitamin .
Mechanisms of Vitamin C Absorption in the Human Body
Active and Passive Transport
Vitamin C is absorbed in the small intestine, primarily in the proximal part, through both active transport and passive diffusion. The main mechanism involves specific sodium-dependent vitamin C transporters (SVCTs), which actively transport vitamin C across the intestinal mucosa. However, at higher concentrations, passive diffusion can also occur 2589.
Role of Transport Proteins
Specialized transport proteins, especially those in the solute carrier (SLC) family, are crucial for the efficient uptake and cellular distribution of vitamin C. These transporters ensure that vitamin C is absorbed from the gut and delivered to tissues where it is needed 59.
Factors Influencing Vitamin C Absorption
Formulation and Delivery Method
The form in which vitamin C is consumed affects its absorption. Liquid formulations, such as vitamin C drinks, have been shown to result in higher plasma vitamin C levels compared to tablets or capsules. Additionally, individuals with higher muscle mass may absorb vitamin C more efficiently, especially from liquid formulations .
Liposomal vitamin C, which encapsulates the vitamin in lipid layers, significantly increases absorption into both plasma and leukocytes compared to standard vitamin C formulations. This enhanced absorption is likely due to improved stability and transport across cell membranes .
Dose-Dependence and Saturation
Vitamin C absorption is dose-dependent and saturable. At low to moderate doses, absorption is efficient, but as the dose increases, the absorption rate decreases due to saturation of the transporters. Excess vitamin C that is not absorbed is excreted in urine, as the body cannot store large amounts of water-soluble vitamins 78.
pH and Solubility Effects
Vitamin C’s solubility and its ability to enhance the solubility of other compounds, such as iron, are influenced by pH. Vitamin C can increase the solubility of iron at higher pH levels, which in turn improves iron absorption from foods . Additionally, vitamin C can help restore the absorption of certain drugs that are less soluble at higher gastric pH, such as dasatinib, by acidifying the stomach environment and improving drug solubility .
Conclusion
Vitamin C is highly soluble in water, which supports its efficient absorption in the small intestine through both active transport and passive diffusion. The absorption process is influenced by the form of vitamin C consumed, individual physiological factors like muscle mass, and the presence of specific transport proteins. Liposomal and liquid formulations can enhance absorption, while the body’s ability to absorb vitamin C is limited by saturable transport mechanisms. Vitamin C’s solubility also plays a role in improving the absorption of other nutrients and drugs, especially under varying pH conditions. Regular intake is necessary, as excess vitamin C is not stored but excreted from the body.
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