Vitamin C: Does Liposomal Formulation Make a Difference?

Vitamin C (ascorbic acid) is an essential nutrient for physiologic and metabolic function in humans. Adequate intake of vitamin C is necessary to maintain health, prevent deficiency, and decrease the risk for disease such as scurvy. ¹ Notably, vitamin C also plays a major role in supporting immunity and infection resistance.¹ As an antioxidant, vitamin C enhances chemotaxis, improves phagocytosis, aids microbial killing, and regulates apoptosis.^1,2 Other functions include serving as a cofactor in collagen biosynthesis, carnitine, and catecholamine metabolism; regeneration of other antioxidants; improved absorption of iron, calcium, and folic acid; improved wound healing; and repair and maintenance of cartilage, bone, and teeth.¹

Foods high in vitamin C include citrus fruits, berries, tomatoes, potatoes, bell peppers, and cruciferous leafy vegetables. Variability in the amount of vitamin C obtained from diet exists due to the instability of vitamin C during cooking, storage, and food processing.² Therefore, eating different sources of vitamin C is encouraged. Dietary intake is key, but vitamin C can also be obtained via supplementation. Vitamin C supplements generally contain ascorbic acid and are available in various forms marketed as either individual components or coformulations.³

Vitamin C pharmacokinetics are complex, tightly regulated, and influenced by dose, concentration, tissue-specific factors, dose-dependent absorption, tissue-specific distribution, minimal hepatic metabolism, and regulated excretion. Vitamin C reaches its maximum plasma concentration approximately 2 to 3 hours after ingestion.² Vitamin C bioavailability has been reported as 70% to 90% when supplemented and 73% to 80% when obtained from fruits and vegetables.² Absorption is efficient at low to moderate oral doses (30-180 mg/day), with up to 90% bioavailability.² Doses greater than 1000 mg/day result in less than 50% absorption. At these higher doses, absorption is limited due to specific transporter saturation.^2,3This transporter saturation results in a shift from first order to zero-order kinetics in which further increases in dose no longer proportionally raise systemic availability of vitamin C. With a half-life of approximately 2 hours in plasma, multiple daily doses of vitamin C are required to sustain optimal systemic concentrations.² Vitamin C is water-soluble, given its hydrophilic nature, and results in minimal storage in the body. Excess vitamin C is excreted in urine, requiring frequent and routine intake to combat deficiency.³

The recommended dietary allowance is 90 mg/day for men and 75 mg/day for women, with a tolerable upper intake limit of 2000 mg/day.⁴ This daily allowance is higher than allowances to prevent deficiency and has been shown to aid immunologic and antioxidant functions. However, the recommendation does not account for elevated demand during physical or psychological stress. The challenge is striking a balance between maintaining adequate vitamin C stores to support biological function and avoiding doses that exceed absorptive capacity and are subsequently excreted.

Vitamin C Impact on Immunity

Researchers have evaluated the effect vitamin C supplementation has on common cold symptoms, including total duration and severity.⁵ All placebo-controlled trials of orally administered vitamin C, in doses of at least 1000 mg/day for the common cold among individuals in good health at baseline, were included. Participants ranged from children to adults, including military and athlete subgroups. Vitamin C reduced the more severe measures of the common cold by 26%. However, there was no evidence of effect on mild cold symptoms. Vitamin C shortened the duration of absence from school and days confined to house by 15%. In some instances, days confined to house were reduced by 0.26 to 1.12 days.⁵

Different effects on durations of mild and severe cold symptoms were identified. The reduction effects of 15% and 26% are approximations for the magnitude of the effect of vitamin C on severe common cold symptoms. These reductions should not be considered as universal estimates. Vitamin C supplementation did not significantly reduce the incidence of colds in the general population but did reduce risk in those experiencing physical stress (ie, athletes, individuals in contact with young children, military personnel). Participants experienced reduced nasal congestion, less sore throat, and lower symptom burden.⁵ In a previous Cochrane review on vitamin C and the common cold, the same researchers identified that regular vitamin C supplementation of just 200 mg/day or more also shortened the duration of colds by 9.4% (p<0.00001).⁶

Liposomal Delivery

Vitamin C is easily degraded in water, at high pH, and in the presence of oxygen and metal ions.¹ A major challenge is maintaining vitamin C stability in food products or dietary supplements.⁷ Oral conventional forms of vitamin C are typically administered in the crystalline form or as a solution, resulting in a high rate of degradation in the gut.⁷ Ensuring vitamin C is well absorbed is paramount because it directly impacts bioavailability. Shielding against degradation while prolonging absorption, leading to enhanced bioavailability, is necessary and may be achieved through different oral delivery modes, including encapsulation.⁸

Encapsulation involves a bioactive compound (core material) being covered by a continuous synthetic or natural polymer (wall material). Different versions of wall material exist, with the goal of protecting vitamins against adverse conditions such as light, oxygen, heat, and humidity.⁸ Liposomes are vesicles with a membrane composed of phospholipids and cholesterol, and are considered biocompatible due to their structural similarity to cell membranes.¹ Liposomes can be taken up intact, releasing vitamin C once inside target cells (eg, leukocytes).⁷ Other routes of absorption include endocytosis and lymphatic pathways, thereby reducing reliance on saturable vitamin C transporters. Liposomes are an attractive delivery system because they exhibit low toxicity, provide targeted transport and controlled release, and are cost-effective and easy to prepare.^1,8

Liposomes have demonstrated efficacy at preventing degradation of vitamin C in the gut. Liposomal vitamin C has been formulated to improve delivery increasing absorption and bioavailability, in turn improving efficacy and tolerance of vitamin C compared to conventional vitamin C formulations which have tolerance challenges (eg, upset stomach, heartburn, nausea, diarrhea). Lipid aggregates and metabolites have been used to protect vitamin C in the gut, allowing larger doses of vitamin C to be administered. Liposomal delivery has resulted in vitamin C reaching the maximum blood concentration by approximately 1 hour and has shown elevation of blood plasma concentration from 180 μM to 303 μM compared to conventional vitamin C.

Liposomal Vitamin C Studies

Gopi and Balakrishnan conducted an oral bioavailability study with 24 participants.⁹ The study compared 1000 mg liposomal vitamin C to non-liposomal vitamin C (ascorbic acid). A key finding was oral liposomal vitamin C was approximately 1.8 times more bioavailable, with higher values for Cmax and AUC compared to non-liposomal vitamin C. With a higher peak plasma concentration and exposure over time, liposomal vitamin C demonstrated longer retention and sustained release compared to non-liposomal vitamin C.⁹

Wen et al. performed a crossover trial with 11 participants. The intervention included vitamin C without liposome, followed by 14-day washout period, then liposomal process A (vitamin C with lecithin), and, after another 14-day washout, liposomal process B (vitamin C with lecithin and high-pressure homogenization).¹⁰ Vitamin C levels in plasma weremeasured at baseline and 0.5, 1, 2, 3, 4, and 8 hours post-supplementation. Liposomal process B enhanced absorption, extended plasma retention, and improved bioavailability compared to liposomal process A and placebo, suggesting improved systemic delivery and duration of action compared to conventional vitamin C.¹⁰

Purpura et al. investigated whether a liposomal form of vitamin C could enhance absorption compared to placebo and ascorbic acid.¹¹ Twenty-seven participants received a 500 mg dose of each formulation (liposomal vitamin C, ascorbic acid, or placebo).Plasma and leukocyte vitamin C concentrations were measured at 0, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, and 24 hours after ingestion of a single 500 mg dose of each form. Standard ascorbic acid and liposomal vitamin C significantly increased vitamin C levels compared to placebo (p < 0.001) and liposomal vitamin C resulted in higher concentrations in both plasma and leukocytes, indicating improved absorption (Cmax [plasma +27%, leukocytes +20%, p < 0.001] and AUC0-24 h [plasma +21%, leukocytes +8%, p < 0.001]) compared to standard ascorbic acid. Liposomal encapsulation enhanced the bioavailability of oral vitamin C compared with the same dose of conventional vitamin C.² The increase in both plasma and leukocyte vitamin C suggests liposomal delivery improves absorption and cellular uptake beyond what is seen with conventional vitamin C supplements, indicating potential for better systemic and immune-related vitamin C status from liposomal vitamin C at typical supplemental doses.¹¹

Conclusions

Achieving and sustaining optimal plasma levels of vitamin C remains challenging due to its dose-dependent absorption, tissue saturation, short half-life, and rapid renal clearance. Liposomal vitamin C may offer 3 theoretical advantages over conventional formulations: minimizing vitamin C transporter saturation, protecting vitamin C from degradation during digestion, and enhancing uptake into leukocytes. However, the available evidence is limited by small study populations, variability in liposomal formulations and dosing regimens, and study designs that primarily evaluate pharmacokinetic outcomes rather than immune function. Although liposomal formulations may increase circulating vitamin C levels and leukocyte uptake, it remains unclear whether these differences translate into clinically meaningful improvements in immune performance. Although leukocyte vitamin C concentrations are often considered a more functional tissue-level marker than plasma levels, there is insufficient evidence to determine whether higher leukocyte concentrations improve immune responses when cells are activated.

Liposomal encapsulation enhances the bioavailability of oral vitamin C.^9-11 The increase in both plasma and leukocyte vitamin C suggests the liposomal form improves absorption and cellular uptake beyond what is seen with conventional vitamin C supplements.¹¹ Vitamin C is not a treatment or strong preventative measure because regular supplementation does not consistently prevent cold incidence, though it may slightly reduce duration and severity in some groups and is most effective in individuals under stress or experiencing heavy physical exertion.^3,4

With the absolute benefit of liposomal vitamin C yet to be determined, it is reasonable for the general population to trial a conventional vitamin C formulation. Dosing may be optimized by targeting 200 mg to 500 mg per dose multiple times per day with a total daily dose of 1000 mg. Benefits of smaller, more frequent dosing of conventional vitamin C include mitigating transporter saturation, decreasing loss due to degradation, and reducing excretion in urine seen with larger single doses (ie, >1000 mg per dose). Alternatively, if increased dosing frequency is a barrier and intolerance of oral conventional vitamin C forms exists, oral liposomal vitamin C offers potential advantages, including improved tolerance, delivery, and bioavailability. Given the safety profile, modest boost in immunity, and recognized health benefits of vitamin C, regular supplementation may be justified in some contexts. More robust research is required to determine its conclusive impact on immune function.

About the Authors

Corey Paz, PharmD, MBA, BCPS, is in the Executive Sports Pharmacy Certificate Program at the University of Southern California Mann School of Pharmacy & Pharmaceutical Sciences.

Kari L. Franson, PharmD, PhD, is a professor in the University of Southern California Mann School of Pharmacy & Pharmaceutical Sciences.

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