Vitamin C: Sources, Benefits and Supplements

Vitamin C (also known as ascorbic acid), plays an important role in several physiological functions. Humans can’t synthesise vitamin C due to the lack of an enzyme named gulonolactone oxidase. It is also not stored well in our body due to its high water solubility. Therefore, daily intake through diet and supplements is essential.

The recommended dietary intake of vitamin C is 40 mg per day (NHS, 2020) and this can be obtained from a variety of different foods and supplements such as:

• Citrus fruits (58 mg per 100 g of vitamin C)
• Peppers (100 - 200 mg per 100 g of vitamin C)
• Strawberries (58 mg per 100 g of vitamin C)
• Brussel sprouts (85 mg per 100 g of vitamin C)
• Broccoli (89 mg per 100 g of vitamin C)

Vitamin C Deficiency

When the amount of vitamin C ingested is consistently lower than the daily recommended intake, signs of vitamin C deficiency occur, in severe cases this is referred to as scurvy and presents with the following symptoms (NHS, 2020):

• Lethargy
• Irritability and depression
• Severe joint or leg pain
• Swollen bleeding gums
• Development of red or blue spots and skin that bruises easily

Vitamin C deficiency is a relatively rare condition, however, it can present in patients with certain risk factors such as: older males, low physical activity, smoking, alcoholism and low health literacy. People within these groups either have poor diets, reducing the amount of vitamin C ingested, or factors which increase oxidative stress on the body (e.g. smoking).

Benefits of Vitamin C

Vitamin C is a critical component for many bodily functions, with scientific evidence backing these four benefits:

1. Improves iron absorption: Iron exists in two forms, haem (found in animal products) and non-haem (found in plant based foods). Non-haem iron is not readily absorbed during digestion. Simultaneous administration of vitamin C and iron leads to chemical reduction of non-haem iron, increasing absorption and reducing diseases associated with iron deficiency, such as anaemia (Kristensen, 2005).
2. Maintains collagen production: Vitamin C (in the ascorbate form) has an enzymatic role in the production of collagen, the most abundant protein in the body and a major component of connective tissues that make up several parts of the body, including tendons, ligaments, muscle and skin. Therefore, ensuring adequate vitamin C levels maintains the integrity of connective tissue (Boyera, 1998 and DePhillipo, 2018).
3. Improves immune function: Vitamin C facilitates the bodies immune defences by protecting against oxidative stress (through its actions as an antioxidant), and by enhancing the generation of reactive oxygen species in immune cells, aiding microbial killing (Carr, 2018). There is little evidence to support vitamin C’s role in the prevention of viral respiratory viruses, however, some studies show that it can shorten their duration (Ran, 2018).
4. Reduces cholesterol levels: Studies have shown significant links between vitamin C supplementation and a reduction in LDL cholesterol and triglycerides. It is thought that this occurs through inhibition of oxidative modification of LDL’s, preserving the bodies ability to get rid of LDL cholesterol through catabolic pathways (breakdown of LDL into smaller molecules). A reduction in LDL may help reduce the risk of atherosclerosis and subsequently, coronary heart disease (McRae, 2008).

Vitamin C Supplements and their Differences

Vitamin C is predominantly transported through the intestines via transporter proteins. Typically, doses between 200 to 400 mg per day in healthy adults are enough to “saturate” transport of vitamin C into the body - meaning that taking doses beyond 400 mg results in less effective absorption.

Vitamin C can be obtained from food and supplements and it was shown that little difference exists between natural and synthetic forms in regards to biological activities (Carr, 2013). A number of formulations exist, each with their own

• Mineral ascorbates: Mineral salts of vitamin C are often used due to their reduced acidity, with sodium ascorbate and calcium ascorbate being the most common. Note that sodium ascorbate may not be suitable for patients on low sodium diets due to its high sodium content (Michels, 2018).
• Vitamin C with metabolites: This formulation is commonly known as Ester-C, and contains vitamin C (in the calcium ascorbate form) with its metabolites (dehydroascorbic acid, calcium threonate, xylonate and lyxonate). These metabolites are added with the intention of increasing oral bioavailability. A recent study found no significant difference in plasma concentration between Ester-C and ascorbic acid, however, a favourable increase in leukocyte vitamin C concentration was observed 24 hours after Ester-C administration, highlighting improved vitamin C retention (Mitmesser, 2016).
• Ascorbyl palmitate: Is a vitamin C ester (do not confuse with Ester-C), meaning that it consists of ascorbic acid (vitamin C) linked to a fatty acid named palmitic acid. The result of this formulation is a fat soluble form of vitamin C. Ascorbyl palmitate is more commonly used in skin creams. Oral formulations also exist, but it is often thought that the ester is hydrolysed into ascorbic acid and palmitic acid in the digestive tract before being absorbed (Michels, 2018).
• Vitamin C with flavonoids: Flavonoids are water soluble pigments found in vitamin C rich foods. They act as antioxidants via direct scavenging of free radicals, and as a result, they have been theorised to spare the oxidation of vitamin C and prevent its breakdown, increasing oral bioavailability (Carr, 2013).
• Liposomal vitamin C: A liposome is a spherical vesicle which is composed of a phospholipid bilayer, similar in structure the the walls of our cells. Newer formulations of vitamin C have incorporated vitamin C in the core of these liposomes in order to protect the vitamin from degradation and to increase absorption in the body (liposomal delivery does not rely on traditional transporter proteins). One study showed that liposomal vitamin C provided better circulating concentrations of the vitamin than non-liposomal vitamin C formulations (both taken orally) (Davis, 2016).

Conclusions

• Humans can’t synthesis vitamin C, so it must be ingested daily through diet and/or supplements.
• Groups with either poor diets, reducing the amount of vitamin C ingested, or with factors that increase oxidative stress on the body are at higher risk of vitamin C deficiency.
• Vitamin C plays an important role in various physiological functions and benefits: iron absorption, collagen production, immunity and cholesterol metabolism.
• A number of formulations for oral vitamin C exist, all with the intention of improving oral bioavailability through different mechanisms.

References

Boyera, N., Galey, I., & Bernard, B. A. (1998). Effect of vitamin C and its derivatives on collagen synthesis and cross-linking by normal human fibroblasts. International journal of cosmetic science, 20(3), 151–158. https://doi.org/10.1046/j.1467-2494.1998.171747.x

Carr, A. C., & Maggini, S. (2017). Vitamin C and Immune Function. Nutrients, 9(11), 1211. https://doi.org/10.3390/nu9111211

Carr, A. C., & Vissers, M. C. (2013). Synthetic or food-derived vitamin C--are they equally bioavailable?. Nutrients, 5(11), 4284–4304. https://doi.org/10.3390/nu5114284

Davis, J. L., Paris, H. L., Beals, J. W., Binns, S. E., Giordano, G. R., Scalzo, R. L., Schweder, M. M., Blair, E., & Bell, C. (2016). Liposomal-encapsulated Ascorbic Acid: Influence on Vitamin C Bioavailability and Capacity to Protect Against Ischemia-Reperfusion Injury. Nutrition and metabolic insights, 9, 25–30. https://doi.org/10.4137/NMI.S39764

DePhillipo, N. N., Aman, Z. S., Kennedy, M. I., Begley, J. P., Moatshe, G., & LaPrade, R. F. (2018). Efficacy of Vitamin C Supplementation on Collagen Synthesis and Oxidative Stress After Musculoskeletal Injuries: A Systematic Review. Orthopaedic journal of sports medicine, 6(10), 2325967118804544. https://doi.org/10.1177/2325967118804544

Kristensen, M., Hels, O., Morberg, C., Marving, J., Bügel, S., & Tetens, I. (2005). Pork meat increases iron absorption from a 5-day fully controlled diet when compared to a vegetarian diet with similar vitamin C and phytic acid content. British Journal of Nutrition, 94(1), 78-83. doi:10.1079/BJN20051417

McRae M. P. (2008). Vitamin C supplementation lowers serum low-density lipoprotein cholesterol and triglycerides: a meta-analysis of 13 randomized controlled trials. Journal of chiropractic medicine, 7(2), 48–58. https://doi.org/10.1016/j.jcme.2008.01.002

Michels, A. J. (2018). Vitamin C. Micronutrient Information Center. Oregon State University. Available at: https://lpi.oregonstate.edu/mic/vitamins/vitamin-C

Mitmesser, S. H., Ye, Q., Evans, M., & Combs, M. (2016). Determination of plasma and leukocyte vitamin C concentrations in a randomized, double-blind, placebo-controlled trial with Ester-C(®). SpringerPlus, 5(1), 1161. https://doi.org/10.1186/s40064-016-2605-7

NHS. (2020) Vitamin C: Vitamins and Minerals. Available at: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-c/

Ran, L., Zhao, W., Wang, J., Wang, H., Zhao, Y., Tseng, Y., & Bu, H. (2018). Extra Dose of Vitamin C Based on a Daily Supplementation Shortens the Common Cold: A Meta-Analysis of 9 Randomized Controlled Trials. BioMed research international, 2018, 1837634. https://doi.org/10.1155/2018/1837634