Your Expert Guide to Vitamin C

assortment of healthy fruits with vitamin c and multivitamins

The immune system is a sophisticated host defense system composed of several types of proteins, cells, organs, and tissues.

Its primary directive -- maintaining “watch” throughout the body for foreign invaders looking to wreak seven kinds of hell. When identified, the immune system kicks into gear, mounting a complex attack on the invaders.

Given recent events, heightened awareness has been placed not only on shoring up one's current immune system but how to improve its function (if possible).

Today, we begin our deep-dive into immune system supplementation with a look at the most popular over-the-counter remedy used to fight the common cold -- Vitamin C.

What is Vitamin C?

Vitamin C, also known as L-ascorbic acid, is an essential water-soluble vitamin that is naturally present in certain foods, such as oranges or strawberries.

It can also be used as an ingredient in various dietary supplements (including multivitamins and greens formulas) as well as certain fortified foods (breakfast cereals, protein bars, etc.)

The body contains between 300-2000mg of vitamin C, with the highest levels being found within leukocytes, brain, adrenal glands, and eyes. Lower levels of the essential vitamin are found in red blood cells, plasma, and saliva. <1>

What Does Vitamin C Do?

As an essential vitamin (and given the fact that it's contained within a vast array of tissues in the body), vitamin C plays several important roles in the body.

For starters, vitamin C is involved in the production of collagen, L-carnitine, and certain neurotransmitters (including dopamine and serotonin). <1>

It’s also involved in protein metabolism. <2>

Perhaps its most notable role is as an antioxidant in the body, where it helps combat the damaging effects of free radicals and oxidative stress. Vitamin C may also help regenerate other antioxidants within the body, such as vitamin E. <1>

Vitamin C also plays a vital role in immune function <4> and the absorption of nonheme (plant-derived) iron. <4>

Additionally, since vitamin C is structurally similar to glucose, it can replace glucose in various chemical reactions, and it can prevent the non-enzymatic glycosylation of protein. <3>

Deficiencies in the vitamin are known to cause scurvy, a condition characterized by fatigue, fragile capillaries, and systemic connective tissue weakness.

Benefits of Vitamin C

Supports Brain Development & Function

Vitamin C serves several critical roles in the growth, development, and function of the brain.

More specifically, vitamin C scavenges reactive oxygen species, limiting neuroinflammation.

It also modulates different neurotransmitter systems in the brain, including cholinergic, dopaminergic, and glutamatergic.

Vitamin C even contributes to the formation of new blood vessels in the brain, a process known as angiogenesis. <5>

Lastly, vitamin C also stimulates the expression of brain-derived-neurotrophic-factor (BDNF). This essential brain protein supports the survival of existing neurons and promotes the growth and differentiation of new neurons and synapses. <6>

Supports Lung Health

Lung levels of vitamin C are up to 30x that found in the plasma. <7>

Research indicates that even a single dose of vitamin C may be useful in defending against oxidative stress in the lungs. <7>

Additional studies using doses of vitamin C ranging from 500-2000mg / day halved the incidence of respiratory symptoms after short-term heavy physical stress. <8,9>

Supports Mitochondrial Function

Mitochondria are the “nuclear reactors” within cells that generate usable energy (ATP) to power the various functions of the cell.

Vitamin C stimulates mitochondrial function in three ways<10>:

  • Decreasing production of reactive oxygen species (ROS)
  • Boosting the activity of manganese superoxide dismutase/SOD2 and glutathione peroxidase (two powerful antioxidants)
  • Modifying the activity of the electron transport chain

Supports Bone Health

Vitamin C is required for optimal bone development.

Furthermore, research has noted a positive link between levels of Vitamin C and bone health, as evidenced by bone mineral density (BMD), bone turnover, and fracture probability. <11>

Regular use Vitamin C supplements, alongside hormone replacement therapy and calcium supplements, have been shown to improve bone mass in postmenopausal women. <12>

Supports Collagen Production

As we mentioned above, Vitamin C is critical to collagen production.

In case you weren’t aware, collagen is the primary structural protein in the body, responsible for the formation of skin, bones, tendons, ligaments, cartilage, and blood vessels. <13>

Supports Immune System Function

Vitamin C serves a vital role in the proper functioning of the immune system. Due to this, several studies have been carried out to investigate whether or not vitamin C supplementation may help reduce the onset, severity, or duration of certain ailments.

To date, supplementation with Vitamin C has been shown to:

  • Improve the functioning of various white blood cell types <14>
  • Reduce the replication of certain viruses <13>
  • Decrease duration and severity of the common cold <15>
  • Decrease duration and severity of respiratory infections <16>
  • Reduced the incidence of colds during periods of extreme physical stress <17>
  • Decrease the incidence of pneumonia <18>

May Help Limit Inflammation

Vitamin C is a powerful antioxidant that limits reactive oxygen species production, which helps combat oxidative stress and inflammation.

Furthermore, vitamin C also is noted to inhibit inflammatory cytokines. <19>

Various studies have found that vitamin C supplementation may help lower inflammation in persons with diabetes, hypertension (high blood pressure), and obesity. <3>

Best Sources of Vitamin C

One of the great things about vitamin C is that it can readily be found in several foods common to the diet.

Here is a list of foods particularly rich in vitamin C:


mg Vitamin C per serving

% Daily Value

Red Bell Pepper (½ cup)



Orange (1 medium)



Grapefruit Juice (6 oz)



Kiwi (1 medium)



Green Bell Pepper (½ cup)



Strawberries (½ cup)



Brussels sprouts (½ cup)



Grapefruit (½ medium)



Broccoli (½ cup)



Tomato (1 medium, raw)



Recommended Intake

Current recommendations for daily intake of Vitamin C are <20>:

  • 75 mg/day for women
  • 90 mg/day for men

Pregnant or lactating women may be advised to obtain at least 125 mg/day.

As a water-soluble vitamin, Vitamin C is not retained into the body, nor does it accumulate in various tissues for storage as the fat-soluble vitamins do. As such, the regular intake of relatively high quantities is suggested. Excess vitamin C is immediately eliminated through urine. <21>

Research indicates that intakes between 250-400mg per day are needed to saturate vitamin C concentrations in white blood cells and blood and white blood cells. <13,22>

The tolerable upper intake level is stated to be 2,000mg (2 grams) per day for adults.

It’s worth noting, however, that higher doses have been used in research trials with no apparent adverse side effects. <14>

Still, we do not recommend exceeding the tolerable upper intake level unless expressly directed to by a medical professional.

Steel Multi-V™ contains 100mg Vitamin C (as ascorbic acid) in every serving.

Natural vs. Synthetic Vitamin C

There’s a great debate between the efficacy and bioavailability of vitamins and minerals that are naturally present in food versus those that are added to dietary supplements and functional/fortified foods.

The truth is that it depends on what nutrient you’re talking about and what form that nutrient is in.

The current body of evidence indicates that there are no differences between synthetic and natural Vitamin C, regardless of the subject population. <23>

Researchers have also noted that any small differences observed between synthetic and natural vitamin C are transient and have a minimal physiological impact. <23>


Vitamin C is an essential water-soluble vitamin found naturally in food and added to several dietary supplements and fortified foods.

It is involved in a vast array of biological processes, including the formation of collagen, neurotransmission, antioxidant defense, and immune system function.

Studies to date note that vitamin C supplementation may help reduce the duration and severity of the common cold and respiratory infections.

Some of our favorite foods high in vitamin C are red bell pepper, oranges, strawberries, and kiwi.

Diet should always be the first choice when it comes to getting insufficient amounts of micronutrients.

But, we all have those days when we come up a bit short.

In these times, it helps to have a quality multivitamin supplement (such as Steel Multi-V™) and/or greens supplement (like Steel Greens™) to “fill in the occasional gaps.”


  1. Jacob, R. A., & Sotoudeh, G. (2002). Vitamin C function and status in chronic disease. Nutrition in Clinical Care : An Official Publication of Tufts University, 5(2), 66–74.
  2. Carr, A. C., & Frei, B. (1999). Toward a new recommended dietary allowance for vitamin C based on antioxidant and health effects in humans. The American Journal of Clinical Nutrition, 69(6), 1086–1107.
  3. Ellulu MS, Rahmat A, Patimah I, Khaza'ai H, Abed Y. Effect of vitamin C on inflammation and metabolic markers in hypertensive and/or diabetic obese adults: a randomized controlled trial. Drug Des Devel Ther. 2015;9:3405–3412. Published 2015 Jul 1. doi:10.2147/DDDT.S83144
  4. Gershoff SN. Vitamin C (ascorbic acid): new roles, new requirements? Nutr Rev 1993;51:313-26.
  5. Hansen SN, Tveden-Nyborg P, Lykkesfeldt J. Does vitamin C deficiency affect cognitive development and function?. Nutrients. 2014;6(9):3818–3846. Published 2014 Sep 19. doi:10.3390/nu6093818
  6. Acheson A, Conover JC, Fandl JP, DeChiara TM, Russell M, Thadani A, Squinto SP, Yancopoulos GD, Lindsay RM (March 1995). "A BDNF autocrine loop in adult sensory neurons prevents cell death". Nature. 374(6521): 450–53
  7. Hemilä H. The effect of vitamin C on bronchoconstriction and respiratory symptoms caused by exercise: a review and statistical analysis. Allergy Asthma Clin Immunol. 2014;10(1):58. Published 2014 Nov 27. doi:10.1186/1710-1492-10-58
  8. Hemilä H. Vitamin C and common cold incidence: a review of studies with subjects under heavy physical stress. Int J Sports Med. 1996;17:379–383. doi: 10.1055/s-2007-972864
  9. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;1:CD000980.
  10. Valdecantos, M. P., Perez-Matute, P., Quintero, P., & Martinez, J. A. (2010). Vitamin C, resveratrol and lipoic acid actions on isolated rat liver mitochondria: all antioxidants but different. Redox Report : Communications in Free Radical Research, 15(5), 207–216.
  11. Chin, K.-Y., & Ima-Nirwana, S. (2018). Vitamin C and Bone Health: Evidence from Cell, Animal and Human Studies. Current Drug Targets, 19(5), 439–450.
  12. Morton, D.J., Barrett‐Connor, E.L. and Schneider, D.L. (2001), Vitamin C Supplement Use and Bone Mineral Density in Postmenopausal Women. J Bone Miner Res, 16: 135-140. doi:10.1359/jbmr.2001.16.1.135
  13. Aguirre R, May JM. Inflammation in the vascular bed: importance of vitamin C. Pharmacol Ther. 2008;119(1):96–103. doi:10.1016/j.pharmthera.2008.05.002
  14. Hemilä H, Louhiala P. Vitamin C may affect lung infections. J R Soc Med. 2007;100(11):495–498. doi:10.1177/014107680710001109
  15. Gorton, H. C., & Jarvis, K. (1999). The effectiveness of vitamin C in preventing and relieving the symptoms of virus-induced respiratory infections. Journal of Manipulative and Physiological Therapeutics, 22(8), 530–533.
  16. Constantini, N. W., Dubnov-Raz, G., Eyal, B.-B., Berry, E. M., Cohen, A. H., & Hemila, H. (2011). The effect of vitamin C on upper respiratory infections in adolescent swimmers: a randomized trial. European Journal of Pediatrics, 170(1), 59–63.
  17. Johnston CS, Barkyoumb GM, Schumacher SS. Vitamin C supplementation slightly improves physical activity levels and reduces cold incidence in men with marginal vitamin C status: a randomized controlled trial. Nutrients. 2014;6(7):2572–2583. Published 2014 Jul 9. doi:10.3390/nu6072572
  18. Hemila, H., & Douglas, R. M. (1999). Vitamin C and acute respiratory infections. The International Journal of Tuberculosis and Lung Disease : The Official Journal of the International Union against Tuberculosis and Lung Disease, 3(9), 756–761.
  19. Yan H, Wang H, Zhang X, Li X, Yu J. Ascorbic acid ameliorates oxidative stress and inflammation in dextran sulfate sodium-induced ulcerative colitis in mice. Int J Clin Exp Med. 2015;8(11):20245–20253. Published 2015 Nov 15.
  20. Harrison FE. A critical review of vitamin C for the prevention of age-related cognitive decline and Alzheimer's disease. J Alzheimers Dis. 2012;29(4):711–726. doi:10.3233/JAD-2012-111853
  21. Fernando, D., Patricia, L., Pablo, Q., & M, J. A. (2014). Vitamin C in the Treatment and / or Prevention of Obesity, 367–379.
  22. Harrison FE. A critical review of vitamin C for the prevention of age-related cognitive decline and Alzheimer's disease. J Alzheimers Dis. 2012;29(4):711–726. doi:10.3233/JAD-2012-111853
  23. Carr AC, Vissers MC. Synthetic or food-derived vitamin C--are they equally bioavailable?. Nutrients. 2013;5(11):4284–4304. Published 2013 Oct 28. doi:10.3390/nu5114284

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