Using Vitamin C and D to Boost Your Immune System

Using Vitamin C and D to Boost Your Immune System

Vitamins C, D and the mineral zinc have been making headline news in 2020 as people look for ways to strengthen immune defenses against respiratory infections. While media can often unfairly represent important nutrients, this trio has recently been represented in a positive light, and for good reason. All three have been shown to support the activity and function of the cells within the immune system.


Why are vitamins C and D important?

Vitamin C has long been recognized as an important antioxidant to support the immune system and regular use has been shown to shorten the duration of colds and reduce their severity.1,2 Vitamin D, once most commonly associated with its vital role in bone health, has gained in popularity in more recent years with an association based on a significant amount of research showing it too is a valuable asset to the immune system.3-5 Both these vitamins’ role in human health continue to impress researchers.

Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases, recommends supplementing with vitamins D and C to support immune health. "If you're deficient in vitamin D, that does have an impact on your susceptibility to infection,” said Dr. Fauci in a recent interview. So, how do you know if you’re deficient? A simple 25-Hydroxy Vitamin D Blood Test can tell you your levels, and the test is available in most states without requiring a doctor visit or insurance. Life Extension has long advocated an optimal vitamin D blood level between 50-80 ng/mL.


How much vitamin C and D per day?

Functional medicine experts often recommend more than the 15 mcg (600 IU) RDA of vitamin D daily in order to support optimal health. The RDA of vitamin C for adults is 75–90 mg for women and men, respectively, and slightly higher for smokers and pregnant or breastfeeding women. However, the Linus Pauling Institute recommends 200–400 mg of vitamin C per day. Even conventional medical experts like Dr. Fauci support supplementing with 1000 mg of vitamin C daily due to its antioxidant support.

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According to the 2015-2020 Dietary Guidelines, vitamins C & D, among other nutrients, are underconsumed by Americans. The guidelines go on to state that “of the underconsumed nutrients, calcium, potassium, dietary fiber and vitamin D are considered nutrients of public health concern because low intakes are associated with health concerns.” Life Extension generally suggests 5000 IU of vitamin D daily for most adults in order to support optimal levels.

Heart shape tray with lean protein and nutritious veggies and a stethoscope


Vitamin C and D food sources

Humans are unable to synthesize their own vitamin C and must obtain it from food and supplementing. Skin has the ability to manufacture vitamin D from sunlight but with limitations such as one’s age, skin color, geographic latitude and sunscreen use. Furthermore, food is often an unreliable way to obtain enough vitamin D required to reach and maintain optimal levels.

Heart shape tray with lean protein and nutritious veggies and a stethoscope

Vitamin D

  • Fatty fish such as salmon and trout
  • UV exposed mushrooms
  • Egg yolks
  • Fortified cereal, dairy and non-dairy milks
Heart shape tray with lean protein and nutritious veggies and a stethoscope

Vitamin C

  • Kiwi fruit
  • Citrus fruits
  • Strawberries
  • Broccoli
  • Peppers


Vitamin C and D considerations during the coronavirus pandemic

Vitamin C has been shown to actually lower time on a ventilator among critically ill patients in the ICU. This is important because there are long term negative effects from being on mechanical ventilation.

An interesting correlation is that African Americans and Hispanics are often found to be vitamin D deficient and these same groups are also disproportionally impacted by the coronavirus crisis.6,7 In fact, African Americans who are deficient in vitamin D tend to have more severe SARS-CoV-2 symptoms and a higher rate of mortality from it.7

Vitamin C’s role in the immune system

Vitamin C has been shown to support the immune system by several mechanisms:8

  1. Helps the activity of our immune cells
  2. Reduces inflammation caused by infections
  3. Creates and maintains protective tissue barriers such as those found in the lining of the airways of our lungs via collagen synthesis

How vitamin D benefits the immune system

Like vitamin C, vitamin D is useful when it comes to supporting the immune system; it too can help the activity of our immune cells and reduce inflammation caused by infection—this includes inflammation caused by inflammatory cytokines and “cytokine storm”.9,10 Vitamin D may also play a role in the prevention of autoimmune disease and acute respiratory infections.11

Vitamins C & D: The dynamic duo

From helping with the common cold to more advanced roles in health, such as being used as an IV treatment to reduce sepsis mortality, vitamin C remains an immune system superstar. And because vitamin D receptors are present in most tissues and cells within the body, including immune cells of course, it too has proven to be a tremendous asset to our health.


Note: Life Extension is not affiliated, associated, authorized, endorsed by, or in any way officially connected with Dr. Fauci or the National Institute of Allergy and Infectious Diseases.


Heart shape tray with lean protein and nutritious veggies and a stethoscope

About the Author:

Holli Ryan is a South Florida based Registered and Licensed Dietitian-Nutritionist. Holli believes that quality dietary supplements are an essential tool that have a variety of applications, from maintaining good health to managing chronic disease.


Article References

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  2. Colunga Biancatelli RML, Berrill M, Catravas JD, Marik PE. Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19). Front Immunol. 2020;11:1451.
  3. Jovic TH, Ali SR, Ibrahim N, et al. Could Vitamins Help in the Fight Against COVID-19? Nutrients. 2020;12(9).
  4. Poorna R, Biswal N. Respiratory infections: Role of Vitamin D and surfactant proteins A and D. Lung India. 2020;37(5):421-424.
  5. Kowalówka M, Główka AK, Karaźniewicz-Łada M, Kosewski G. Clinical Significance of Analysis of Vitamin D Status in Various Diseases. Nutrients. 2020;12(9).
  6. Vyas N, Kurian SJ, Bagchi D, et al. Vitamin D in Prevention and Treatment of COVID-19: Current Perspective and Future Prospects. Journal of the American College of Nutrition. 2020:1-14.
  7. Martín Giménez VM, Inserra F, Ferder L, García J, Manucha W. Vitamin D deficiency in African Americans is associated with a high risk of severe disease and mortality by SARS-CoV-2. Journal of human hypertension. 2020:1-3.
  8. Boretti A, Banik BK. Intravenous vitamin C for reduction of cytokines storm in acute respiratory distress syndrome. PharmaNutrition. 2020;12:100190.
  9. Bishop E, Ismailova A, Dimeloe SK, Hewison M, White JH. Vitamin D and immune regulation: antibacterial, antiviral, anti-inflammatory. JBMR Plus. 2020.
  10. Daneshkhah A, Agrawal V, Eshein A, Subramanian H, Roy HK, Backman V. Evidence for possible association of vitamin D status with cytokine storm and unregulated inflammation in COVID-19 patients. Aging clinical and experimental research. 2020:1-18.
  11. Charoenngam N, Holick MF. Immunologic Effects of Vitamin D on Human Health and Disease. Nutrients. 2020;12(7).