Vitamin C and immune health

Vitamin C or ascorbic acid has many health benefits from increasing iron absorption to supporting detox pathways. As a powerful anti-oxidant, Vitamin C improves lipid profile and is linked to reducing atherosclerosis, overall reducing risk for heart disease. Of the many benefits, it is well known that vitamin C supports the immune health in several ways.

Vitamin C deficiency can make you susceptible to infection by viruses and other pathogens.  In turn, the inflammation and other metabolic requirements caused by the infection, will further reduce vitamin C levels.

Some studies show that taking vitamin C supplement does not appear to prevent or reduce the number of colds, though lower number of colds were seen in physically active people taking at least 200 mg of vitamin C, cutting the risk by half. Even if research findings are mixed in the role of daily vitamin C supplementation to prevent colds, several studies have shown that taking large doses of vitamin C at the start of a cold reduces the duration and intensity of the symptoms.

Food sources of vitamin C

Food sources of vitamin C

When talking about vitamin C, most often you think of citrus fruits. See the list below for some of the common foods that contain vitamin C and the amounts

FoodMilligrams per serving
Guava, 1 medium126
Red pepper, raw, 1/2 cup95
Orange juice, 3/4 cup93
Orange, 1 medium70
Grapefruit juice, 3/4 cup70
Kiwi fruit, 1 medium64
Green pepper, raw, 1/2 cup60
Broccoli, cooked, 1/2 cup51
Strawberries, sliced, 1/2 cup49
Brussels sprouts, cooked, 1/2 cup48
Grapefruit, 1/2 medium39
Broccoli, raw, 1/2 cup39
Tomato juice, 3/4 cup33
Cantaloupe, 1/2 cup29
Cabbage, cooked, 1/2 cup28
Cauliflower, 1/2 cup26
Tomato, 1 medium17
Table of selected food sources of vitamin C

The recommended dietary allowance (RDA) for vitamin C is 75mg for women and 90mg for men. Eating a variety of fruits and vegetables daily from the list above should be adequate to meet the recommended daily allowance. But during times when additional vitamin C is required to further support immune health such as the start of cold , vitamin C supplementation may be appropriate.

How much Vitamin C supplement can I take?

Most study findings are based on vitamin C dosage of 1-2 grams per day for adults, in divided dosages. Some studies use even higher amounts.  The tolerable upper intake level for vitamin C is 2000mg for adults, both men and women.  If you take vitamin C supplement to reduce cold symptoms, Research studies show that it is most effective when taken within 24 hours of symptom onset and for a total of at least 5 days.

Ascorbic acid is the most common form of vitamin C supplement available. Some of the common side effects when not well tolerated or taken in excess are nausea, upset stomach and loose stools.

For people with sensitive gastrointestinal system, if the naturally acidic, ascorbic acid form of vitamin C is not well tolerated, buffered vitamin C supplement is a better alternative. Liposomal vitamin C is another form that is highly bioavailable with minimal gastrointestinal side effects.

Who should not take vitamin C supplements?

As vitamin C can increase iron absorption, vitamin C supplement should not be taken without talking to your Physician, if you have iron storage disease. Certain medications and chemotherapy drugs have potential of interacting with vitamin C, so discuss with your physician prior to taking the supplement.

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The information and other content provided in this blog are for information purpose only, and not intended and should not be considered as medical advice. If you have a medical concern, you should consult with your health care provider before you make any changes to your diet or lifestyle.


  • Hemilä H. Vitamin C and Infections. Nutrients. 2017;9(4):339. Published 2017 Mar 29. doi:10.3390/nu9040339
  • Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. 2017;9(11):1211. Published 2017 Nov 3. doi:10.3390/nu9111211
  • Bucher A, White N. Vitamin C in the Prevention and Treatment of the Common Cold. Am J Lifestyle Med. 2016;10(3):181-183. Published 2016 Feb 9. doi:10.1177/1559827616629092
  • Vitamin C, Fact sheet for Health professionals by Office of Dietary supplements, NIH, updated February 27, 2020. https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/