There has been a lot of talk about whether vitamin C will help prevent or treat COVID-19. To date, the safety and efficacy of vitamin C has not been established for the prevention or treatment of COVID-19.

However, there has been quality studies on the role of vitamin C and common colds.  

Vitamin C Supplementation

Vitamin C is an essential water-soluble vitamin in our diets.  It acts as an antioxidant – this means it plays a role in our immune functions and protection against infections.  Vitamin C is also import for the synthesis of hormones, collagen, and neurotransmitters.

Vitamin C in your Diet

The most common foods that contain vitamin C include:

  • Citrus fruits like oranges or grapefruit
  • Strawberries
  • Peppers
  • Tomatoes
  • Potatoes
  • Broccoli, cauliflower or cabbage
  • Fortified juices or foods

It doesn’t take a lot of food to reach the recommended intake of vitamin C daily.  As little as ¾ cup of orange juice or ½ cup of strawberries can give you 50% of what is required to prevent deficiency.   The average adult male requires 90mg of vitamin C per day.  The average adult female requires 75mg of vitamin C per day.  

By following Canada’s Food Guide and aiming for half your plate to be vegetables and fruits, you will have more than enough vitamin C in your diet.

Infants being fed breast milk or formula receive adequate vitamin C.

Vitamin C and the Common Cold

Cochrane review published in 2013 has summarized the evidence for vitamin C in preventing and treating the symptoms of the common cold.

Unfortunately, supplementing vitamin C beyond 200mg per day does not reduce the incidence of the common cold in the general population.  Supplementing vitamin C may reduce the duration of a common cold, but these results are not consistently found in studies. Starting vitamin C after symptoms of a cold start shows no benefit.

High Doses of Vitamin C

Vitamin C taken in excess will generally not have any toxic side effects.  Because it is water soluble, your body will excrete any vitamin C that it does not require.  

Most common side effects may include diarrhea, nausea, or abdominal cramps.  

A more rare side effect of high doses of vitamin C is kidney stones.  This is more likely to occur in patients with kidney disease or in children under the age of 2 if taking high doses.

This post was co-authored by Stephanie Liu, MD, MSc, CCFP, BHSc and Erin Manchuk, BScPharm, BCGP.