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Grapefruit and Vitamins

Immune System Supplementation


  • Contrary to popular belief, zinc supplementation has not been found to aid in preventing COVID-19. There is, however, some evidence for its use in the common cold. 

    • The majority of clinical trials show decrease in the duration of symptoms of common cold in those who used zinc lozenges 

  • Dietary sources: oysters, shellfish, liver, beef, lamb, pork, legumes, milk, wheat bran

    • Vegetarians and alcoholics are often at risk for zinc deficiency

  • Dosing:

    • Limit is 40 mg/day elemental zinc for general supplementation

      • Take with food to minimize nausea and vomiting

    • Common cold dosing >75 mg/day elemental zinc

      • 9-24 mg lozenges taken every 2 hours while awake (at least 75 mg/day), starting within 48 hours of symptom onset

  • Side effects: stomach upset


Vitamin C

  • While there is no strong evidence for its use in COVID-19, some experts suggest taking 200 mg/day to help prevent it. There is also some evidence for its use in the common cold. 

  • Dietary sources: citrus fruits and certain vegetables such as broccoli

  • Dosing:

    • Dependent on indication

      • Dose 200 mg/day for prevention of respiratory illness

    • Rarely exceed 400 mg/day

      • However, doses of 2 grams daily have shown benefit in decreasing duration of the common cold, with doses going as high as 3 grams daily for temporary usage

  • Side effects: Nausea, stomach cramps, diarrhea, kidney stones

Vitamin D

  • Vitamin D deficiency can negatively impact immune system function

  • Dietary sources: fatty fish, mushroom, sun exposure

  • Dosing:

    • 600-800 IU/day

  • Side effects (with excessive use): high calcium, kidney stones



  • Contrary to popular belief, there is no evidence that elderberry aids in preventing COVID-19. There is, however, some evidence for use in influenza, and limited evidence for use in the common cold.

  • Dosing: 

    • Influenza: 15 ml of extract four times daily for 3-5 days

  • Side effects: GI upset

Stop into Cedar Springs Pharmacy today for more information, or to pick up some of these immune system supplements!

Information compiled from Natural Medicines database by Erin Drylie, Pharm.D Candidate 2023, Ferris State University.

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