Vitamin D Supplementation

Function of Vitamin D

Some studies have indicated that vitamin D supplements can enhance immune response and protect against respiratory infections overall. Vitamin D supplements have also been shown to reduce mortality in older adults, who are most at risk for developing respiratory illnesses like COVID-19. Vitamin D maintains average blood concentrations of calcium and phosphorus in the body as well as supports bone health.

Risk Factors for Vitamin D Deficiency

  1. Failing to get at least 15 minutes of direct sun exposure daily.
  2. Being African American or dark-skinned
  3. Elderly
  4. Overweight or obese.

Types of Vitamin D

The two forms of vitamin D used in supplements are D2 (ergocalciferol) and D3 (cholecalciferol). D3 is the preferred form, as it is chemically similar to the form of vitamin D produced by the body and is more effective than D2 at raising the blood levels of vitamin D.


Depending on your blood levels, supplementing with 1,000–4,000 IU of vitamin D per day is typically sufficient for most people. However, those with low blood levels will often require much higher doses to increase their levels to an optimal range.
It is not recommended to take more than 2,000 IU daily in supplement form without the advice of a health care provider. If you’re interested in supplementing with vitamin D to enhance your overall immune response, consult your healthcare provider for information on proper dosing.

Normal Blood Level Range

Though recommendations on what constitutes an optimal vitamin D level vary, most experts agree that optimal vitamin D levels lie between 30–60 ng/mL (75–150 nmol/L). Low vitamin D levels are associated with an increased risk of respiratory diseases, decreased lung function, as well as viral and bacterial respiratory infections.


Evidence that vitamin D supplements reduce the risk of developing COVID-19 is lacking, but having healthy vitamin D levels can enhance immune health. Plus, vitamin D supplements may protect against respiratory infections in general. As the number of people with vitamin D deficiency continues to increase, the importance of this hormone in overall health and the prevention of chronic diseases is at the forefront of research.
Fobi Pharmacy Drug Information Provided by:
William Fobi, Pharm.D
Director of Clinical Pharmacy Services
Fobi Pharmacy; Ph: 562-630-5700