The body of research examining the relationship between vitamin D and COVID-19 is growing. Now, a study published recently confirms a correlation between low vitamin D levels and SARS-CoV-2 infection, and health professionals are theorizing whether vitamin D supplementation could increase the effectiveness of a COVID-19 vaccine.

Key Findings

"Vitamin D Status in Hospitalized Patients with SARS-CoV-2 Infection" appeared in The Journal of Clinical Endocrinology & Metabolism last month, confirming a relationship between low vitamin D and hospitalization due to COVID-19. The study's key findings are:

  • Serum 25OHD was significantly lower in hospitalized COVID-19 patients than population-based controls of similar age and sex
  • Vitamin D levels were remarkably low in male patients hospitalized for COVID-19
  • There was no association between vitamin D level and severity of infection as measured by admission to ICUs, need for mechanical ventilation, or mortality

Study Methods

The current study was a retrospective case-control study with 216 COVID-19 patients and 197 population-based controls. The researchers measured Serum 25-hydroxyvitamin D (25OHD) in both groups.

Case-control studies are particularly useful for studying outbreaks. They enable the researcher to determine if a given outcome, in this case, hospitalization for COVID-19, is related to a particular exposure, like low vitamin D levels.

A Growing Body of Research Points to Vitamin D Levels

Other researchers have found a connection between vitamin D levels and COVID-19 infections.

For example, Meltzer and colleagues found that "testing positive for COVID-19 was associated with increasing age (up to 50 years), non-White race, and likely vitamin deficient vitamin D status." COVID-19 rates were predicted at 21.6% in the vitamin D deficient group compared to 12.2% in the sufficient group.

Two months ago, Kaufman, Niles, Kroll, Bi, and Holick demonstrated that testing positive for COVID-19 was inversely associated with circulating vitamin D levels. In other words, there was a significant relationship between low vitamin D levels and positive COVID-19 test results. The association they found "persisted across latitudes, races/ethnicities, both sexes, and age ranges."

The link between vitamin D and respiratory problems is nothing new, so it is not surprising that there's a genuine relationship between vitamin D insufficiency and COVID-19 infection.

Will Vitamin D Come to the Rescue?

Now, the question is, can adequate vitamin D levels work to our advantage? Can sufficient levels of the vitamin be used to either improve COVID-19 outcomes or increase a COVID-19 vaccine's effectiveness? Future research will undoubtedly attempt to answer these questions.

It's not a bad idea to get your vitamin D level checked, in the meantime, and until we know more, especially if you live in the northern hemisphere where there is insufficient sunlight between November and March for vitamin D synthesis in the body.

The Mayo Clinic recommends that children up to twelve months of age receive 400 IU of vitamin D, 600 IU for those between 1 and 70, and 800 IU for people older than 70.

You will find vitamin D in fatty fish (e.g., salmon), fortified products (e.g., orange juice, cereals), cheese, and egg yolks, among other items.

Supplementation may help prevent vitamin D deficiency, but speak to your doctor before supplementing with vitamin D.