In a sea of depressing headlines, the link between healthy vitamin D levels and reduced COVID-19 severity stands out as one of the most promising and positive stories about the pandemic.
Many different lines of evidence have found that healthy vitamin D levels appear to reduce the risk of contracting or becoming seriously ill with COVID-19. An observational study published in July 2020 found that low vitamin D predicted both COVID-19 infection and subsequent hospitalization. And a pilot trial gave vitamin D to hospitalized patients and found that they were less likely to require admission to the ICU.
Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases and lead member of the White House’s Coronavirus Task Force, has recommended that Americans take note of their vitamin D status:
At this stage, randomized, controlled trials are needed to clarify whether vitamin D actually causes better COVID-19 outcomes, but it’s a good idea to test your vitamin D levels anyway. If you do have a deficiency, you’ll want to remedy it. Plus, the evidence we do have about the link between healthy vitamin D levels and milder COVID-19 is promising.
What is vitamin D?
Vitamin D is an essential nutrient. Often called the sunshine vitamin, vitamin D is manufactured by the body in response to UVB rays from sunlight.
However, in the winter months, and especially at northern latitudes, it can be much more difficult to get enough vitamin D from the sun alone. That’s why many health agencies recommend supplementing with vitamin D during the winter.
Vitamin D is an important nutrient, yet deficiency is prevalent in the US. A 2018 analysis found that approximately 39% of Americans were deficient in vitamin D. People of Hispanic or African-American descent were more likely to be deficient, because increased pigment in the skin makes it harder for the body to manufacture the vitamin from sunlight.
Vitamin D symptoms
The symptoms of vitamin D deficiency in adults can include:
- Muscle weakness
- Slow healing wounds
- Back pain
- Hair loss
- Depression and other mood problems
- Bone & joint pain
Researchers have long been aware that sufficient vitamin D levels support a healthy immune system. But could the sunshine vitamin also impact the way the body handles infection with SARS-CoV-2, the virus causing COVID-19?
Vitamin D and COVID-19: what’s the link?
Early research suggests there is a promising link between healthy vitamin D levels and better COVID-19 outcomes. However, the reason for that link, and whether vitamin D actually causes better outcomes, is still up for debate.
Because the coronavirus pandemic started relatively recently, there simply is not much research available. With each passing month, more and more evidence becomes available about COVID-19.
Because of insufficient evidence, the NIH currently does not recommend for or against vitamin D in the prevention or treatment of COVID-19. However, President Trump was given vitamin D as part of his treatment cocktail when he became infected with the coronavirus in early October 2020, and Dr. Anthony Fauci recommends it preventively.
Evidence about the link between vitamin D and COVID-19 is still mostly correlational, though causal evidence is beginning to mount.
There are other possible explanations for a correlation, like a third variable which affects both vitamin D levels and COVID-19 risk, a confounding factor that makes it look like vitamin D is affecting COVID-19, or even that COVID-19 itself reduces vitamin D.
What do studies say about vitamin D and COVID-19?
High-quality evidence from randomized controlled trials suggests vitamin D supplementation protects against respiratory tract infections.
A 2017 meta-analysis of 11,321 participants in 25 randomized controlled trials showed that vitamin D supplementation protected against acute respiratory tract infections.
Because COVID-19 results from a respiratory tract infection, it stands to reason that vitamin D supplementation may be protective, too.
ⓘ Update: A November 2020 preprint has reanalyzed the results of this study, and addresses some of the concerns about the study’s design. The authors conclude that worries about uneven distribution of comorbidities (the presence of co-existing diseases), as well as about sample size, are unfounded. The article concludes that the reduction in ICU admissions was caused by the Vitamin D intervention.
A pilot randomized controlled trial suggests vitamin D may reduce the severity of COVID-19.
An October 2020 pilot study conducted in Spain showed promising results.
One group was given 25-OH Vitamin D, which is the form of vitamin D found in the blood, plus the best treatment available. The control group was only given the best treatment available.
Only 2% of patients in the group given vitamin D had to be admitted to the ICU, while 50% of the control group required admission to the ICU.
The results should be interpreted with caution, however, as the sample size was low. In addition, the control group had more comorbidities than the treatment group, even though the patients were randomized. Regardless, the results are considered statistically significant.
A large observational study found a strong correlation between low vitamin D and COVID-19 infection and hospitalization.
A July 2020 observational study of over 7,800 patients in Israel found a strong correlation between low vitamin D levels and COVID-19 infection and hospitalization.
People with low blood levels of vitamin D were 1.45 times more likely to become infected with COVID-19.
Once infected, they were 1.95 times more likely to be hospitalized with COVID-19 than those with normal vitamin D levels.
Vitamin D deficiency predicts a higher COVID-19 incidence in different locales.
A September 2020 preprint study analysed vitamin D test results from 2010-2019, and compared this to rates of COVID-19.
They found a statistically significant correlation between vitamin D deficiency prevalence and COVID-19 incidence, in different areas.
Vitamin D could explain many of the risk factors for severe COVID-19.
A July 2020 article published in the Journal of Internal Medicine reported that many of the risk factors for severe COVID-19 were also associated with vitamin D deficiency. This provides further circumstantial evidence for a potential role of vitamin D deficiency in severe COVID-19.
Older age, male sex, obesity, diabetes, hypertension, and non-white ethnicity are all risk factors that predict a worse COVID-19 outcome. These are all also associated with vitamin D deficiency.
Should I monitor my vitamin D levels?
Even if the evidence is not currently conclusive, it seems like a good idea to monitor one’s vitamin D levels, and consider supplementing anyway.
Worst case, you’ve increased your levels of an essential nutrient that boosts your general health. Best case, you’ve reduced your chances of severe COVID-19 infection.
People can check their vitamin D levels with a simple blood test, which can either be ordered by a doctor or purchased privately.
However, Prassas also cautioned against taking this advice to the extreme.
The official recommendation from the NIH is about 600 IU per day for adults, however, people can safely take up to 4000 IU per day. Sometimes, a person needs more than the recommendation to remedy a deficiency. When in doubt, a doctor can help you find the right dosage.
While evidence about the link between vitamin D and COVID-19 is still inconclusive, what evidence we do have suggests healthy vitamin D levels may be protective against infection and serious illness.
Because vitamin D is an essential nutrient, and because vitamin D supplements are not considered to be risky, people should consider checking their vitamin D levels and supplementing if necessary.
The worst case is you’ve remedied a deficiency, and the best case is you’ve improved your chances of having mild COVID-19.
When asked what his conclusion was, Prassas had a simple message: consider checking up on your vitamin D levels and supplementing, even if the jury is still out.
“We need more randomized controlled trial studies in order to claim with certainty that low vitamin D is a poor prognostic factor for COVID-19. But mounting evidence is pointing in this direction. So, when taken properly (and not in excess), vitamin D supplements can really only do good.”