A new study has reignited a debate over the role of vitamin D in mitigating severe COVID-19 symptoms as researchers suggest those with a deficiency may be more likely to develop serious illness.
Leading infectious disease experts say that more in-depth research is needed to confirm whether vitamin D is directly associated with COVID-19 severity.
Vitamin D cannot prevent COVID-19 transmission all on its own, and experts say its crucial to speak to a doctor before seeking out supplements, as large doses can be harmful to your health.
In the report below, you'll learn: Is vitamin D actually beneficial against infections? And can Vitamin D alone prevent COVID-19?
Vitamin D's role in the prevention of the spread of COVID-19 has been long contested by many experts since the pandemic began, fueled by early chatter of alternative treatment methods back in 2020. But a new piece of research has once again reignited the public's interest in these supplements, as scientists highlight a possible association between vitamin D levels and the immune system's ability to fend off severe COVID-19 symptoms, particularly associated with the Omicron variant.
The small-scale study, which was organized by researchers in Israel and is based on data collected between April 2020 and February 2021, was recently published in PLOS ONE and presents a case that researchers say is "equally relevant" for Omicron spread as well. The data was collected from 253 people who were admitted to hospitals for treatment (at a time before vaccines were available) and was used to conclude that those who had a vitamin D deficiency were more likely to develop a severe or critical case of COVID-19, as compared to patients who had sufficient vitamin D levels within blood samples taken at the time of hospitalization. About half of those in the study were deficient in the vitamin.
Further links found within the new study suggest that those who were lacking vitamin D were 14 times more likely to experience severe COVID-19 complications, which the National Institutes of Health (NIH) define as someone likely needing a respirator to breathe — and in severe cases, those who experience respiratory failure, septic shock or multiple organ dysfunction. Those with a vitamin D deficiency were significantly more likely to die due to infections, the study found; 25.6% mortality rate versus just 2.3% for those who weren't lacking vitamin D.
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Some may come to the conclusion that making sure you get sufficient levels of vitamin D can help keep your immune system in top shape, but other experts are keen to point out that this study doesn't prove that vitamin D alone can save you from severe infection. Paul Spearman, M.D., director of the division of infectious diseases at Cincinnati Children's Hospital, tells Good Housekeeping that more research is needed to confirm whether vitamin D levels will be an indicator of how severe symptoms will be for someone impacted by COVID-19.
"We have to remember that an association doesn't mean causation — meaning, that other things going on in [those people] with low vitamin D levels may cause severe disease, and not the low vitamin D itself," he explains, adding that a randomized, controlled, double-blind study of vitamin D supplementation before COVID-19 infection would be needed for concrete proof. "This type of study is hard to do and requires enrolling a large number of patients."
Dr. Spearman adds that this isn't the first time that vitamin D has been considered in limited meta-analysis research to determine the role this nutrient plays in COVID-19 infections. Conflicting research suggests that low vitamin D levels don't "aggravate" COVID-19 risk or death, nor that upping vitamin D supplements in any given routine improves patients' health as they recover in the hospital, he says. A 2021 Nutrition Journal study concluded there wasn't an association between COVID-19 severity and vitamin D levels and a preprint of a study out of the University of Sao Paulo in Brazil suggests vitamin D supplements administered to hospitalized patients also didn't provide any recovery benefits.
But vitamin D is far from useless, and while its role in preventing or stemming the severity of a COVID-19 infection is still uncertain, Dr. Spearman adds that there are theoretical reasons behind why immune systems may be impacted if someone isn't sufficiently getting enough vitamin D.
Is Vitamin D beneficial against infections?
Nutrition experts have long established that vitamin D is essential for optimal bone health (as it helps absorb calcium) and that the nutrient aids muscle function in addition to being linked to a few other key bodily functions. Vitamin D levels are influenced by nutrition, certainly, as it can be partially sourced from food — things like fatty salmon, beef liver, egg yolks and Swiss cheese all contain ample vitamin D — but is often sourced naturally just by being outside. "The most well-known way to get your dose of vitamin D is exposing yourself to sunlight," says Stefani Sassos, MS, RD, CDN, a registered dietitian in the Good Housekeeping Institute, in an interview touting potential benefits of the supplement.
But evidence for vitamin D's role in boosting immunity overall isn't as clear, Dr. Spearman explains. "Vitamin D has been evaluated to help fight other respiratory infections — unfortunately, we don't have a clear answer here either, except that giving a single large dose isn't helpful at all," he says. "Meta-analyses of this question have been inconclusive."
This new study may add more weight to burgeoning evidence that there may be an association of low vitamin D levels correlated with severe disease, COVID-19 included. But if there is an immune-boosting benefit to be had, "it is with standard, low doses and not large doses," Dr. Spearman clarifies.
Experts from across fields of study, including Spearman and Sassos, agree that vitamin D supplements should be a consideration primarily if your doctor has detected you have low vitamin D levels in treatment. If news of this study has you curious about your own vitamin D intake, make it a point to discuss it with your doctor — but you're likely to have sufficient vitamin D coursing through your veins. Only 5% of Americans suffer from a severe vitamin D deficiency, per the NIH, and 18% have been noted to have "inadequate" levels which may or may not cause issues associated with aches, cramps, or muscle development, Sassos adds.
"If someone is detected by their doctor as having low vitamin D levels, they should receive supplementation with medical guidance," Dr. Spearman advises. "We should keep in mind that taking large doses of vitamin D is dangerous, and self-medicating can cause problems — including high blood calcium and kidney failure."
"Whereas excess of water-soluble vitamins are rapidly excreted through urine, fat-soluble vitamins like vitamin D are stored in the body for long periods of time and can pose a higher risk for toxicity if consumed in excess," Sassos adds.
Can taking Vitamin D prevent COVID-19?
Taking this study and conflicting research into account, and everything we know about how SARS-CoV-2 impacts both vaccinated and unvaccinated individuals, it's clear that vitamin D supplements alone cannot prevent COVID-19 transmission. Experts are continuing to examine how vitamin D may play a small role in lowering the risk of someone experiencing a severe sickness or dying after being infected. "For a normal, healthy person, the role of a low-dose, ongoing supplement in preventing severe COVID-19 is not yet certain," Dr. Spearman says.
The debate over vitamin D's role in helping bring an end to the pandemic is likely going to continue to be a topic of discussion, as experts are now conducting appropriately prospective, randomized and controlled studies of vitamin D supplementation. "We hope to have a more definitive answer from these trials, which can provide a higher level of evidence," he adds.
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Experts are agreed that the only role vitamin D may play in ending the pandemic may be partial and preventative in nature, versus an active solution after someone has become sick. "Supplementing vitamin D may play a role in treating patients, but the data is relatively weak at this time," Stuart Cohen, M.D., chief of infectious diseases at UC Davis Health, shared in a recent communications report. "It surely is not a way to treat COVID-19 in and of itself."
Talking to your doctor about vitamin D can be an effective way to make sure you're supporting your immune system with optimal nutrients across the board. It may also help you to consider that, in spite of discussion of alternative forms of prevention, current vaccines have demonstrated their effectiveness at preventing hospitalization and death stemming from COVID-19 infections.
The bottom line:
Getting enough vitamin D is a valid concern you should discuss with your doctor, especially if you are someone who may be disposed to inadequate or deficient levels of this essential nutrient. Experts have previously established that these at-risk individuals would benefit from discussing vitamin D supplements with a doctor:
Adults over the age of 65
People with clinical obesity
People diagnosed with liver disease, celiac disease, cystic fibrosis and/or Crohn's disease or ulcerative colitis
Those who experience limited sun exposure
Those with dark skin tones
Those enjoying a plant-based lifestyle
Your healthcare provider can order a blood test to examine your vitamin D levels, Sassos adds, and can help you figure out which supplements work best for you at the appropriate dosage.
"Taking vitamin D under medical supervision for those who have measured vitamin D deficiencies is warranted," Dr. Spearman adds. "[But] the best prevention of severe COVID-19 is certainly earned through vaccines, and the evidence here is undeniable."
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