If you’re like many of us, grasping for ways to protect yourself and your family during this vulnerable time has become a daily commitment. In doing so, you may have stumbled upon recommendations to take a vitamin D supplement for COVID-19 prevention. Many information outlets are promoting vitamin D as a lifesaving supplement during this time, and we’d like to present you with the facts and take a deep dive into this issue.

First, we know that vitamin D plays a key role in our immunity by boosting the function of immune cells, both T-cells and macrophages, and by regulating our immune response in preventing an excessive release of cytokines. In the case of COVID-19, too many cytokines, referred to as a “cytokine storm”, can lead to excessive inflammation in the lungs and sometimes death. Studies have shown that insufficient vitamin D levels are associated with an increased risk of infection and autoimmunity, and there are specific links between vitamin D deficiency and respiratory conditions, including asthma, respiratory infections, tuberculosis, and decreased lung function. We also know that vitamin D plays a role in shaping gut bacteria and intestinal epithelial cells, which can have meaningful impacts on the gut microbiota and immune health.

Studies have emerged within the last month that show a strong association between vitamin D deficiency and COVID-19 fatality. The most well done studies to date were featured in a Newsweek article, Does Vitamin D Deficiency Really Increase Risk of Death from COVID-19. An April 2020 study conducted out of the University of Southeastern Philippines measured vitamin D levels (serum 25(OH)D) in 212 COVID-19 patients, and then followed them throughout the course of their disease. Findings showed that those with deficient vitamin D serum levels were almost 20 times more likely to need critical care.

A second study looked at vitamin D levels and COVID-19 disease outcomes in 780 patients in Indonesia and found that those with insufficient serum vitamin D levels were more likely to die from COVID-19. While the first study did not adjust for confounding factors (patient characteristics that may explain why complications occurred, other than low vitamin D) – a huge drawback that takes away from the study’s findings – the Indonesian study adjusted for age, sex, and comorbidity (other illnesses or conditions the patient might have had), and still found a strong association between vitamin D status and disease outcome.

While these studies show a strong association between vitamin D deficiency and COVID-19 complications, experts stress that the findings do not prove a causal link between insufficient vitamin D levels and COVID complications. Therefore, it’s impossible to say at this time that low vitamin D causes COVID-19 complications or increases chances of mortality. While adjusting for age, sex, and comorbidity (as was done in the Indonesian study) is important, other confounding factors could be at play here; adequate vitamin D levels could mean a healthier diet, better access to healthcare, a history of regular exercise, and so on. So, it could be these other factors that lead to better COVID-19 outcomes, and not adequate vitamin D levels at all. More studies are needed to determine whether there is indeed a causal link. It’s also important to point out that the peer review process hasn’t vetted these studies, where experts dig deep into the research methodology and conclusions to identify weaknesses. It will be important to revisit these studies once that process is complete.

When it’s all said and done, if we do find that vitamin D deficiency is in fact associated with severe COVID-19, this association still doesn’t tell us whether or not vitamin D supplementation protects against COVID-19. And to be clear, no evidence points to vitamin D supplementation as a way to protect you from or cure yourself of COVID-19, especially for those with normal levels.

So, what do we recommend at this time? First and foremost, focus on the basic practices that we know support a strong immune system – eat lots of brightly colored vegetables and fruits, get plenty of sleep, manage your stress, exercise, and spend time outdoors. Second, since we know vitamin D plays an important role in immunity, practice natural ways to get plenty of vitamin D:

Food	Amount	% RDI
Cod liver oil, 1 tablespoon (15 ml)	1,360 IU / 34 mcg	227%
Salmon, cooked, 3 ounces (85 grams)	447 IU / 11 mcg	75%
Tuna, canned in water, 3 ounces (85 grams)	154 IU / 4 mcg	26%
Beef liver, cooked, 3 ounces (85 grams)	42 IU / 1 mcg	7%
1 large whole egg (D is found in yolk)	41 IU / 1 mcg	7%
1 sardine, canned in oil, drained	23 IU / 0.6 mcg	4%

If you think you might be vitamin D deficient, getting your vitamin D levels (also referred to as 25(OH)D) checked is a good idea. Signs of vitamin D deficiency can be non-specific and include frequent infections, unexplained fatigue, depression, bone and muscle pain, bone loss, and hair loss, while the risk factors for vitamin D deficiency include having dark skin, excessive body weight, and limited sun exposure. If your levels are below 30 ng/ml, supplementation is recommended. If your levels are between 30 and 50 ng/ml, no supplementation is necessary.

Studies do show that in those who are severely deficient, vitamin D supplementation can possibly help protect against respiratory infections. But this hypothesis has not been tested in COVID-19 patients and we have absolutely no evidence at this time that vitamin D supplementation is protective against the disease. In addition, it’s important to remember that even if you do decide a vitamin D supplement is right for you to maintain sufficient serum levels, nothing can compare to consuming a healthy diet and spending time outside in sunlight. So be sure to continue practicing these lifestyle habits alongside your supplement.