There is a “D” in Covid-19. But can a lack of Vitamin D make you more susceptible to the Covid-19 coronavirus? Well, some studies have suggested this possibility. However, before you rush to the store and start hoarding Vitamin D supplements like they were toilet paper, let’s “D”-construct the currently available evidence.

If you think that Vitamin D only has to do with bone health, you may be wondering what it could possibly have to do with Covid-19. After all, you may have a bone to pick with the virus but its main effects don’t seem to be on your skeleton. Well, studies have shown that Vitamin D may affect different components of your immune system and its response to infection. It may help modulate your lymphocytes and inflammation-producing chemicals like cytokines that are important components of your immune response to invading viruses.

This could potentially, possibly, perhaps be relevant for Covid-19 because badness may result when your immune system overreacts to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV2). As I’ve described previously for Forbes, since your immune system is not used to seeing the SARS-CoV2, your body’s defenses can act like someone experiencing something like sex for the first time. It can be a bit, ahem, quick on the trigger and start trying all kinds of random things, many of which don’t really work. Some of which may cause damage to the surroundings (your body, in the case of your immune response and your bedroom, in the case of sex). In some cases of Covid-19, the resulting “cytokine storm” can cause widespread damage to different organs and lead to death. Therefore, any way that your immune system can better regulate its own response could potentially be beneficial.

Back in 2017, the BMJ published a systematic review and meta-analysis of randomized, placebo controlled clinical trials that evaluated how Vitamin D supplementation may affect the risk of getting acute respiratory tract infections. The review returned 25 such trials. The combined results revealed that those who received Vitamin D supplementation had a 12% lower likelihood of getting an acute respiratory tract infection. Although the authors of this systematic review concluded that “Vitamin D supplementation was safe and it protected against acute respiratory tract infection overall,” a letter to the BMJ warned that people shouldn’t go overboard with these recommendations, that taking too much Vitamin D has it’s risk too. But more on this later.

Additionally, while this systematic review suggested that Vitamin D supplementation could be associated with a lower risk of respiratory tract infections, it still did not prove that it can prevent such infections. The review had its limitations, and not all individual studies have shown that Vitamin D supplementation is associated with an lower incidence of respiratory tract infections. The jury is still out. And it’s not all taking Vitamin D.


Even if Vitamin D were proven to offer some benefits against other respiratory tract infections, this SARS-CoV-2 ain’t your everyday respiratory virus. It’s continued to prove that it’s very different from adenoviruses, respiratory syncytial viruses (RSV), influenza viruses, and other more common viruses that can infect your respiratory tract. If respiratory viruses had Spice Girl names, SARS-CoV2 would be Scarily Unpredictable Spice. So what holds for other viruses may not hold for the SARS-CoV2.

What then can be said about Vitamin D and SARS-CoV2? Well, the little evidence that’s available for this new virus is, shall we say, quite in-D-rect. Existing studies have looked at possible correlations and associations, which do not prove cause and effect.

For example, a manuscript posted on MedRxivdescribed a study that analyzed data from Germany, South Korea, China, Switzerland, Iran, the U.K., France, Spain, Italy, and U.S. and found that 17.3% of those with severe Vitamin D deficiency had severe COVID-19 compared to 14.6% of those with normal Vitamin D levels. Keep in mind that posting a manuscript on MedRxiv doesn’t mean that the manuscript has undergone peer-review or will ever make it to an respected scientific journal. It simply meant that the authors had Internet access and were able to follow a set of instructions to upload the manuscript. In theory, one could post on such a platform a manuscript describing how teddy bears are the cause of all problems in the world.

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Then, there was the study published in the Irish Medical Journal, which showed that countries in Europe where older adults tended to have lower Vitamin D levels like Spain and Italy also tended to have higher Covid-19 coronavirus infection rates and mortality than those with higher Vitamin D levels like Norway, Sweden, and Finland. Simply showing such a correlation does not really prove much as many things could vary along with both Vitamin D levels and Covid-19 outcomes. As you can imagine, Spain and Italy are quite different from Norway, Sweden and Finland in numerous ways beyond just Vitamin D levels. For example, Spain and Italy never produced something like ABBA and the song “Dancing Queen.” Additionally, Italy and Spain faced the virus earlier than the Nordic countries and didn’t implement social distancing measures before the virus had a chance to spread widely. On top of all that, a study published in the journal Diabetes and Metabolic Syndrome found no correlation between Vitamin D levels and Covid-19 infection risk among 348,598 people in the U.K.

All told, right now, the grade for the amount of scientific evidence linking Vitamin D levels and Covid-19 risk would be not much better than a D. It hasn’t completely failed, but it’s not ready for a pass either. In theory, Vitamin D may be able to help reduce the possibility of or damage caused by a cytokine storm. But theory doesn’t always match reality, and more studies are needed.

So what should you do about the D during the pandemic? In some ways you can treat Vitamin D like toilet paper. Not literally, of course. Vitamin D supplements may help when the sun don’t shine, but ain’t supposed to go where the sun don’t shine. Instead, it’s all about determining what you really need while practicing moderation and not having unrealistic expectations. Neither toilet paper nor Vitamin D are the be all that ends all so to speak.

If you have low Vitamin D levels already, then getting more Vitamin D can be beneficial for things such as bone health anyways. So why not try increase your levels? Sunlight exposure and diet alone (e.g., eating oily fish such as salmon, egg yolks, fortified dairy products) may not provide enough of the D so taking Vitamin D supplements could help. Even when your levels are normal, a little extra Vitamin D likely won’t hurt. If you are an adult, the Recommended Dietary Allowance (RDA) of Vitamin D is 600 IU daily and 800 IU if you are older that 70 years of age, assuming that you don’t get an excessive amount of sunshine. What you want to avoid is overdoing it, taking over 4,000 IU in a day. Too much Vitamin D can bring problems, like too high calcium levels, gastrointestinal issues, bone loss, and even kidney failure.

Regardless, don’t rely on Vitamin D to protect you from the Covid-19 coronavirus. The jury’s still out on its effects. Moreover, even if it were to have some positive impact, Vitamin D certainly won’t do what social distancing, good hand hygiene, and properly disinfecting objects will do to prevent infection. It also wouldn’t do what a vaccine would be able to do. If you disregard social distancing and start mixing closely with others because you think Vitamin D is somehow protecting you, you would be making the wrong D-cision.

Source: Forbes