Vitamin D deficiency could increase susceptibility to severe COVID

Last updated on July 31st, 2022 at 02:02 pm

A new study seems to indicate that individuals with vitamin D deficiencies are more susceptible to severe COVID-19 outcomes. This does not mean that lots of vitamin D can prevent COVID-19 or prevent severe COVID in people with normal vitamin D levels, but it does indicate that this could be an easy way to reduce the risk of severe COVID-19.

I know I have a reputation of being “anti-supplement,” but I usually always write “supplements are useless unless there is a chronic medical condition that requires the supplement.” If you’re not getting any vitamin C in your diet, you can be at risk of scurvy, so taking vitamin C supplements is appropriate. If you are pregnant, folic acid supplements are important to reduce the risk of neural tube defects in your fetus.

The evidence for vitamin D and COVID-19 has been all over the place. Sometimes, I feel that vitamin D is the new great supplement to treat everything. I tend to be skeptical of supplements because they are overhyped. And too many people believe if a small amount does this, then a whole bunch of the supplement ought to boost your immune system or something. All it does is make us have very expensive urine.

Let’s take a look at this new paper. I think it sets out an evidence-based understanding of what vitamin D may do to reduce the risk of severe COVID-19 outcomes.

close up photo of sashimi vitamin D COVID
Photo by cottonbro on

What is vitamin D

Vitamin D is a group of fat-soluble secosteroids (it’s a scientific name for steroids with a “broken” ring). The most important chemicals in this group are vitamin D3 (known as cholecalciferol) and D2 (known as ergocalciferol).

Very few foods contain either of the important types of vitamin D. However, there are some foods that can be good sources for the vitamin:

  • Fatty fish, like tuna, mackerel, and salmon
  • Foods fortified with vitamin D, like some dairy products, orange juice, soy milk, and cereals
  • Beef liver
  • Cheese
  • Egg yolks

Many people with broad diets that include a lot of fish, eggs, and other foods can get sufficient vitamin D without supplementation. As I’ve repeated often, short of chronic malnutrition, we get plenty of vitamin D.

Moreover, vitamin D is produced by a process called dermal synthesis. That is, sunlight, specifically UV-B radiation, causes the synthesis of vitamin D in the skin. Technically, vitamin D isn’t a vitamin, because we can manufacture it, it is really a hormone. For this article, we’ll just call it a vitamin, even though scientifically it is not.

Although we can manufacture sufficient vitamin D by sunbathing every day, the body has a feedback loop that shuts down production to prevent toxicity. Yes, excess vitamin D is quite dangerous leading to many conditions such as over absorption of calcium to hypertension to fatigue. But it also can lead to some dangerous chronic conditions that we’ll discuss later.

Although humans can manufacture vitamin D by sitting in bright sun, there’s one major problem – the risk of skin cancer. As I’ve written before, there are very few ways to actually prevent cancer, but staying out of the sun is one of them.

Finally, the vitamin D we consume or produce in sunlight is not biologically active. It is generally activated by enzymatic conversion (in a process called hydroxylation) in the kidneys and liver into forms that the body can use — vitamins D3 and D2.

pile of various pills capsules in hands of anonymous doctor
Photo by Alena Shekhovtcova on

Vitamin D and severe COVID-19

In a new study, published on 3 February 2020 in PLOS ONE, Amiel A. Dror and colleagues examined blood vitamin D3 levels in patients hospitalized for COVID-19 at the Galilee Medical Center in Israel. The study was done during the first two coronavirus waves before vaccines were widely available. This study had concluded before the Omicron variant had become widespread.

The records of 253 individuals admitted between 7 April 2020 and 4 February 2021 to the Galilee Medical Center (GMC) in Nahariya, Israel, with positive polymerase chain reaction (PCR) tests for SARS-CoV-2 (COVID-19) were searched for historical vitamin D levels measured 14 to 730 days prior to the positive PCR test.

Here’s what they found:

  • Patients with a vitamin D deficiency were 14 times more likely to have a severe or critical case of COVID-19.
  • The mortality rate for those with insufficient vitamin D levels was 25.6%, compared with 2.3% among those with adequate vitamin D levels.

Amiel Dror, MD, the lead study author and a physician at the Galilee Medical Center, told The Times of Israel:

We found it remarkable, and striking, to see the difference in the chances of becoming a severe patient when you are lacking in vitamin D compared to when you’re not.

What we’re seeing when vitamin D helps people with COVID infections is a result of its effectiveness in bolstering the immune systems to deal with viral pathogens that attack the respiratory system. This is equally relevant for Omicron as it was for previous variants.

The study authors concluded:

From the early stages of the COVID-19 pandemic, establishing vitamin D deficiency as a risk factor was the aim of many investigators. It was subject to much debate in the general public and multiple medical journals. Our study contributes to a continually evolving body of evidence that suggests a patient’s history of vitamin D deficiency is a predictive risk factor associated with poorer COVID-19 clinical disease course and mortality. The use of historical results obtained before the COVID-19 pandemic as part of a public health survey enabled us to suggest vitamin D deficiency contributes to the causal pathway of COVID-19 mortality risk and disease severity. Our study warrants further studies investigating if and when vitamin D supplementation among vitamin D deficient individuals in the community impacts the outcome of an eventual COVID-19 episode.

What does this mean

I want to first stress with all of the power that I can muster that vitamin supplements aren’t a substitute for vaccines but they can help individuals with suboptimal blood vitamin D levels.

What this study doesn’t establish:

  1. That vitamin D is a cure for COVID-19.
  2. That taking more vitamin D, if your blood levels are normal, has any effect on the disease.
  3. That vitamin D “boosts” the immune system.
  4. Whether vitamin D is a causal factor for improved COVID-19 outcomes.
  5. Potential mechanisms as to why vitamin D may be correlated with severe COVID-19.

I worry that people think that this type of study means we should all go buy a bottle of vitamin D supplements and take a handful. However, if you get a blood vitamin D diagnostic test, and it shows that your levels are low, your physician can recommend the proper amount to take daily or weekly to maintain a healthy level of vitamin D. Doing that may help you during this ongoing pandemic.

One more thing. There are some curious data issues that probably aren’t germane to the quality of the study, but it’s bothersome. They split the population between Arab and non-Arab. The total number of those individuals does not equal the number of patients in the various COVID-19 severity groups. It’s an annoying error that should be corrected, but unless they made this all up, it shouldn’t have an impact on the quality of this article.

One last thing. I do not think there is a scientific consensus about vitamin D and COVID-19. There are still studies that don’t support this association, so I remain unconvinced that vitamin D does anything here. However, this study is sufficiently strong enough that it couldn’t hurt to take vitamin D, as long as it’s to fix a deficiency.


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