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It seems that with every passing day, opinions on how to best manage the current COVID-19 pandemic get louder, emotions get more passionate, and convictions get stronger. There’s no doubt that this historic time is affecting each of us in a unique, life-altering way. As the situation rages on and both health and economic implications mount, scientific data can help society more successfully navigate what to do next. 

One of these pieces of data is a recent research paper out Northwestern University, in which researchers analyzed data from 10 countries that have been hit hard by COVID-19 to explore the possible link between vitamin-D status and the outcomes among those who have been diagnosed.

Here’s a quick review of vitamin D’s role in health, along with a run-down on the takeaways from this study’s release about the potential links between the vitamin and coronavirus.

The Far-Reaching Effects of Vitamin D

Before diving into the specifics of the study, it’s important to note that the  health benefits of Vitamin D extend far beyond its potential role in infectious diseases and COVID-19 outcomes. Vitamin-D status not only influences just our immune response, but also supports blood-sugar regulation, heart health, bone health, mood, cognition, and more.

This is part of the reason we strongly recommend that each individual test their vitamin-D status regularly — twice per year, ideally — and work to optimize it. The Vitamin D Council recommends blood targets of 40 to 100 ng/mL (or 100 to 250 nmol/l) for most adults. 

If you have not had your vitamin-D levels tested recently, work with your healthcare provider to make it a priority. When you get tested, be sure to ask for 25(OH)D, or 25-hydroxy Vitamin D. 

More on the Recent Study 

Northwestern University researchers analyzed data from Germany, South Korea, China, Switzerland, Iran, France, Spain, Italy, the United Kingdom, and the United States.

Using curated data from each country, they determined the weighted averages of COVID-19 death rates for confirmed, hospitalized cases. They also factored in what is currently understood about the time it takes for this new coronavirus to progress from the time symptoms first start. 

From there, the team was able to draw parallels between lab markers that are known to be present in the advanced stages of severe COVID-19 infection, which can lead to fatal complications. They then cross-referenced those with known information about the population’s vitamin-D levels.

Additionally, they used calculations to attempt to splice out the impact of some other risk factors, such as age group. 

So, what did they conclude? 

Vitamin D deficiency may be a contributing factor to severe COVID-19. 

More specifically, they reported a 15.6 percent reduction in relative risk of death when compared with severe vitamin-D deficiency to normal vitamin-D levels.

Key Markers and What They Mean

The Immune System

There are two general aspects to our immune system: innate immunity and adaptive immunity

Innate immunity is like first-line defense and provides somewhat general protection — think mucous membranes in your nose, or changes in body acidity and temperature. Adaptive immunity is more specific to an infection: It responds when there’s a threat.

When the adaptive immune system becomes overactive and misfires, however, it can result in a life-threatening situation called “cytokine storm.” This is an extreme inflammatory state, when small proteins normally involved with the immune system are released too quickly and in amounts that can lead to severe respiratory distress and become fatal.

Researchers and health experts suspect that part of the reason the elderly population is being hit so hard with severe cases of COVID-19 could be due to a weakened innate immune system and over-activity of the adaptive immune system.

They also speculate that the opposite is true in children — a population that has not been affected as much — because they have not had a chance to develop a mature reaction to specific infections. 

C-Reactive Protein

A keystone of this study (outside of vitamin-D levels) is an inflammatory marker called C-reactive protein, or CRP, which is produced by the liver. When optimal, CRP levels should be less than 1 mg/L. When we experience infection, autoimmunity, stress, or trauma, CRP levels increase.

In their analysis, the research team reported that more than 80 percent of patients with severe COVID-19 infection progression had CRP levels over 10 mg/L. In other words, those in the direst circumstances from a COVID-19 infection had a nearly 10-fold increase in this inflammatory marker from what is considered ideal. 

These CRP levels were used as an indicator of the severity of the infection and suggestive of “cytokine storm.”

According to epidemiological studies, levels of CRP have been suggested to have an inverse relationship with vitamin-D status (meaning that when CRP is high, vitamin-D levels tend to be low, and vice versa). 

The Potential Role of Vitamin D with COVID-19 Progression

Vitamin D can support the first-line defense provided by the innate immune system. It’s also thought to have a role in moderating the adaptive immune system, helping to prevent it from spiraling out of control (such as the case of cytokine storm and related spikes of inflammatory CRP levels).

The study researchers found that those who had severe vitamin-D deficiency — defined as less than 10 ng/ML or 25 nmol/L — had a 1.4 times higher risk of higher C-reactive protein levels. They also identified that high CRP levels are tied to the severe inflammation found in the advanced, life-threatening stages of a COVID-19 infection.

The writers of the study summarize:

“Vitamin D may reduce COVID-19 fatality by suppressing cytokine storm.”

(Note: Vitamin-D deficiency in North America is rampant. Most people require supplementation to achieve the target levels for optimal health and functioning.)

Study Considerations

As we are bombarded with COVID-19 information, it’s important to have a solid understanding of what research releases mean — and what they don’t.

This particular study is an early release and has not yet been peer-reviewed. That means that other scientists have not been able to critique it for weaknesses and quality. (That step typically comes after a study, like this one, is pre-released, but before publication in a scientific journal.)

Additionally, this was also a population-based study, which does have limitations. The vitamin-D values used were based on previous population research and were not from the actual COVID-19 patients.

This means that associations between vitamin D, cytokine storm, and death of COVID-19 patients were drawn — the information is not of the caliber needed to draw any direct cause-and-effect conclusions quite yet. 

Key Takeaways

Despite any strengths or limitations of this particular study, the importance of vitamin-D status in overall health cannot be understated. Low vitamin-D status is tied to a myriad of health issues. And based on this research, one of those issues could be a severe progression of COVID-19 exposure into a life-threatening, inflammatory state. 

The good news, however, is that low vitamin-D levels are preventable.

We’re in a time where we can all benefit from more resilience and strength. From a physiological perspective, optimizing your vitamin-D levels to target ranges through a high-quality supplement is an easy win.

If you’re looking to supplement, we typically recommend 5,000 IU of a high-quality vitamin D3 (combined with vitamin K2) as a good place to start. However, knowing is always better than guessing, so be sure to get your levels tested and addressed regularly.

The healthiest, most optimal version of you depends on it.


Keep the conversation going.

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Samantha McKinney, RD, CPT

Samantha McKinney has been a dietitian, trainer and coach for over 10 years. At first, her interests and experience were in a highly clinical setting in the medical field, which ended up laying a strong foundation for understanding metabolism as her true passion evolved: wellness and prevention. She hasn’t looked back since and has had the honor of supporting Life Time’s members and nutrition programs in various roles since 2011.

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