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This transcript has been edited for clarity.
welcome to Impact factor, Your weekly comments on new medical research. I am Dr. F. Perry Wilson of Yale University School of Medicine.
This week we’ll dive into the lion’s burrow again This study Appeared in PLOS medicineCould not show a causal relationship between. Vitamin D Level and COVID-19 incidence or severity.
And I know this is one of the hot button COVID problems. I think that’s because we all really want a cheap and easy way to avoid getting infected with COVID or getting serious COVID. And technically, it’s a vaccine, but certainly I wish we had more experience. I understand it.
And the observation data was definitely convincing.People with low vitamin D levels COVID results are really badIt’s much worse.
However, correlation is not causal. I’ve heard it, but I rarely elaborate on what that really means. Why is causality important? If A Cause If you change B, then A, B will change. When asked if vitamin D levels are low, Cause Even worse COVID, what we really want is whether we can protect ourselves from COVID by increasing the level of vitamin D.
If there is a causal relationship, the answer is yes. But it may not be. Many lower vitamin D levels and increase the risk of COVID. I often refer to vitamin D levels as lifestyle biomarkers. Higher in healthy and active people, and if infected with COVID, the very people you expect will be very successful.
The classic method of assessing medical causality is by randomized trials, and there are currently several trials of vitamin D supplementation with COVID. I created a simple table to emphasize what I know.
Here is a mixture of the results of a fairly small study that has already focused on sick people. The biggest research shows that there is no benefit. Small, poorly controlled studies show some benefit to soft results. No one has answered the question of whether providing vitamin D supplements to healthy people will later affect COVID.
So are we stuck?
It turns out that there is a smart way to evaluate causality that does not require randomized trials. It’s not perfect, but it may be the best we have. This is called Mendel randomization.
The mechanism is as follows.
I have a causal question: Is it low vitamin D level? Cause Bad COVID? However, vitamin D levels have been found to be affected by many lifestyle and environmental factors that we have no control over. But something else affects your vitamin D levels.
Some people are genetically prone to high vitamin D levels, just as they are genetically prone to be taller.Yeah, yours Actual Vitamin D levels are affected by everything else, but the genes are unchanged.
When low vitamin D is causally associated with worsening COVID, people with a genetic predisposition to low vitamin D have worse COVID than people with a genetic predisposition to high vitamin D. To be honest, it’s a pretty clever trick.
Of course, a large amount of data is needed to understand which genes (in this case, small fragments of genes called SNPs) lead to elevated vitamin D levels. Researchers in this study used approximately 450,000 people to create a genetic risk profile for low vitamin D levels. The scores were then used to assess the genomes of approximately 14,000 people infected with COVID and 1.3 million people not infected with COVID. If lower vitamin D levels are causally linked to worsening COVID, you would expect the COVID group to be rich in people with a low genetic predisposition to vitamin D.
However, this was not seen. Sensitivity to COVID, hospitalization for COVID, not a serious illness. This figure basically shows the following: I tried this in various ways, but no protection signal was displayed.
Butler Laporte, etc. PLOS medicine. 2021; 18: e100 3605. Source
At this time, vitamin D supplementation as a preventative strategy is largely unsupported.
However, there are some caveats. First of all, it is important to remember that this analysis is not limited to people with vitamin D deficiency. In reality, you need to supplement with a very small amount of vitamins. That’s why it’s a vitamin.
There are also more subtle issues in these Mendelian randomized studies of vitamin D. Do you know the genetic risk score they are calculating? It is based on the measured vitamin D levels. However, the vitamin D levels we measure in the blood are not the same as the bioavailable vitamin D.
We all have a protein called Vitamin D-Binding Protein. This protein binds to vitamin D in the blood, making it unavailable to cells. Some of us have a D-binding protein that has a high affinity for vitamin D. It is genetically determined.
In other words, two people with different personalities It was measured Vitamin D levels may have the same effective level of vitamin D, based on genetic variation of the D-binding protein. This means that the genetic risk score may not accurately capture what we are thinking, limiting the validity of this analysis. Of course, all observational studies that link lower vitamin D levels to worse results suffer from the same measurement problems.
Personally, I’m not a big fan of vitamin supplementation in general. I encourage my patients to get vitamins from their diet. For Vitamin D, get in the sun while exercising a little outdoors. Fortunately, summer is coming-going for summer.
F. Perry Wilson, MD, MSCE is an associate professor of medicine and director of clinical and translational research accelerators at Yale University. His science communication work can be found at the Huffington Post, NPR, here in Medscape.He murmured @fperrywilson Hosts a repository of his communication works www.methodsman.com..