Does vitamin D protect you from COVID?
The story of vitamin D and its impact on our health is fascinating.
Low vitamin D levels are linked to basically every health malady you can think of - obesity, coronary artery disease, cancer, Alzheimer’s disease, Parkinson’s disease, congestive heart failure.
If you can think of a disease, I bet you that you can find a link between low vitamin D levels and that disorder.
Low levels of vitamin D have been linked with higher likelihood of getting COVID, more severe COVID infection, and worse COVID outcomes.
So it seems like a no-brainer that we should all be supplementing with vitamin D, right?
There’s a big buzz across many in the health and wellness world about the potential for vitamin D as an important part of COVID treatment:
So what are we waiting for?
If low vitamin D levels are linked to worse COVID outcomes, and supplementation is cheap and low risk, what’s the harm? Why aren’t we doing this for everyone? Why aren’t you taking vitamin D?
The story of vitamin D in treating disease
It’s a boring one.
If you talk to almost any doctor, they’re going to tell you that for all the impressive population based data showing that lower vitamin D levels are linked to worse health, the clinical trials looking at supplementation have always been underwhelming.
Any cardiologist or oncologist is going to tell you to look at the VITAL trial before you stock up on vitamin D supplements.
The VITAL trial is probably the biggest, best run, and most widely cited study looking at vitamin D supplementation.
This trial took about 26,000 men and women and supplemented them with vitamin D at 2000 IU per day, and followed them for almost 6 years to assess their risk of cancer and heart disease.
The study found no difference between the group that got vitamin D and the group that got placebo. Seriously, the groups are essentially identical:
So the reason that almost every doctor you ask about this is skeptical of vitamin D supplementation to prevent disease is because of huge, long-term studies like this one.
What about the COVID studies?
The trials that exist aren’t good enough to draw major conclusions about the role of vitamin D in COVID.
The biggest studies are just observational - they assess vitamin D status and severity of disease. These studies aren’t asking questions about treatment.
The randomized trials - the trials that actually test vitamin D supplementation versus placebo - aren’t impressive. Tiny numbers of patients, crappy surrogate endpoints, and minimal impact on any outcomes that matter.
Certainly nothing that’s a slam dunk to suggest that we’re missing a parachute effect.
So if the trials aren’t impressive, why are people doing worse when vitamin D levels are low?
This is the million dollar question about vitamin D and COVID (and heart disease, and cancer, and all the other diseases).
I can make an argument in each direction - that vitamin D supplementation is good and that vitamin D supplementation is pointless.
Let’s take each argument out for a test drive.
Argument 1: vitamin D supplementation is pointless
If supplementation with vitamin D actually did anything for disease, it would be apparent from the studies that have been done.
Plenty of medical treatments that seem like they make sense based on biology and epidemiology ultimately end up failing when they’re tested in a well run, randomized, placebo-controlled trial. Which means they don’t work (and it’s likely that unknown confounders explain the associations we’ve seen).
Ultimately, the biologic and epidemiological data lead us to create a narrative of why vitamin D works that can be very compelling.
If you’ve never heard of the Narrative Fallacy, click on that link and read about it. The narrative fallacy tells us that we overestimate our ability to understand cause and effect because we use the cognitive shortcut of creating a story for ourselves to simplify and understand the complicated facts of life.
Maybe vitamin D is similar. We invented this narrative of low vitamin D levels as a cause of poor health, but we misled ourselves.
The biology of vitamin D is complicated: while we make it from the sun and it’s found in certain components of our diet, you need a functioning liver and kidneys to convert it to its active form. So sicker people - those who eat a less healthful diet, those who spend less time outside, those with worse underlying health - will both get less vitamin D and convert less vitamin D to its active form.
Low vitamin D levels are really just a proxy for poor health.
Sicker people are sicker. When you’re sick, you will do worse no matter what disease we look at. So vitamin D supplementation doesn’t matter because it’s not solving the underlying problem.
And maybe that’s why the clinical trials haven’t shown a benefit: because it doesn’t work.
Argument 2: we should be supplementing with vitamin D
The argument for vitamin D doesn’t rely on cognitive biases or a complex biologic mechanism to make its case.
Let’s start with recognizing two important facts. First, vitamin D is easy because it’s cheap and readily available. Second, vitamin D supplementation is safe.
But we just went through all of the trials looking at how vitamin D supplementation doesn’t work. So we need to explain the weaknesses in those trials to make the case for vitamin D.
Every vitamin D study that I’ve ever seen suffers from the same flaw: they don’t actually test whether fixing a vitamin D deficiency improves health outcomes.
None of those studies - from VITAL to any of the COVID vitamin D trials - enrolled people who were found to have low vitamin D levels and provided them with supplementation to raise their vitamin D levels and then evaluated whether normalizing vitamin D levels improves disease outcomes. In other words, there’s never been a vitamin D trial that actually made sure that they were correcting a vitamin deficiency before looking at outcomes.
So none of these trials can answer the question that we’d hope they’re asking.
What’s the bottom line?
It’s hard to conclude that vitamin D is going to do anything but work on the margins based on the information that we have.
Vitamin D is not a miracle drug.
But it’s certainly reasonable to supplement with vitamin D if you’re deficient.
I have a hard time concluding that vitamin D supplements will do all that much for folks who have normal vitamin D levels.
But I also have a hard time arguing that it’s a mistake to use something cheap, safe, and easy to correct a known deficiency.
I doubt that it will make much difference in COVID, but I don’t see any signal for harm.
And I would always advocate for knowing your own blood levels of anything - from vitamin D to cholesterol to kidney function - before making any decisions about supplements or medications.
Thank you for reading! If you’re enjoying my newsletter, please consider sharing with your friends and family and encouraging them to subscribe!
I always appreciate any feedback or thoughts you might have. You can reply directly to this email to reach me directly.