Hi, Everyone,

A group of researchers in the U.S. just published a study that adds to the now overwhelming body of evidence linking vitamin D to COVID-19. 

This study, which examined the records of 287 patients hospitalized for COVID-19 at Boston University Medical Center from March through August of 2020, was observational in nature, so it cannot prove a causal relationship. 

However, it had two strengths relative to many previous vitamin D studies:

  1. The researchers only included patients who had a 25D level measured within a year prior to admission. This reduces the likelihood of reverse causality (i.e., that patients with COVID-19 have low 25D levels because the disease suppresses vitamin D). It also addresses the problem we’ve seen with some studies that used 25D measurements from 10+ years prior to hospital admission. 
  2. The researchers defined vitamin D sufficiency as >30 ng/mL. Many previous studies have used a cutoff of 20 ng/mL or even 10 ng/mL, which many institutions, including the U.S. National Institutes of Health and the Endocrine Society, would define as deficient. 

The findings of this study were remarkable.

After adjustment for confounding factors, patients >65 years old (i.e., those at greatest risk) with 25D levels >30 ng/mL experienced a:

  • 67 percent reduction in mortality
  • 78 percent reduction in acute respiratory distress syndrome (the primary cause of death from COVID-19)
  • 74 percent reduction in severe sepsis

Perhaps most impressively, across all patients with a body mass index (BMI) <30, 25D sufficiency was associated with an 82 percent reduction in mortality!

This is phenomenal news, right? 

So, where are the news headlines discussing the results of this study and tying them to the many previous observational and experimental studies with similar findings?

Where is the public health advice encouraging people to maintain adequate vitamin D levels as a means of protecting them against serious COVID-19 outcomes (and perhaps against infection in the first place)? 

Where, indeed? 

Virtually all of the news we see on COVID-19 prevention and mitigation is on vaccines, masks, and social distancing—including heated debates about the relative contribution of each of these interventions. 

I’m not saying these interventions aren’t important. I think the impact of the vaccines has already been enormous and will continue to grow as more people get vaccinated. But there are still many unanswered questions about the vaccines, including how long the immunity they confer will last and how effective they will be in the face of new variants. 

Vitamin D is cheap, accessible, affordable, and safe. It has many benefits above and beyond protecting against COVID-19. And the protection it offers would be expected with all variants of the virus (and other viruses) because it supports our innate immune response, not targeting anything in particular. 

There is no downside whatsoever to advising people to maintain normal vitamin D levels and giving them guidance on how to do that during this pandemic—only upside. Yet, we are still not seeing this in the U.S. and most other countries. This is inexcusable. 

I need to mention one more important thing about this study. 

In obese patients (BMI >30) under 65 years old, the association between serum 25D levels and mortality disappeared. Put another way, obesity seemed to eliminate the protective effect of having normal vitamin D levels in this age group

Why would this happen? 

One possible explanation is that obesity decreases the conversion of 25D, the less active form of vitamin D, to 1,25D, the more active form. Prior research has suggested people who are obese may need higher amounts of vitamin D (whether through sun exposure, food, or supplements) and perhaps higher serum levels of 25D to maintain sufficient biological vitamin D activity.

This may be another reason why obesity significantly increases the risk of hospitalization and death from COVID-19. And it could give clinicians an important tool—treatment with vitamin D—for reducing the excess risk in obese people. 

But that will happen only if prevention and treatment with vitamin D becomes part of the routine advice, which hasn’t happened yet. 

In health,


P.S. This Saturday, March 20, I’ll be presenting in depth on this topic of vitamin D and COVID-19 at the IHH-UCSF Symposium on Nutrition and Functional Medicine. I’ve spoken at this conference for several years, and it’s a fantastic event. This year, it’s 100 percent virtual, so you can attend from anywhere in the world. Click here to learn more and purchase a ticket, and use the code “CHRISKRESSER” to get a 10 percent discount.