Ever since the start of the pandemic, doctors have been looking for ways to improve survival of COVID-19 patients. They have explored several different treatments with varying results. Two studies published in 2021 examined the effects of vitamin D3, a compound known to have a powerful effect on the immune system. They came to vastly different conclusions. Studies suggest that vitamin D supplements don’t prevent infection with COVID-19. On the other hand, the most recent analysis indicates that people taking vitamin D are less likely to require intensive care.
How Do Vitamin D Supplements Affect COVID-19 Outcomes?
Could vitamin D supplements help protect people from the worst outcomes of COVID-19? Randomized controlled trials over the past few years have been inconclusive. (We have summarized a few of them below, so you can get an idea of the range of findings.)
Pooled Data Highlight ICU Benefit:
Scientists conducted an analysis on pooled data from five such studies (Pharmaceuticals, Jan. 16, 2023). As a result, the new analysis shows that people who took vitamin D supplements were less likely to need ICU care.
Researchers initially conducted these randomized controlled trials because vitamin D has anti-inflammatory activity. In addition, supplements appear to reduce the likelihood of other respiratory infections. By combining the data from the five scientific studies that met strict criteria, the researchers determined that vitamin D supplements reduced the chance of cytokine storm and the probability of a patient needing intensive care.
According to this analysis, the chance of death from COVID was cut nearly in half. However, the investigators say further studies are necessary to determine whether vitamin D was really responsible for improved survival of COVID-19 patients.
Vitamin D Supplements Don’t Prevent Infection:
Q. You’ve written about the possible benefits of vitamin D to boost immunity and protect people from infection. So perhaps you won’t like this at all. Here are studies showing that vitamin D does not help prevent COVID! What do you think?
A. Thank you for bringing this research to our attention. Both studies were recently published in The BMJ.
A British Study Finds No Benefit from Vitamin D Supplements:
One of the studies included 6,200 British adults who had not been taking vitamin D (BMJ, Sep. 7, 2022). The researchers tested blood levels of the study volunteers and assigned them on a random basis to get vitamin D supplements or not. If the scientists put subjects in the vitamin D group, they also prescribed either a high dose (3200 IU daily) or a low dose (800 IU per day) of vitamin D3. Only volunteers with blood levels below 75 nmol/L were offered supplements. Many experts consider 75 nmol/L an optimal blood level of 25-hydroxyvitamin D. During the six-month follow-up period, people taking vitamin D were no less likely to come down with a respiratory tract infection, including COVID-19.
Cod Liver Oil Did Not Make a Difference in Norway:
The other study was conducted in Norway (BMJ, Sept. 7, 2022). The scientists recruited more than 34,000 people who were not taking vitamin D supplements. Half of them were given cod liver oil and the other half placebo, taken daily during the winter. (On average, participants took the supplements for 164 days.) Cod liver oil contains vitamin D (10 mcg or 400 IU per daily dose). Unfortunately, participants taking cod liver oil were just as likely to contract COVID-19 or other respiratory infection as those taking placebo. Some vitamin enthusiasts will no doubt point out the 400 IU of vitamin D per day is a rather modest dose. While that is true, we would have expected a study of this size to show some results if the supplement were helpful.
In Spain, Vitamin D3 Improved Survival of COVID-19 Patients:
An earlier study had shown benefit from vitamin D supplements. Investigators at the Hospital del Mar in Barcelona, Spain, reported on 930 COVID patients admitted to their facility (Journal of Clinical Endocrinology and Metabolism, Sept. 27, 2021). Roughly half of these patients were assigned to vitamin D3. In contrast, the remainder did not get the supplement, although other aspects of treatment were similar.
The protocol was somewhat unusual. It called for 532 micrograms (21,280 IU) of calcifediol (oral 25-hydroxyvitamin D3) on the first day. Subsequently, patients took 266 mcg (10,640 IU) on days 3, 7, 15 and 30.
The results were striking when it comes to severe illness and survival of COVID-19 patients. About 5% of those getting vitamin D required intensive care, compared to 20% of those who did not. In addition, 6.5% of the vitamin D recipients died, in contrast to 15% of the control group.
The researchers conclude:
“In patients hospitalized with COVID-19, calcifediol treatment at the time of hospitalization significantly reduced ICU admission and mortality.”
Can We Trust These Results Regarding Survival of COVID-19 Patients?
The researchers initially posted the study before other scientists reviewed it. Some COVID researchers were skeptical. They suggested that the statistical analysis used might be incompatible with the randomization method. However, now that other scientists have reviewed it carefully for publication, it is reasonable to trust the results.
Epidemiologists in Catalunya and Barcelona conducted a different type of study to answer a similar question. In this population of more than 4 million, they compared adults taking vitamin D supplements to those not on supplementation (Journal of Endocrinological Investigation, Jan. 2022). Their results were far more modest, but still important. Among people whose 25-hydroxyvitamin D blood levels rose to at least 30 ng/ml (a level often used as a threshold for adequacy), supplements improved survival of COVID-19 patients. That was in comparison to people whose 25-hydroxyvitamin D levels showed deficiency and who did not take supplements.
High-Dose Vitamin D3 Did Not Shorten Hospital Stays in Brazil:
Further research will be essential. Researchers in Sao Paulo, Brazil, published their study of vitamin D3 for COVID-19 patients (JAMA, Feb. 17, 2021). This randomized clinical trial included 240 hospital patients with COVID-19. The scientists designed it to test the hypothesis that a single mega-dose (200,000 IU) of vitamin D3 would increase blood levels of 25-hydroxyvitamin D and shorten hospital stays.
The investigators were careful to use random computer generated codes to randomly assign half of the patients to take that big dose of vitamin D3 dissolved in peanut oil. The other half took peanut oil alone.
According to the investigators,
“The solutions were identical in color, taste, smell, consistency, and container.”
The study focused on length of hospital stay, but the researchers also collected information on survival of COVID-19 patients, admission to the ICU and need for ventilators. There were no significant differences between the groups on any of these measures. Even when the scientists took initial vitamin D deficiency status into account, they did not find meaningful differences. They concluded that their study does not support the use of vitamin D3 in treating moderate to severe COVID-19.
Mexican Pediatricians Find Vitamin D Supplements Improve Survival of COVID-19 Patients:
We haven’t yet heard the last word on this question. Mexican pediatricians published a small study in which their young patients were randomized to receive vitamin D supplements or not (Frontiers in Pediatrics, July 25, 2021). However, the investigators were aware of who was taking the supplements, so the research was not double-blind. Fewer of the children taking vitamin D required mechanical ventilation (10% vs. 36%). Even more important, just one child in the supplement group died (5%). In contrast, six (24%) of the patients in the control group died.
The scientists concluded:
“In this trial, VD supplementation in pediatric patients seems to decrease the risk of COVID-19 progression and death. More studies are needed to confirm these findings.”
If you are interested in utilizing vitamin D3 for more mundane purposes, you can learn a good bit about dosing, advantages and potential side effects from our eGuide to Vitamin D and Optimal Health. You might also want to listen to our interviews on this topic with Dr. David O. Meltzer of the University of Chicago and Dr. Bruce W. Hollis of the Medical University of South Carolina. It is Show 1240: The Link Between Vitamin D and COVID-19.