When the pandemic struck, many Americans turned to vitamins and supplements in hopes of boosting their immune systems.
Scientists also rushed to study them. Vitamin D, perhaps more than any other, has attracted the attention of researchers.
Even the country’s leading infectious disease physician, Anthony Fauci, accepted the idea of using the vitamin to keep COVID-19 afloat, and said in September that he was taking a supplement to prevent it from failing. that he “does not mind recommending it.
So should you take vitamin D to prevent or even treat COVID-19?
More than a year into the pandemic, many of the studies that can provide high-quality evidence are still ongoing, but there is now enough to provide clues – as well as feed for lively debate – on the question.
But first – why vitamin D?
It is unrealistic to think that any supplement can be a drug, but there are compelling reasons to study vitamin D in the context of COVID-19.
Vitamin D plays an important role in bone health and, along with calcium, helps people develop osteoporosis. And there is growing evidence that it helps the immune system to function properly.
In recent years, researchers have increasingly studied the effect of vitamin D supplementation on respiratory infections. Some clinical trials have found no significant effect, and others suggest that it may be protective.
A 2017 study in which 25 randomized, controlled trials were analyzed concluded that vitamin D could prevent acute respiratory infections.
Vitamin D can help strengthen the innate immune system in several ways, said Dr. Adit Ginde, a professor of emergency medicine at the University of Colorado School of Medicine and one of the authors of the study, said. One mechanism, he said, is by increasing antimicrobial peptides, which act as natural antibiotics and antiviral protectors against pathogens.
Although some researchers are not yet convinced of the evidence for vitamin D and respiratory diseases, others, such as Ginde. “Based on those mechanisms, prevention [of COVID-19] would be the first scenario you would expect to work, “Ginde said. It is also very clear that deficiencies cause the dysfunction in the immune system. “
The link to COVID-19
It is estimated that as many as 40% of the US population does not consume enough vitamin D and that as many as 1 billion people worldwide are deficient.
Early in the pandemic, researchers noted that the overlap between populations at high risk for serious diseases due to COVID-19 and those likely to be vitamin D deficient, especially overweight people, the elderly and those with dark skin.
This has given rise to comments and academic articles on whether raising vitamin D levels can protect certain vulnerable people from coronavirus infections.
There are now quite a few observational studies and a large review of the available evidence showing that low vitamin D levels are associated with higher risks of contracting COVID-19 or becoming seriously ill.
“What is clear from a number of studies is that there is a strong link with regard to your levels before infection,” said Dr. Shad Marvasti, a professor of family and preventative medicine at the University of Arizona College of Medicine in Phoenix, said.
Marvasti said the low levels of vitamin D were linked to an increase in cytokines – a cell-to-cell chemical messenger responsible for inflammation.
A study of 489 patients was published in JAMA Network open in September found ‘the relative risk of testing positive for COVID-19 was 1.77 times greater’ for patients who were likely to have vitamin D deficiency compared with those with adequate levels.
“It was really very striking,” says Dr. David Meltzer at the University of Chicago, who was the lead author of the study. “I started taking it and telling all my family and friends.”
In another recent study, Meltzer also found that black people with a high level of vitamin D were less likely to test positive than those who had levels traditionally considered adequate.
In another small study among patients hospitalized in COVID-19 in Spain, it was found that more than 80% have vitamin D deficiency, compared to 47% of the general population. however, there is no link between vitamin D levels and the severity of the disease.
“If I had money on it, I would bet it’s more likely that vitamin D is useful than not in COVID, but I’m not sure,” Meltzer said.
No “firm conclusions”
While these studies have raised hopes among some researchers, others are skeptical and note that most of these are observational studies, not the randomized, controlled trials standardized according to gold.
Much of the available evidence shows only connection – not causality – and even the results are mixed, said Walter Willett, a professor of nutrition and epidemiology at the Harvard TH Chan School of Public Health.
“It would be one thing if we had very consistent evidence, but it shows some benefit or no benefit,” Willett said. “At this point, we can’t really draw firm conclusions.”
Indeed, some observational studies have found no significant associations when it comes to key questions around COVID-19 and vitamin D levels.
Researchers in Greece recently concluded that vitamin D deficiency “is not significantly related to COVID-19 infections, recovery or mortality among European countries.” And in December, a British National Health Service agency reviewed the evidence and advised the public not to take vitamin D to prevent or treat COVID-19.
“We did not completely rule out vitamin D, but I am skeptical because I have worked in this field for 15 years, “said Dr. Erin Michos at the Johns Hopkins School of Medicine, who studied the effect of vitamin D on heart attacks. strokes and other cardiovascular diseases.
Researchers have for many years found the link between low vitamin D and other diseases – obesity, diabetes, cardiovascular disease, depression, multiple sclerosis and cancer – but either achieved conflicting results or found no clear benefit from supplementation.
People with low vitamin D levels tend to be less healthy in general: they spend less time outdoors and have less exposure to sunlight, and overweight people often have lower levels because fat cells sequester vitamin D.
“Vitamin D deficiency is therefore related to things like older age, obesity and a minority ethnicity,” Michos said. “Yet these are the same risk factors associated with severe COVID.”
This overlap makes it difficult to study the impact of vitamin D on COVID-19, as it is difficult to tell whether low levels are actually more susceptible.
“It can only be an indication of poor health and not really something that can be done to prevent COVID,” Michos said.
What about the treatment of COVID-19?
Research on the use of vitamin D as a therapeutic intervention once people have been infected with the coronavirus has yielded higher quality data, although the studies present a conflicting picture.
The most substantive evidence comes from a randomized, placebo-controlled trial in Brazil. There, doctors gave COVID-19 patients in the hospital one large dose of vitamin D and concluded that it ‘did not significantly’ reduce the patients’ stay in the hospital compared to the placebo group.
There are a few caveats: patients only received vitamin D later in the disease, and it was a single large dose, rather than more incremental, regular doses, which seems to ‘work better to protect immune function’, the Meltzer of the University of Chicago. said.
While the 240-person study could easily have missed ‘clinically important benefits’, the results are not encouraging, says Ginde of the University of Colorado, who wrote an editorial on vitamin D and COVID-19 for JAMA.
“If it was a miracle cure, you would see it,” he said.
What should you do then?
So far, there is simply not enough evidence to recommend taking a certain dose of vitamin D to combat COVID-19, but experts stress that it is reasonable to note whether people are getting enough, especially during the winter months. when the levels tend to drop. .
“There are many good reasons to avoid low vitamin D levels. “A supplement is really the most reliable way to get it,” said Willett of Harvard.
But as with many vitamins, Willett emphasizes that “more is not better.”
Because vitamin D is fat-soluble (as opposed to vitamin C, which is water-soluble), there is a risk that excess supplementation can lead to toxicity. Some research shows that ingesting more than 50,000 IU, or international units, is regularly harmful.
According to the Endocrine Society, there are different guidelines for how much vitamin D adults should get daily, ranging from about 400 to 1,000 international units.
Marvasti said most people ‘can probably get away with about 1,000 IU a day’, although it’s best to check your baseline levels first and talk to a doctor.
“Given the role that vitamin D is known to play in immunity and other medical conditions, what is my harm?”
Some clinicians are more careful.
“I do not recommend patients take it to prevent COVID-19,” Michos told Johns Hopkins.
Apart from the debate over vitamin D, Michos points out that there are many time-tested ways to boost the immune system – to eat vitamin-rich foods such as fruits and vegetables, exercise regularly, drink moderately and more importantly, get enough sleep. .
“I don’t think patients necessarily have to waste their money on supplements,” she said.
But Meltzer, who is more hopeful about the potential benefits of vitamin D intake, points out that there are still major gaps in understanding what a ‘normal’ level is, ‘because it’s largely defined on the health of the leg. ‘
“We do not really know what the ideal levels for immune function are,” he said. “Depending on your skin color and racial background or genetic background, there are many, many different needs, so this is an area that urgently needs more data.”
