The internet was flooded recently with reports that vitamin D for coronavirus may be either a treatment or prevention. Or it may reduce the severity of COVID-19.
But what does the real data say? Does it say that there is a solid benefit of vitamin D for coronavirus? Is there strong evidence that it can help prevent or treat COVID-19?
The answer is complicated. This is why I am annoyed by science journalists – they don’t critically analyze the underlying science published in peer-reviewed journals. It’s almost like the whole hydroxychloroquine fiasco – latch onto weak evidence and make outlandish claims.
So let’s look at a few recent studies about vitamin D for coronavirus.
What is vitamin D
Vitamin D is a group of fat-soluble secosteroids (it’s a scientific name for steroids with a “broken” ring). The most important chemicals in this group are vitamin D3 (known as cholecalciferol) and D2 (known as ergocalciferol).
Very few foods contain either of the important types of vitamin D. However, there are some foods that can be good sources for the vitamin:
- Fatty fish, like tuna, mackerel, and salmon
- Foods fortified with vitamin D, like some dairy products, orange juice, soy milk, and cereals
- Beef liver
- Egg yolks
Many people with broad diets that include a lot of fish, eggs, and other foods can get sufficient vitamin D without supplementation. As I’ve repeated often, short of chronic malnutrition, we get plenty of vitamin D.
Moreover, vitamin D is produced by a process called dermal synthesis. That is, sunlight, specifically UV-B radiation, causes the synthesis of vitamin D in the skin. Technically, vitamin D isn’t a vitamin, because we can manufacture it, it is really a hormone. For this article, we’ll just call it a vitamin, even though scientifically it is not.
Although we can manufacture sufficient vitamin D by sunbathing every day, the body has a feedback loop that shuts down production to prevent toxicity. Yes, excess vitamin D is quite dangerous leading to many conditions such as over absorption of calcium to hypertension to fatigue. But it also can lead to some dangerous chronic conditions that we’ll discuss later.
Although humans can manufacture vitamin D by sitting in bright sun, there’s one major problem – the risk of skin cancer. As I’ve written before, there are very few ways to actually prevent cancer, but staying out of the sun is one of them.
Finally, vitamin D we consume or produce in sunlight is not biologically active. It is generally activated by enzymatic conversion (in a process called hydroxylation) in the kidneys and liver so that the body can use it.
Despite the wild claims about the value of vitamin D in disease prevention, there is precious little evidence that it has much value.
Studies have provided observational data that compared outcomes from a few countries that suggest an inverse link between vitamin D levels and the severity of COVID-19 outcomes, including mortality. Although these studies did not examine the actual effect of vitamin D on the immune response to coronavirus, the researchers did make suggestions of a possible mechanism.
In a study published in the Irish Medical Journal, researchers noted that Spain and Northern Italy had high rates of vitamin D deficiency and have experienced some of the highest COVID-19 infection and mortality rates in the world. Moreover, those countries do not regularly fortify foods with vitamin D nor do they recommend supplementation.
On the other hand, people in northern European countries like Norway, Finland, and Sweden have higher levels of vitamin D, despite less exposure to sunlight, because of supplementation and fortification of foods. These Nordic countries had concomitantly lower rates of coronavirus infection and mortality.
The researchers reported that the correlation between low blood vitamin D levels and COVID-19 mortality was statistically significant. The authors concluded that:
Optimising vitamin D status to recommendations by national and international public health agencies will certainly have benefits for bone health and potential benefits for Covid-19. There is a strong plausible biological hypothesis and evolving epidemiological data supporting a role for vitamin D in Covid-19.
For example, the average Italian consumes 1493 cigarettes per year and the average Spaniard smokes 1499 per year. Alternatively, the average Swede only consumes 716 while the average Norwegian smokes 553. If I were looking at the data I’d say, “aha, it’s all about smoking and coronavirus.” I actually might be right, since smoking is destructive to the lungs making it easier for COVID-19 to infect a person.
There could be so many differences between these populations from diet to obesity to something that we haven’t even considered previously.
Clifford Rosen, MD, senior scientist at Maine Medical Center’s Research Institute in Scarborough, has been researching vitamin D for 25 years recently stated that:
There’s no randomized controlled trial for sure, and that’s the gold standard and the observational data are so confounded, it’s difficult to know.
As I’ve written before, we can only accept that there is a causal link with vitamin D for coronavirus treatment or prevention if we can establish a biologically plausible mechanism. Is there a way that vitamin D can have a beneficial effect on the immune system?
The immune system is incredibly complex – it contains a nearly infinite number of interconnections between organs, cells, and millions of biomolecules. Attempting to use any substance to “boost” the immune system is nearly always a myth. It’s pure pseudoscience.
In fact, the immune system works quite well except in cases of chronic diseases or chronic malnutrition. Even if you could boost your healthy immune system, that’s actually bad – allergies and autoimmune diseases usually result from an overactive immune system.
One hypothesis for the role of vitamin D for coronavirus treatment is that vitamin D may “blunt” the immune system’s response to the virus. For example, some researchers have surmised that the virus causes a cytokine storm, which is a systemic inflammatory response to certain infections.
Essentially, white blood cells release inflammatory cytokines that activate more white blood cells which then release more of these inflammatory cytokines. It gets out of control and can lead to death. Cytokine storms are hypothesized to have been one of the causes of the high mortality rate from the 1918 flu pandemic.
Researchers are proposing that low vitamin D levels somehow allow the cytokine storm to occur in some people. However, they’re not claiming that more vitamin D is going to make it better, they’re just saying that we should supplement if we have a compromised vitamin D level.
In a study that is available as a preprint (meaning it hasn’t been peer-reviewed), researchers examined hospital data from China, France, Germany, Italy, Iran, South Korea, Spain, Switzerland, United Kingdom, and the United States.
They showed that the risk of “severe” COVID-19 cases was about 15.6% higher in patients with severe vitamin D deficiency compared to patients with normal vitamin D levels.
The authors stated that:
This potential effect may be attributed to Vitamin D’s ability to suppress the adaptive immune system, regulating cytokine levels and thereby reducing the risk of developing severe COVID-19.
There are also large studies that have shown no evidence that vitamin D for coronavirus is useful. The authors examined nearly 350,000 patients in the UK’s Biobank, which stores patient blood and tissue samples for future research. The authors determined vitamin D levels in patients with and without a COVID-19 infection.
They found that:
Our findings do not support a potential link between vitamin D concentrations and risk of COVID-19 infection, nor that vitamin D concentration may explain ethnic differences in COVID-19 infection.
In other words, in a well-controlled study, the researchers not only did not find a link between vitamin D and coronavirus, but they also didn’t show a link that might have explained ethnic differences.
What can we conclude?
To me, the data is all over the place. This is a perfect example of the need for a systematic review that can clean up the data and see if there is unbiased and statistically significant data supporting the use of vitamin D for coronavirus treatment or prevention.
At this point, we would really need a well-designed, large, randomized, double-blinded clinical trial to see if there is a difference in outcomes from a COVID-19 infection between normal and low vitamin D levels in patients. That’s going to take time.
I suppose that since there is some intriguing evidence that vitamin D may have some effect on coronavirus infection outcomes, one could easily get a blood level diagnostic test (yes, it requires a needle removing some blood). Changing levels of vitamin D is fairly straightforward – a systematic review concluded that “single vitamin D3 doses ≥300,000 IU are most effective at improving vitamin D status…for up to 3 months.”
No researcher is suggesting that taking excess vitamin D will have more of an effect. This is one of the odd claims of supplement pushers who think if getting a normal level of vitamin D is good, pushing it higher is better. As I mentioned above, more vitamin D isn’t necessarily a good thing for the body.
I know that the alternative medicine crowd is pushing vitamin D for coronavirus. The evidence that it does anything is quite weak, and, typical for those who push pseudoscience, they cherry-pick research that supports their claims and ignore the research that doesn’t.
- Hastie CE, Mackay DF, Ho F, Celis-Morales CA, Katikireddi SV, Niedzwiedz CL, Jani BD, Welsh P, Mair FS, Gray SR, O’Donnell CA, Gill JM, Sattar N, Pell JP. Vitamin D concentrations and COVID-19 infection in UK Biobank. Diabetes Metab Syndr. 2020 May 7;14(4):561-565. doi: 10.1016/j.dsx.2020.04.050. [Epub ahead of print] PubMed PMID: 32413819; PubMed Central PMCID: PMC7204679.
- Kearns MD, Alvarez JA, Tangpricha V. Large, single-dose, oral vitamin D supplementation in adult populations: a systematic review. Endocr Pract. 2014 Apr;20(4):341-51. doi: 10.4158/EP13265.RA. Review. PubMed PMID: 24246341; PubMed Central PMCID: PMC4128480.
- Laird E, Rhodes J, Kenny RA. Vitamin D and Inflammation: Potential Implications for Severity of Covid-19. Ir Med J; Vol 113; No. 5; P81.
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