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Vitamin D and COVID-19

Dr Karen Martin
Reviewed by Dr Karen MartinReviewed on 19.10.2023 | 4 minutes read

Vitamin D has been hailed as an aide in the fight against COVID-19. Judging by the empty supermarket shelves, the public is listening. But what’s the theory behind it, and where’s the evidence? Can vitamin D stop us from catching COVID-19? Or stop it from making us very ill? We’ve examined the facts.

Why do scientists think vitamin D fights COVID-19?

Vitamin D strengthens bones and teeth, relieves muscle aches, keeps blood vessels elastic, and wards off depression and mental fatigue.

Some think it may also play a role in the immune response to fight off respiratory infections. Coronavirus is one such infection – a particular strain is a virus causing COVID-19 disease.

Vitamin D deficiency is more common in the Black, Asian, and minority ethnic (BAME) community, elderly and nursing home residents, and those with long-term health conditions such as obesity, diabetes, and high blood pressure. These groups are also the people most susceptible to the COVID-19 virus and the most at risk of serious illness and death.

Where's the evidence?

We can look at this from how people fared if they were vitamin D deficient and caught COVID-19.

A combined review of research papers (a systematic review) found low vitamin D levels in all patients with COVID-19, out of nearly 5,000 people. These patients were more likely to have high blood pressure, cardiovascular disease, chronic kidney disease, diabetes, obesity, and respiratory conditions, like asthma and COPD. So should we conclude that vitamin D deficiency puts those already vulnerable because of their health conditions at even higher risk? Or are these not linked, and those with vitamin D deficiency are more likely to be unwell from COVID-19?

Another systematic review found that two out of three had vitamin D deficiency in those with the most severe COVID-19 illness. Those who were deficient were more likely to be admitted to the hospital or to die. One conclusion is that vitamin D could protect against more severe diseases.

However, a study in Spain found no link between vitamin D deficiency and the severity of the disease. They did agree that most patients admitted to the hospital with COVID-19 had low vitamin D levels.

So what do we make of the conflicting evidence? It is a possibility that vitamin D deficiency may allow COVID-19 infections in and may make any COVID-19 infection much more severe. However, many factors are at play, and these groups are at risk of many health complications, so this needs more research before scientists declare there is a definite link.

What if we start taking vitamin D when we get COVID-19?

This is another way scientists have looked for evidence of a relationship between vitamin D and COVID-19: if you catch COVID-19, will starting vitamin D medication help you on to recovery?

One study from India found that those with a positive COVID test but mild disease or without symptoms had swabs that turned negative more quickly. Other markers of immune system activity are reduced more rapidly with high-dose vitamin D supplements.

Another study from Brazil found that high doses of vitamin D did not help severely ill COVID-19 patients, did not prevent the need for ventilators, or increased the chance of survival.

King’s College London researchers found that vitamin D supplements may reduce the chance of catching COVID-19 by 9%, but this was only true for women. However, protection from COVID-19 was higher for those taking probiotics (14% reduction), multivitamins (13%), or omega 3 (12%). But, could these people be more health-minded, adhering to all the safety measures when out and about to reduce risks, and perhaps less likely to suffer lifestyle-related conditions such as diabetes?

Vitamin D supplements don’t usually cause side effects or problems. If you’re taking a standard dose regularly (10 micrograms or 400 international units), there is no risk of toxicity unless you have certain medical conditions such as cancer or severe kidney disease.

There is no strong scientific evidence to show that a very high intake (i.e., mega supplements) of vitamin D will be beneficial in preventing or treating COVID-19.

So the verdict is…

Well, it’s tricky. Some studies have seen a positive gain, but other studies have shown vitamin D levels have little or no effect on COVID-19. It’s also a complex picture in this brand new disease, raising questions about whether those with COVID-19 in the community can be compared to those in the hospital and how we can account for age, gender, weight, and other health problems to give a one-size-fits-all verdict.

We await more research. But in the meantime, it has been recognized that vitamin D deficiency may be a bigger problem than ever, as the pandemic has kept many indoors.

With the relatively low risk of taking supplements and all of the health benefits of keeping vitamin D levels topped up, it may make sense to take them, particularly from October to April. Those at higher risk of deficiency should take supplements all year round.

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This article has been written by UK-based doctors and pharmacists, so some advice may not apply to US users and some suggested treatments may not be available. For more information, please see our T&Cs.
Dr Karen Martin
Reviewed by Dr Karen Martin
Reviewed on 19.10.2023
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