Is vitamin D the answer to Covid?

Vitamin D has been a popular topic in the Covid-obsessed media lately, thanks to D’s role in immune function. Covid infections have been much more severe in countries where vitamin D levels are low. What are the possible explanations?

  1. Vitamin D can be made in skin that’s exposed to specific UV rays from sunshine. That specific UV wave length is absent in winter, particularly in northern regions, where Covid infections are indeed more widespread. And people who live inside get no sun exposure (nursing home residents, for example). No surprise then, hard hit areas tend to be farther north, particularly nursing home residents.
  2. Vitamin D production in skin is further impaired by darker toned skin. In the UK, health professionals have noticed that people from South Asian countries (Pakistan, India) have worse outcomes. In the US, African Americans have worse outcomes. Is vitamin D deficiency a contributing factor?
  3. Vitamin D is a fat soluble molecule. Obese people have lots of fat tissue, and vitamin D can get sucked into the fat cells, making it unavailable to the immune system. Obesity is a known risk factor for Covid severity; is it because fat tissue interferes with vitamin D activity?

They Saw The Light

You’d think people in Indonesia would have plenty of vitamin D in their blood. It’s a tropical country with intense sunshine all year long. But in fact, pale skin is prized in Indonesia, so people have traditionally shunned sun exposure. Many women wear the hijab, which effectively prevents all sun exposure. Until now. With all the hype about vitamin D and Covid, Indonesians are now deliberately sunbathing. One motivation is valid: the intense tropical sunshine stimulates vitamin D production in skin. One is false: sunshine kills the virus in a person’s body. Repeat: False. Intense sunlight can kill virus in the air or on surfaces, but not if it’s already inside your body. If you’ve been infected, your best defense is a healthy immune system.

One Piece of the Puzzle

Vitamin D is a critical part of general immune function. It also helps to control the cytokine storm caused by out-of-control inflammation. This hyper-inflammation leads to the devastating lung damage seen in Covid infections.

Is anyone collecting vitamin D lab data? Testing vitamin D in the blood of hospitalized patients? Testing vitamin D levels in people who have antibodies but had very mild infections? Testing vitamin D levels in nursing home residents? I’m not confident anyone has bothered to collect that data, which would be a terrible missed-opportunity to identify a potentially effective disease intervention.

Is vitamin D the answer?

Immune function depends on lots of other nutrients. They all work together. No one nutrient is the Be-All or End-All magical cure. So while the focus on vitamin D is encouraging, it’s not likely to be the sole answer. On the other hand, it’s not impossible. If all the pieces of the immune system are in place except one, and boosting the supply of that one makes all the difference, why wouldn’t you make that happen? It would be like driving your car with 3 good tires and one bald and slightly deflated tire. Your car isn’t going to move or handle very well in that situation.

Vitamin D sources


Getting vitamin D from food is problematic. Few foods have much. Certain canned fish (sardines, salmon, mackerel), and egg yolk have a small amount. Cod liver oil is a very good source, but is more of a supplement than a food. Some foods are fortified with some vitamin D: milk and ready-to-eat cereals are two common examples. Other foods, such as orange juice or energy bars, may be fortified with modest amounts.

In order to get sufficient vitamin D from food, you’d need to be a big milk drinker (6 cups/day) or a big fan of canned mackerel (9-10 oz every day). The most effective way to boost blood levels is with a supplement.


A blood test can show if your vitamin D level is deficient, which would suggest a supplement is a good idea. How much to take? Again that depends on you. If you have darker skin, are obese, rarely go out in the sun or live in a northern region, you might need more than someone who is fair skinned or who lives farther south.

A doctor who is knowledgeable about vitamin D supplementation for deficiency can suggest a suitable dose for you. One size does not fit all, and excessive intake can be a problem. Initially you might take a high dose to boost your levels, then cut back to a lower maintenance dose. Whatever the dose, take vitamin D with a meal that has some fat in it. Vitamin D is fat soluble, and needs fat to facilitate absorption. Taking it on an empty stomach or with a high carb beverage like juice or a soft drink is not helpful.

What if?

Research showing that vitamin D helps to lessen Covid infections would be tricky. You’d need to find a large number of people of varying ages and racial profiles, who had not been infected, measure their vitamin D and expose them to the virus. Then perhaps give deficient people vitamin D supplements. See if infections develop, and if so, if they become severe. Who would do this? No one.

So definitive clinical research is not going to happen. At best we can just make associations. Look at vitamin D levels of people with severe infections and compare to people who were infected but had only mild symptoms. This sort of backward-looking research could be done, but it wouldn’t tell us if vitamin D could actually prevent infection. So for now all we’ve got to go on is population data.

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