Could vitamin D help with Covid?

As we’re heading into winter here in the Northern hemisphere, and if you’re spending rather more time inside your home at the moment, you’re probably not getting as much sunlight on your skin as in the summer months. And the body actually uses sunlight to make vitamin D, which is important for healthy teeth, bones and muscles. This week, a paper published in The Lancet: Diabetes and Endocrinology has looked at whether levels of vitamin D may be related to how someone might fare with Covid-19. And Chris Smith spoke to respiratory physician David Thickett, who wasn't involved in this study…

David - There are several strands of evidence that point to vitamin D protecting against viral respiratory infections. And there are similarities between the patterns of infection across the globe between the coronavirus seasonal influenza and the swine flu pandemic, whereby the greater the distance you move from the equator, the higher the case rates for those viral infections, which has implicated sunlight exposure, and potentially vitamin D deficiency is one of the possible causes of that.

Chris - What does it actually do to the immune system though? Because most people will be familiar with vitamin D in terms of its role in maintaining healthy bones and skeleton. So what's it got to do with immunity?

David - It's actually a very broad acting steroid hormone. It affects a very large number of cells outside of the bone, which is the classical actions of vitamin D, but it's certainly been implicated in immune health. Blood cells, such as lymphocytes respond to the vitamin D. And also other organs, such as the heart muscle strength, has been linked to having a good level of vitamin D. So it's a fairly protective hormone and very wide effect, which potentially have some advantages in the sort of severe lung injury that COVID pneumonia causes.

Chris - Presumably then someone has done the obvious experiment where they've measured vitamin D levels and then they've looked at people who have, or haven't had, severe infections with coronavirus and have tried to marry the two together?

David - Yeah. So we've done that pre-coronavirus. What Covid patients get is something called the acute respiratory distress syndrome, which is the very severe lung inflammatory response. And it can be due to pneumonia, viral pneumonia. You can get it after trauma or smoke inhalation, those sorts of things. And we'd shown that levels of vitamin D are very low in people who develop that syndrome. And gradually as the pandemic has gone on more and more papers have been published saying that this is possibly the same with coronavirus infections.

Chris - So, to answer my question then, is there data yet linking vitamin D levels when people are challenged with coronavirus and whether or not they do get severe Covid?

David - Yeah, basically the vitamin D deficiency is very common in Covid patients. And there are a number of papers that have come out recently that implicate it in the severity of the exaggerated immune response, but most of the studies are quite small. They have a limited number of controls, which there are some issues with because of the difficulties of doing this sort of research during a pandemic.

Chris - Obviously one other explanation is that it's just that other lifestyle factors that happen to be there alongside a low level of vitamin D are what's really causing the increased risk, and that the vitamin D is just an innocent bystander.

David - Yeah. So I mean, those studies are all observational. There are no large trials of treating Covid patients with vitamin D, but there is one trial called the Cordoba study and that study did show some positive responses to vitamin D treatment.

Chris - Are we in some respects treating the wrong people if we come in with vitamin D once a person is sufficiently unwell to have come to the notice of a doctor? Would it not be potentially more effective to give people supplementation with vitamin D before they even become infected with coronavirus? Because A that would help the fact that it looks like people who live in countries like ours across winter are chronically short of this important vitamin anyway, but also they would be therefore in better shape to cope with coronavirus if they caught it?

David - Well, I think there are two aspects - is vitamin D abuse as a preventative agent, and is it useful as a treatment once you've got Covid. In terms of prevention, there is evidence that it reduces viral respiratory tract infections. It's not huge, 12% reduction probably in the number of infections, but it may also impact the severity. So the government recommends 400 units a day during the winter, but that's probably an underestimate of what is needed. But there aren't any trials to show that giving vitamin D to prevent coronavirus, currently, where the results are available. Though one has been started in the UK very recently, it won't report 'til the spring at the earliest.

Chris - What are your instincts telling you? Do you think that we're going to end up in a position where it will turn out, actually, this is quite a useful intervention. And given that most of us are vitamin D deficient across winter in high latitudes, it wouldn't do any harm to advise people to just up their vitamin D intake anyway?

David - Yeah, I mean, I'm taking 4,000 units a day. Most of my consultant colleagues who work in intensive care in Birmingham are already taking vitamin D supplements. It's particularly important I think if you're of non-Caucasian ethnicity, those individuals are at much higher risk of vitamin D deficiency. So in targeted individuals, it could be extremely effective, I think, and you know, I'm taking it. And I recommend it to my patients when I find they're vitamin D deficient.