Summer sun, vitamin D and coronavirus: this is what we know

Ever since the coronavirus started to spread, the question has been asked again and again: is it a seasonal virus, which strikes mainly during and after winter? Not for the time being, virologists say – the inhibitory effects of higher temperatures and humidity are too weak. But immunologists add another seasonal factor: sun exposure. Some new studies often find low vitamin D levels in seriously ill corona patients. No causal relationship has yet been established.


The sun is our main source of vitamin D. The daily requirement can be reached after just a few minutes of sunbathing. But then you must be outside enough on an annual basis, with bare skin, and the sun must also be sufficiently high.

Therefore, people in the Northern Hemisphere have the lowest blood levels of Vitamin D in early spring, and they are often much higher at the end of the summer. Do varying vitamin D levels affect our susceptibility to the coronavirus? Researchers are usually cautious. There is no vitamin or mineral that does not play a role in the human immune system.

A healthy lifestyle and nutrition provide what you need; adding extra vitamins therefore gives little added value and can even be harmful, is often the warning.

‘Whole tribes are deficient in vitamin D’

This is slightly different for vitamin D, says Willem Koert. “Entire tribes are deficient in vitamin D. We just do not get out enough to make enough of it. According to the Nutrition Centre, many people should use vitamin D supplements to make up for that deficiency.”

Koert is a specialized medical science journalist who closely follows the research into the coronavirus. These studies are now being published in such a hurry that they have often not yet been tested by colleagues. And so, journalists should also be extra careful when writing about it.

Climatically you will encounter crazy patterns, such as a lower vitamin D value in Italy than in people in Sweden and Finland. That’s because diet and supplementation also play a role.”
Vadim Backman, researcher

But the publications are now starting to pile up nicely, says Koert. He refers to older studies showing that vitamin D supplements reduce the risk of flu and colds. And several recent studies find strikingly strong links between vitamin D and the severity of the disease course of COVID-19 – the disease caused by the coronavirus.

Often low vitamin D value in seriously ill corona patients

The latest publication comes from an American research group at North-western University. They compared patient data from hospitals in Asia, Europe and the US and concluded that patients in countries with relatively high mortality, such as Italy, Spain and the United Kingdom, had significantly lower vitamin D blood values than patients in countries where mortality is lower. Vitamin D is said to maintain the immune system while slowing down a dangerous overreaction – the dreaded cytokine storm.

“Sun exposure is an important factor for vitamin D,” lead researcher Vadim Backman tells “At the end of winter, vitamin D is much lower than in summer. But climatically, you will come across crazy patterns, such as a lower vitamin D value in Italy than in people in Sweden and Finland. This is because diet and supplementation also play a role – as do cultural factors such as whether people sunbathe. ”

Low vitamin D status has been more often associated with more serious respiratory infections, including flu viruses.”
Immunologist Carla Peeters

Dietary factors include the consumption of fatty fish, which also contains vitamin D, or green vegetables. The latter contains vitamin K, which according to Backman enhances the effectiveness of vitamin D.

Previous studies in Asia have already found that corona patients with relatively minor complaints often had significantly higher vitamin D levels than people who became seriously ill. The difference in risk would be almost tenfold. But then you keep the chance of sham connections – a low vitamin D level can also indicate the presence of other diseases, which also determine the severity of the coronavirus.

‘Make sure you have enough vitamin D in the blood’

For immunologist Carla Peeters, the new studies come as no surprise: “Low vitamin D status has been more often associated with more serious respiratory infections, including flu viruses. So, with the preliminary associations found with the coronavirus, it is recommended that to ensure adequate vitamin D in the blood. “But it is never the only nutrient needed for a properly functioning immune system, she adds. “It’s often about a combination of factors that can weaken the immune system.”

Build a winter supply of vitamin D in the summer sun

Still, an early spring outbreak can be more dangerous due to reduced vitamin D. “The concentrations are too low for many people in the period from February to April and sometimes even too low for the highest risk groups, such as the elderly.”

“For a well-functioning immune system, it is important for all people to get into the sun every day, without burning. But even then, the question is whether the amount of vitamin D saved at the beginning of autumn is still available in the following spring. to have sufficient vitamin D. People for whom it is not possible to build up sufficient vitamin D through sunlight need supplementation. ”

Koert now considers the added evidence from the scientific literature quite convincing. “Also because of all the other health risks that come with it, people with a deficiency should consider taking supplemental vitamin D in addition to summer sun exposure.” He recommends that you consult the Nutrition Centre site, which provides advice on dosages.

There, care is important, Peeters concludes: “The amount of vitamin D required to achieve good concentration varies greatly from person to person.”

Translated – Source: