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COVID-19 waves and vitamin D

- an overlooked connection

COVID-19 waves and vitamin DWhen it comes to battling COVID-19, the main focus is on hygiene, face masks, lockdown, and delayed vaccines. For several months, scientists have urged people to take vitamin D supplements during the winter period as a way of preventing new waves of COVID-19. This is because vitamin D is of vital importance for a well-functioning immune system and it is known that deficiencies of this nutrient contribute to the spread of seasonal virus infections. We also see that groups of people that are most likely to be vitamin D-deficient – including seniors, nursing home residents, people with dark skin, overweight individuals, diabetics, and those with chronic diseases – are most vulnerable towards COVID-19. The British government is already handing out vitamin D supplements to exposed groups, according to an article in Daily Mail and a review article that is published in British Medical Journal. But why is vitamin D so important for the immune defense, why are some people more likely to become deficient, and how much vitamin D do we actually need? Also, will vaccines cut the mustard if COVID-19 mutates?

It is common knowledge that the risk of contracting a virus infection is greater during the winter period because people spend more time indoors, often with little space between them. Nonetheless, several decades of scientific research suggest a link between seasonal virus infections and lack of vitamin D, which can weaken the immune defense and increase your risk of being infected.
The sun during the summer period is our main source of vitamin D and because the amount of vitamin D stored in the liver is limited, people living at northern latitudes tend to become vitamin D-deficient during the winter season. In fact, the first cases of COVID-19 were observed in Wuhan, China, after which the infection spread as a pandemic. As summer came along and people synthesized more vitamin D from sun exposure, the infection curve broke at northern latitudes. Ever since, researchers have warned against new infection waves in the winter due to increasing problems with vitamin D deficiency.
The British authorities are now taking the problem that seriously they have starting providing free vitamin D supplements for a four-month period to 2.2 million people in the most vulnerable part of the population. The aim of this is to boost their immune defense and, hopefully, be able to avoid constant lockdowns. Besides, the vaccines that have been introduced have limited effect if the virus mutates. The scientists there believe it is a better strategy to stimulate the immune defense in general.

Did you know that influenza and corona infections such as the common cold, SARS, and COVID-19 are caused by RNA virus that can easily mutate?

How vitamin D protects against virus infections in the airways

Vitamin D is important for both the innate and the adaptive immune system, which is designed to attack countless types of microorganisms. Vitamin D is also required for the body’s production of cathelicidin, defensin, and other antibiotic peptides that protect the respiratory tract. Because vitamin D regulates around 10 percent of our genes, the nutrient is vital for helping our white blood cells (T cells) divide explosively in order to fight infections swiftly and effectively. If we lack vitamin D, our white blood cells remain passive, which makes us more susceptible to infection at the same time as increasing the risk of us passing on the infection to others. This is what contributes to new waves of the infection.
What vitamin D also does is to make sure that we do not produce too many proinflammatory cytokines, and that is crucial during a COVID-19 infection. Lack of vitamin D increases the risk of an overreactive immune system with cytokine storm and hyperinflammation, which can result in acute respiratory distress syndrome (ARDS) and secondary damage to the circulatory system and other tissues. This can be potentially life-threatening.

  • The capacity of the immune defense determines whether we reject an infection, get a mild infection, or develop life-threatening complications
  • Eighty percent of patients hospitalized with COVID-19 are vitamin D-deficient, according to a study published in The Journal of Clinical Endocrinology & Metabolism
  • Patients that lack vitamin D are twice as likely to develop life-threatening complications in the wake of a COVID-19 infection, according to a study from Northwestern University, USA.

 We get most of our vitamin D from the sun – but deficiencies are widespread

When the sun sits high in the sky during the summer period, we are able to synthesize vitamin D in a process where UVB rays convert a cholesterol precursor in the skin into cholecalciferol (a vitamin D precursor). In the liver, cholecalciferol is converted in to 25-hydroxyvitamin D with help from enzymes. This is the form of vitamin D that is measured in the blood. When the body needs vitamin D, it converts 25-hydroxyvitamin D into the active form, 1,25-dihydroxyvitamin D. This conversion requires different enzymes. People who work outdoors during the summer period or who live in the middle of the United States (around the 41st parallel north) can typically produce around 70 micrograms of vitamin D on a sunny day. Dressed in a swim suit or completely naked, their vitamin D synthesis is increased by several hundred percent because much more skin is exposed to sunlight.
However, people’s vitamin D synthesis is limited by factors such as living at northern latitudes, spending too much time indoors, cloudy weather, congestive air pollution, veiling, wearing large-brimmed hats, having full beards, using face masks, and applying sunscreen with a high factor. The researchers also address the fact that sun awareness campaigns have made people avoid the sun out of fear of getting skin cancer. What is important in this connection is to avoid sunburns.
Vitamin D is also found in oily fish and liver but the average diet only provides limited quantities and certainly not enough to meet the official recommendations.

  • This time of year and at northern latitudes, the sun sits too low in the sky to enable us to synthesize vitamin D
  • A large Israeli population study of more than 4.6 million citizens has revealed that lack of sunlight and vitamin D increases the risk of COVID-19 infections and the occurrence of new waves during the winter period

Skin color and genetic variations

Being dark-skinned protects against sunburns but is also decreases your ability to synthesize vitamin D. In the United States, scientists have found that nearly all black Americans (97 percent) and the majority of Latinos from Mexico lack vitamin D.
According to Carsten Carlberg from the University of Eastern Finland, people react differently to vitamin D because of genetic differences. It is therefore not enough to measure the amount of vitamin D in your blood because the cells are unable to utilize the nutrient if it is not active. In theory it is the same with medical drugs to which people react entirely differently.

Ageing and nursing homes

Recent studies suggest that older people are able to synthesize the precursor of vitamin D in their somewhat thinner skin, but with age it becomes increasingly difficulty to active the nutrient in their kidneys. Another problem is that many seniors and nursing home residents spend far too little time in the sun. In fact, some never get outdoors. This is only made worse by problems like eating too little, avoiding oily fish and generally getting too little vitamin D from dietary sources.
Although the Danish Health Authority advises all people from 70 years and older to take 20 micrograms of supplementary vitamin D every day, people are generally not as compliant with vitamins as with medical drugs. What is more, there are no targeted campaigns for vitamin D in the fight against COVID-19.

Several studies in Denmark have shown that around 50 percent of the population has minor vitamin D deficiency, while around 15 percent of people are moderately deficient of the nutrient.

Overweight, metabolic syndrome, and diabetes

Overweight is spreading like a bushfire. Over half the Danish population is overweight. A meta-analysis of 18 studies found that overweight significantly inhibits blood levels of the nutrient and reduces the body’s ability to utilize vitamin D from supplements. On the other side, blood levels of vitamin D go up when overweight people go down in weight.
According to the scientists, overweight an affect levels of vitamin D in the blood in several different ways. Overweight, which is often combined with metabolic syndrome (an early stage of type 2 diabetes), tends to cause metabolic disturbances in the liver and kidneys, which the organs that help activate vitamin D. In addition, excess vitamin D is stored in our fatty tissue, which leaves it inaccessible to the blood and cells that need it.

In connection with COVID-19 and new infection waves, several researchers point to an alarming need for making sure that the population in general and vulnerable groups in particular get enough vitamin D to cover their individual needs.

Recommendations for general health and COVID-19

Most cells have vitamin D receptors. Besides being vital for the immune system, vitamin D is also important for our bones, blood sugar, circulatory system and for preventing cancer.
In Denmark, the official vitamin D recommendation for white adults up to the age of 70 years is 5 micrograms of vitamin D daily, while it is 10 micrograms in Great Britain and 15 micrograms in the United States. Several scientists suggest that even more is needed to ensure optimal blood levels of the nutrient.
A person’s actual need for vitamin D therefore hinges on multiple factors such as sun exposure, diet, genetic variations, skin color, ageing processes, BMI, diabetes, and other chronic diseases. Vitamin D supplements with 20-80 micrograms of vitamin D are available on the market.
EU’s Scientific Committee on Food has established the following safe daily upper intake levels for vitamin D: 25 micrograms for infants aged 0-6 months, 50 micrograms for children aged 6 months to 10 years, and 100 micrograms for children anyone older than 11 years of age, including pregnant and breastfeeding women. Vitamin D is lipid-soluble and is therefore has the best absorption in the body when taken in oil-filled gelatin capsules.


Glenn Owen. Elderly and vulnerable will get free Vitamin D from government. Daily Mail. November. 2020

Martin Kohlmeier. Avoidance of vitamin D deficiency to slow the COVID-10 pandemic. BMJ Nutrition, Prevention & Health. 2020

José L Hernandez et al. Vitamin D Status in Hospitalized Patients with SARS-CoV2- Infection. The Journal of Clinical Endocrinology & Metabolism. October 2020

Northwestern University. Vitamin D levels appear to play role in COVID-19 mortality rates. Science Daily. May 2020

Ariel Israel, Assi Circurel etb al. The link between vitamin D deficiency and COVID-19 in a large population. Department of Research and Data, Division of Planning and Strategy. 2020

Helene Sandström. Den optimala D-vitamindosen i vinter? Det beror på dina genar. Nordic Nutrition Council. Sep. 3 2020 Interview mit Dr. Carlberg: Vitamin D, Epigenetik und der Respons-Index. Hämtad. 2020-09-03

Jan Alexander et al. Early Nutritional Intervention with Zinc, Selenium and Vitamin D for Raising Anti-Viral resistance Against Progressive COVID-19. Nutrients 2020

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