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Denmark’s infection control agency: Low levels of vitamin D linked to serious COVID-19 infections

Denmark’s infection control agency: Low levels of vitamin D linked to serious COVID-19 infectionsVitamin D is of vital importance to a well-functioning immune defense and it protects against virus infections. This has been confirmed by Denmark’s infection control agency, Statens Serum Institut, and researchers from Harvard University in Boston, USA. In a study, the Danish and American scientists found that having low levels of vitamin D in the blood is associated with a greater risk of severe disease outcome in patients with COVID-19.

There has been a lot of discussion among scientists about whether vitamin D protects against infections such as COVID-19. Therefore, a team of scientists from Statens Serum Institut (Denmark’s infection control agency) and Harvard University in Boston conducted a study to determine if there is a link between vitamin D levels in the blood and the severity of a COVID-19 infection. The researchers analyzed blood samples that were stored in Denmark’s National Biobank (DNB). The blood samples had been taken from 447 Danes who had tested positive for SARS-CoV-2 in the spring of 2020. By combining the results of the 447 blood samples with information gathered from the National Patient Register, the scientists found the following:

  • 126 people were not hospitalized (28 %).
  • 205 where hospitalized but not admitted to intensive care (46 %).
  • 34 people were admitted to intensive care (8 %).
  • 82 people died within 30 days of testing positive (18 %).

The scientists conducted further analyses of the blood samples and patient information and concluded that having insufficient levels of vitamin D in the blood (below 50 nmol/L) was linked to a two times greater risk of experiencing a more severe disease outcome.

  • Low levels of vitamin D in the blood doubles the risk of a more severe outcome of a COVID-19 infection

How does vitamin D protect against COVID-19 and other infections?

It is commonly known that vitamin D is important for the innate immune defense that protects us against most microbes without causing any noticeable symptoms. Also, vitamin D is important for the adaptive immune defense that forms immunity. According to the new study, vitamin D protects against cytokine storm and an overactive immune reaction, which is what occurs in complicated COVID-19 cases.
Vitamin D also contributes to the formation of antibiotic peptides in the respiratory tract and the activation of genes. The scientists mention that genetic variations in a vitamin D-binding gene (SNPrs7041) may influence the severity of COVID-19. In other words, genes may affect how well we utilize vitamin D. The study is published in the science journal Scientific Reports.

  • The new study by Danish and American scientists supports earlier studies of vitamin D, the immune defense, and COVID-19

Widespread lack of vitamin D, especially during the winter

The strong sunshine during the summer period is our best source of vitamin D. The diet only contributes with a very small amount of the vitamin. An estimated one billion people worldwide lack vitamin D due to factors such as too little sun exposure (especially during the winter), ageing, being dark-skinned, being overweight, or having type 2 diabetes or other chronic diseases.

Vitamin D requirements and official recommendations

The Danish health authorities recommends for everyone to take a daily vitamin D supplement during the winter period. Moreover, it is recommended that vulnerable groups supplement with vitamin D all year round. These groups include people who get too little sunshine, children under four years of age, people with dark skin, pregnant women, nursing home residents, seniors from 70 years and older, and people at increased risk of osteoporosis.
The official recommendation for daily vitamin D intake lies in the range of 5-20 micrograms. Several studies suggest that this is not enough to ensure optimal blood levels of the nutrient, which should ideally lie in the range of 75-150 nmol/L. It is a good idea to have your blood levels measured. Beware that levels of vitamin D in the blood go down during the winter period unless you take a supplement.
Our synthesis and utilization of vitamin D is influenced by age, skin color, genes, BMI, overweight, and chronic diseases, which means that some people have a greater need than others for a vitamin D supplement to optimize their blood levels of vitamin D. According to the European Food Safety Authority (EFSA), the safe upper intake level for vitamin D is 100 micrograms daily. Most light-skinned people are able to synthesize that amount on a summer day with a clear, blue sky.


Statens Seruminstitut. Danskere med lavt D-vitamin niveau havde alvorlige forløb med covid-19.Nete Munk Nielsen et al. Vitamin D status and severity of COVID-19. Scientific Reports. 17 November 2022

Lacopo Chiodini et al. Vitamin D Status and SARS-CoV-2 Infection and COVID-19 Clinical Outcomes. Frontiers 22. December 2021

Helene Sandström. Den optimala D-vitamindosen i vinter? Det beror på dina genar. Nordic Nutrition Council. Sep. 3 2020

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