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Low vitamin D levels lower immune response to COVID-19 vaccine

New research shows that low levels of vitamin D in individuals may result in an impaired or weakened immune response to the COVID-19 vaccine. This adds to the body of evidence that vitamin D has some complicated relationship with COVID-19.

This does not mean that you should swallow a handful of vitamin D capsules a few days before you get the COVID-19 vaccine or one of the boosters. It means that if one has a low level of vitamin D, as determined by a blood test, taking vitamin D supplements to increase the blood level of the vitamin may help boost the immune response to the vaccine.

As I usually do, I will review this new research and provide an analysis of the research.

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Vitamin D levels and COVID-19 vaccine research

In a paper published on 17 August 2023 in Endocrine, Andrea Giustina, Institute of Endocrine and Metabolic Sciences, San Raffaele Vita-Salute University and IRCCS Hospital, Milano, Italy, and colleagues examined whether low vitamin D levels contributed to an impaired immune response from the Pfizer-BioNTech COVID-19 vaccine.

The researchers developed a Retrospective cohort study that included 119 consecutive healthcare workers (median age 53) without a previous history of acute COVID-19 or lacked anti-SARS-CoV-2 immunoglobulins. They measured levels of calcifediol (also written as 25(OH)D), which is a form of vitamin D produced in the liver by the hydroxylation of vitamin D3 (cholecalciferol) by the enzyme vitamin D 25-hydroxylase, at the time of first immunization with the Pfizer-BioNTech vaccine.

The immune responses were evaluated at:

  • Before the first dose of the vaccine.
  • At the time of the second dose (which was 21 days after the first dose.
  • Then the immune response was measured at 1, 5, and 9 months after the second dose.

Median 25(OH)D levels in all participants were 25.6 ng/mL, and vitamin D deficiency (25(OH)D <20 ng/mL) was observed in 29 subjects (24.8%).

Here are the key results:

  • In those participants with a vitamin D deficiency, we found a non-significant trend towards lower antibody titers at five months, and significantly lower titers at nine months as compared to those who were not vitamin D deficient.
  • Researchers also observed a more pronounced antibody-titers drop from the time of the second dose to five months in those with vitamin D deficiency.
  • The researchers also found a positive correlation between vitamin D levels and COVID-19 antibody titers at five months.

The researchers concluded that low blood levels of vitamin D were linked to a lower antibody response to the COVID-19 vaccine.


This is an interesting first study that may show a link between vitamin D levels and the immune response to the COVID-19 vaccine. It may also show a link between vitamin D and the health of the immune system.

However, I need to make an important caveat — this research does not provide evidence that excess vitamin D levels suddenly make your immune system become the Superman of immune systems. In fact, excess vitamin D, called hypervitaminosis D, can lead to serious medical conditions such as over-calcification of bones, heart, and other tissue. This is not a good thing.

There is also another caveat — this was a small study using healthcare workers. I would prefer to see results from a much larger study (1000-3000) in a broader group of participants. Also, the researchers did not constantly monitor the vitamin D levels of the participants except prior to the first dose of the vaccine. I would like to see what the vitamin D levels compared to the antibody titers at each time point.

Although far from perfect, this study is very intriguing, and it gives me more reason to continue to monitor my blood vitamin D levels.

So, before you get your COVID-19 vaccine boosters this fall, you might want to have your blood levels of vitamin D checked, and take supplements if they’re low (if advised by your physician). Then get those boosters.


Michael Simpson

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