The Role of Vitamin D in the Context of the COVID-19 Pandemic
From the very first days of the COVID-19 pandemic, scientists seeking to understand why some people were more resistant to infection than others began actively investigating the possible role of vitamin D in the immune system. Vitamin D is a nutrient that the body can obtain from food or dietary supplements, and it can also be synthesized in the skin when it is exposed to sunlight.
It is well known that vitamin D contributes to the normal functioning of the immune system through various mechanisms, including the body’s ability to respond to viruses and other pathogens. “Vitamin D is inexpensive, widely available, and relatively safe,” says genetic epidemiologist Fotios Drenos from Brunel University London. According to him, the question of whether vitamin D could influence the course of COVID-19 was particularly important at the beginning of the pandemic.
Scientists had already established that vitamin D may help reduce the risk of respiratory tract infections. A 2017 meta-analysis of 25 randomized clinical trials involving approximately 11,000 participants showed that daily or weekly supplementation with vitamin D reduced the risk of acute respiratory tract infections. The greatest benefit was observed in individuals who had a marked vitamin D deficiency at the start of the studies.
This meta-analysis was led by Adrian Martineau from Queen Mary University of London. It was later updated to include data from 46 studies involving 75,500 participants. While the research team confirmed earlier conclusions about the importance of vitamin D for immune function, more recent data showed that the effect of supplementation was somewhat smaller than initially thought.
Epidemiological data collected during the early stages of the pandemic also suggested that vitamin D might be beneficial. People over the age of 65, individuals with lighter skin, and those with darker skin tones are more likely to have lower levels of vitamin D in the body. These groups also faced a higher risk of COVID-19, although the reasons for their vulnerability differed. In addition, studies showed that countries located farther from the equator, where sunlight exposure is lower, had higher COVID-19 mortality rates than countries closer to the equator.
In summary, these data are far from conclusive, but they provided an important incentive for further research into the interaction between vitamins and immune system resistance to the COVID-19 virus. It is also important to note that several large-scale vitamin D studies were already underway at the start of the pandemic and later became significant sources of information.
Scientific Evidence on Vitamin D
In Brisbane, Australia, cancer researcher Rachel Neale from the QIMR Berghofer Medical Research Institute led the so-called “D-Health Study.” This was a randomized, placebo-controlled trial involving 21,315 older adults who took vitamin D for five years.
The study compared high monthly doses of vitamin D (60,000 IU) with a placebo, assessing various health outcomes including heart disease, cancer, bone fractures, and overall mortality. Acute respiratory tract infections were also among the measured outcomes. During the COVID-19 pandemic, the researchers decided to analyze these data ahead of schedule.
The analysis, published in The Lancet Diabetes & Endocrinology, showed that vitamin D did not significantly reduce the risk of acute respiratory tract infections, but it may have slightly shortened the duration of symptoms. However, Rachel Neale emphasized that vitamin D levels in Australia are generally higher due to longer periods of sunlight, meaning that supplementation may have a smaller effect than in less sunny regions.
Another researcher who focused early on vitamin D during the pandemic in more northern latitudes is health economist and University of Chicago professor of medicine David Meltzer. He noted that historical vitamin D test results were available for hospital patients, allowing comparisons between COVID-19 test outcomes and vitamin D levels in the body.
An analysis of data from 4,638 individuals, published in JAMA Network Open, showed that among Black participants with low vitamin D levels, the risk of testing positive for COVID-19 was 2.64 times higher than among those with adequate levels. No significant correlation was observed among White participants. According to Meltzer, Chicago’s geographic location, long winters, and a higher proportion of people with darker skin made this association more apparent.
Overall, study results remain inconsistent, which may be due to differences in study design, already sufficient vitamin D levels in some populations, small sample sizes, or inconsistencies in dosing and measurement methods. Nevertheless, an increasing number of studies are currently examining vitamin D levels across different age groups, geographic locations, racial diversity, and COVID-19 antibody levels.
COVID-19 and Supporting the Immune System with Vitamins
A properly functioning immune system is crucial in the fight against COVID-19. To maintain normal immune function, the body requires adequate amounts of vitamins and micronutrients—yet many people often lack them.
Wearing masks, maintaining physical distance, and practicing good hand hygiene remain important protective measures. However, an equally important factor that has long received too little attention is a well-functioning immune system.
Biochemist Adrian Gombart from the Linus Pauling Institute at Oregon State University, together with his colleagues, prepared a review summarizing research on the effects of various nutrients on the immune system. According to him, without sufficient vitamins and micronutrients, the immune system cannot function effectively.
Vitamin D and Immune Defense
Scientific research shows that vitamin D is involved in regulating genes associated with the production of antimicrobial peptides. These peptides are an important part of the body’s nonspecific defense mechanisms. A deficiency in vitamin D can weaken these protective processes, making the body more vulnerable to external threats.
Vitamin C – an Important Component of Immunity
Vitamin C is essential for the immune system, as it participates in the formation of reactive oxygen species, antibody production, and other defense reactions. For these reasons, vitamin C is often cited as a key micronutrient in maintaining normal immune function.
Food or Dietary Supplements?
Although a balanced diet can theoretically provide sufficient nutrients, in practice additional vitamin intake may be relevant for certain population groups, such as older adults, pregnant women, and breastfeeding mothers. The German Federal Institute for Risk Assessment emphasizes that dietary supplements should not replace a balanced diet, but acknowledges that in certain situations they may help ensure an adequate intake of micronutrients.
Is It Possible to Overdose on Vitamin C?
Vitamin C is water-soluble, so severe overdose is rare. However, very high doses can cause adverse effects such as digestive discomfort. The established upper recommended limit for vitamin C intake in adults is 2,000 mg per day. Before taking higher doses or combining supplements with medications, it is recommended to consult a healthcare professional.
Sources:
Scientific American
Healthline
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