Vitamin D’s protective role in myocarditis following COVID-19 vaccines

It is well known and widely recognized that COVID-19 vaccines in rare cases can cause an important complication called myocarditis, which is inflammation of the heart muscle. However, according to a study published in Frontiers in Immunology, vitamin D appears to play a protective role by regulating the immune system’s inflammatory reaction.

COVID-19 vaccination has now been in use for several years, with more than 13.6 billion doses administered worldwide. One reported complication after vaccination is myocarditis, caused by exaggerated inflammatory processes in the heart muscle. Most cases have occurred in teenagers and young men, typically within a few days after they have received the vaccination.
As mentioned, myocarditis arises from intensified inflammatory responses, which in severe cases can damage the heart and become life-threatening. Vitamin D is known to help regulate these inflammatory processes by modulating NK cells (white blood cells) and other mechanisms.
The researchers hypothesized that myocarditis related to COVID-19 vaccination could be linked to vitamin D deficiency and decided to investigate this association further.
The study included 50 young men and 10 women who had received the mRNA COVID-19 vaccine (BNT162b2). Most patients developed acute myocarditis after receiving the second vaccine dose. Researchers collected various data and blood samples through the Hong Kong Hospital Authority (HA) to assess patients’ conditions, symptoms, and vitamin D status.
Most patients (88%) reported chest pain. Between 20–30% experienced fever, palpitations, and shortness of breath. About 30% were admitted directly to the intensive care unit due to severe complications.
The study found that the majority of patients (73%) had vitamin D deficiency. This deficiency was particularly common among those with chest pain and those admitted to intensive care. Vitamin D deficiency was also negatively associated with levels of cardiac troponin T, a protein released into the blood when heart muscle cells are damaged. Furthermore, deficiency correlated with higher levels of proinflammatory cytokines (IL-1β, IL-6, IL-8, IL-10, IL-12), which can cause overreaction of immune cells, including NK cells, in inflammatory processes. Patients with sufficient vitamin D levels had higher levels of IL-4, an anti-inflammatory cytokine.
These findings support the researchers’ hypothesis that vitamin D plays a crucial role in reducing COVID-19 vaccine-related adverse effects, such as myocarditis.

Vitamin D’s role in vital and potentially dangerous inflammation

The immune system is designed to trigger rapid inflammatory responses in the presence of infection. It is essential that these responses are properly regulated and contained in time to prevent damage to cells and tissues. Inflammatory processes are largely controlled by various cytokines, which can either be proinflammatory or anti-inflammatory. In this study, researchers focused particularly on NK cells from the innate immune system because these white blood cells, through the production of proinflammatory cytokines, may contribute to myocarditis following COVID-19 vaccination.
The study shows that vitamin D helps regulate inflammation via NK cells that have vitamin D receptors. Vitamin D receptors have also been found in other white blood cells, including monocytes, macrophages, dendritic cells, and activated T cells. This means vitamin D plays multiple critical roles in both preventing and controlling infections, thereby ensuring that inflammatory processes proceed normally.
However, this requires blood vitamin D levels above 75 nmol/L, or ideally around 100 nmol/L. It should be noted that the official recommendations of getting 5–20 micrograms of dietary vitamin D daily do not necessarily optimize blood levels or meet immune system needs for the nutrient. Since most of the body’s cells have vitamin D receptors and vitamin D has many essential functions, many individuals can benefit from higher supplementation - particularly during winter and in vulnerable groups such as older adults, diabetics, chronically ill patients, and people with dark skin, who have more difficulty with producing vitamin D in the skin or converting it into its active steroid form. Research also shows that these groups are more susceptible to COVID-19 infections, and vitamin D deficiency plays a key role.

Vitamin D deficiency increases the risk of COVID-19 and inflammatory diseases

The following article explores the importance of vitamin D for the immune system and how widespread deficiencies increase the risk of COVID-19 infections, other infectious diseases, and many chronic conditions associated with persistent inflammation.

»Vitamin D deficiencies are involved in COVID-19 infections, rheumatoid arthritis, diabetes, and other inflammatory diseases«

References:

Hing Wai Tsang et al. The protective role of vitamin D in BNT162b2 vaccine-related acute myocarditis. Frontiers in Immunology, 2025

Bach-dependent safety of the BNT162b2 mRNA COVID-19 vaccine. European Journal of Clinical Investigation. 2023