Vitamin D supplementation can help chronic fatigue syndrome following COVID-19

Side effects such as chronic fatigue syndrome (CFS/ME), brain fog, sleep disturbances, and other neurological issues have been observed both after COVID-19 infections and vaccinations. According to a study published in Nutrition, most of these patients were already deficient in vitamin D, and higher doses of vitamin D that optimize blood levels can help relieve their symptoms. It’s generally advisable to maintain adequate vitamin D levels for the prevention of COVID-19, influenza, and other infections.

Since the COVID-19 pandemic began in 2020, various long-term effects and symptoms, collectively referred to as Post-COVID-19 or Long COVID, have been reported. These symptoms are the same as those seen in chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). In addition to extreme, persistent fatigue, patients may experience brain fog, sleep disturbances, pain, and other neurological issues.
The spike protein on the surface of the COVID-19 virus is believed to be responsible for many of these symptoms. This is because ACE2 receptors, to which the spike protein binds, are found throughout the body, including in endothelial cells lining the airways, blood vessels, and other tissues. When the spike protein binds to an ACE2 receptor, the virus can enter the cell, turning it into a virus-producing factory - unless the immune system destroys the virus upon first contact in the nasal mucosa.
Most COVID-19 infections are mild or asymptomatic. However, if the immune system does not neutralize the virus in the nasal mucosa on first contact and fails to generate immunity (especially via T-cells), COVID-19 can spread to the lungs, bloodstream, and other cells and tissues with ACE2 receptors.
COVID-19 vaccines are based on a new mRNA technology that instructs the body’s own cells to produce spike proteins. The vaccines aim to train the immune system to recognize these spike proteins and respond to COVID-19.
Vitamin D plays a key role in immune function, regulating inflammation, and supporting the brain and nervous system. Vitamin D deficiency is widespread. Therefore, researchers in this new study investigated the effect of vitamin D therapy in patients who developed CFS/ME symptoms following COVID-19 vaccination.

Patients experienced significant improvement with vitamin D therapy

The study included 28 patients who developed CFS/ME between August 2022 and February 2024 after receiving the COVID-19 vaccine. The severity of CFS/ME was assessed using a specific scale that measures various functional impairments.
At the start of the study, 27 of the 28 patients had vitamin D blood levels below 50 nmol/L (20 ng/mL), which is considered the lower limit. Optimal levels are ideally above 75 nmol/L.
Participants then received various forms of vitamin D therapy. They were advised to increase safe sun exposure and to consume vitamin D-rich foods such as fatty fish, cod liver, eggs, and butter. Most participants also took daily vitamin D supplements of 25-100 micrograms, far exceeding the official daily recommendations of 5-20 micrograms.
The study showed that vitamin D therapy raised all participants’ blood levels to around 75 nmol/L. There was a substantial reduction in CFS/ME symptoms, with average scores dropping from approximately 10 to 2 on the scale. Remarkably, 23 of the 28 patients (82%) no longer met the diagnostic criteria for CFS/ME. Vitamin D therapy had the greatest positive effects on sleep problems (71%) as well as brain fog and other autonomic nervous system symptoms.
The researchers concluded that vitamin D deficiency increases the risk of side effects from COVID-19 vaccines and that vitamin D therapy that optimizes blood levels can relieve or even eliminate many symptoms. They are now preparing a larger, randomized controlled study to evaluate the effect of vitamin D therapy for patients who develop CFS/ME after either vaccination or COVID-19 infection.

Key points:

• Vitamin D helps the immune system respond appropriately to spike proteins, preventing harmful inflammation.
• Vitamin D deficiency is widespread, and vitamin D therapy has a positive effect in preventing COVID-19, other infections, and vaccine-related side effects.

Reference:

Shinichiro Kodame et al. Efficacy of vitamin D replacement therapy on 28 cases of myalgic encephalomyelitis/chronic fatigue syndrome after COVID-19 vaccination. Nutrition 2025