Clinical Characteristics of Vitamin D Deficiency Detected in Long COVID Patients During the Omicron Phase

Background: To characterize the clinical significance of vitamin D deficiency (VDD) detected in long COVID, a retrospective observational study was performed for outpatients who visited our clinic during the period from May 2024 to November 2024. Methods: Clinical trends in long COVID patients diagnosed with VDD who showed serum concentrations of 25-hydroxyvitamin D (25-OHD) lower than 20 ng/mL were compared with those in long COVID patients in a non-deficient vitamin D (NDD) group. Results: Of 126 patients with long COVID, 97 patients (female: 50) who had been infected during the Omicron phase were included. Sixty-six patients (68%) were classified in the VDD group. The median serum concentrations of 25-OHD were 14.8 ng/mL in the VDD group and 22.9 ng/mL in the NDD group. There were no significant differences between the two groups in terms of age, gender, BMI, severity of COVID-19, period after infection and vaccination history. Although the levels of serum calcium and phosphate were not significantly different between the two groups, the percentages of patients in the VDD group who complained of dizziness, memory impairment, palpitation and appetite loss were larger than those in the NDD group. Of note, the patients who complained of palpitation showed significantly lower concentrations of serum 25-OHD than those in the patients without palpitation (median: 11.9 vs. 17.3 ng/mL). Moreover, patients in the VDD group had significantly higher scores for physical and mental fatigue as well as higher scores for depressive symptoms. Conclusions: Collectively, VDD is involved in clinical manifestations of long COVID, particularly symptoms of palpitation, fatigue and depression.