Association Between Vitamin D Levels and Long COVID Signs and Symptoms

Background: “Long COVID” refers to a condition in which individuals continue to experience persistent signs and symptoms even after recovering from the initial COVID-19 infection. Signs and symptoms that persist can affect multiple organs in the body. Vitamin D is an essential nutrient that plays a crucial role, particularly in the immune system, and may be linked to the development of long COVID. Objective: The study aimed to investigate the association between vitamin D levels and the prevalence of long COVID signs and symptoms in COVID-19 patients. Materials and Methods: The study enrolled 170 COVID-19 patients with mild signs and symptoms and confirmed COVID-Ag or RT-PCR tests. The subjects were aged 18–59 years. All patients had 25(OH)D levels measured within 60 days of COVID-19 diagnosis and had been followed for at least 3 months post-infection. Data collected included demographic characteristics, serum 25(OH)D levels, and self-reported long COVID signs and symptoms questionnaire responses. Results: The study results indicated a female-to-male ratio of 1.1:1 and a mean age of 45.87 ± 8.65 years; of these, 62.4% received three doses of the COVID-19 vaccine, and 64.7% developed long COVID. The most prevalent signs and symptoms were respiratory (55.3%), skin (50.6%), and general (39.4%). The median blood vitamin D level was 22.96 ng/mL, with 41.2% of subjects having insufficient levels, 30.6% having deficient levels, and 28.2% having sufficient levels. Patients with long COVID had significantly lower vitamin D levels compared with those without long COVID (21.52 ng/mL vs. 25.46 ng/mL; p < 0.05). Multivariable analysis found that vitamin D deficiency was significantly associated with overall long COVID signs and symptoms (Adj. OR, 5.80 [95% CI: 2.10, 16.13]). Additionally, vitamin D deficiency significantly increased the number of long COVID systemic signs and symptoms (Adj. IRR, 3.30 [2.12, 5.12]). Conclusion: Assessing and maintaining vitamin D levels, vitamin D supplementation, and sunlight exposure in COVID-19 patients can reduce the risk and severity of long-term COVID-19 signs and symptoms.