Gallelli · Nutrients 2021 · multicenter comparative observational study · n=117

Vitamin D Serum Levels in Subjects Tested for SARS-CoV-2: What Are the Differences among Acute, Healed, and Negative COVID-19 Patients? A Multicenter Real-Practice Study.

Cited 30 times in the scientific literature.

Level 4 - case-series / case-control

Comparative observational study with an uncontrolled treated subgroup

PubMed 34836187 · doi:10.3390/nu13113932 · record verified 2026-08-31

What was done

A multicenter observational comparative study assessed serum 25(OH)D3 levels in 117 adult participants across three groups: acute COVID-19 infection, healed COVID-19, and non-infected controls between March and September 2021. The study also evaluated interleukin-6 (IL-6) levels in patients with severe vitamin D deficiency (<1 ng/mL) and in an uncontrolled subset administered active vitamin D (1α,25(OH)2D3).

What was found

Serum 25(OH)D3 was significantly lower in acute COVID-19 patients (9.63 ± 8.70 ng/mL) compared to non-infected controls (15.96 ± 5.99 ng/mL, p = 0.0091); healed patients had intermediate levels (11.52 ± 4.90 ng/mL, p > 0.05 vs. acute). Acute COVID-19 patients presented with elevated IL-6 (females: 127.64 ± 22.24 pg/mL; males: 139.28 ± 48.95 pg/mL), which dropped following 1α,25(OH)2D3 administration (to 1.84 ± 0.77 pg/mL and 2.65 ± 0.92 pg/mL, respectively).

Why it matters

This study provides real-practice observational data showing lower circulating 25(OH)D3 in acute COVID-19, offering hypothesis-generating data on inflammatory marker dynamics following active vitamin D administration.

Limits

The total sample size was small (n = 117), and the sample size for the supplemented subgroup was not reported in the abstract. The supplementation component lacked a randomized control group, making it impossible to determine if the IL-6 reduction was due to the intervention or the natural resolution of infection.

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