Research Tracker›Biomarker Atlas›Marker Pages›Vitamin D (25-OH)

Vitamin D (25-OH) across conditions

Vitamin D (25-OH) appears in 2 entries of the OSMF biomarker atlas, covering Gulf War Illness, Long COVID. Across those entries it is mixed in 2. Because the same marker shifts in several unrelated conditions, it is best understood as a signal of shared biology such as inflammation, vascular or metabolic stress rather than as a condition-specific test. Each row below links to a page with the comparison group, associated symptoms, test details and primary citation.

Gulf War IllnessLong COVID

Where Vitamin D (25-OH) is reported

Also listed as: Calcidiol

ConditionDirectionCompared againstAssociated symptomsSource
Gulf War Illness↕ inconsistenthealthy Gulf War veteran controlsImmune modulationGean et al. 2021
Long COVID↕ inconsistenthealthy controlsImmune modulationKallaste et al. 2025

Frequently asked questions

In which conditions is Vitamin D (25-OH) altered?

In the OSMF atlas Vitamin D (25-OH) is reported in Gulf War Illness, Long COVID. It is mixed in 2 across 2 entries.

Does Vitamin D (25-OH) point to one specific diagnosis?

No. Because Vitamin D (25-OH) changes in several conditions (Gulf War Illness, Long COVID), an abnormal result cannot identify which condition, if any, is present. It must be interpreted with symptoms, history and other tests.

What is the LOINC code for Vitamin D (25-OH)?

Entries in this atlas use LOINC 1989-3. LOINC codes identify the laboratory observation so results can be compared across systems.

Is one abnormal Vitamin D (25-OH) result diagnostic?

No single biomarker result is diagnostic of any of these conditions. Findings reflect group averages from published cohorts with substantial overlap between patients and controls.

Cite this page

Open Source Medicine Foundation. (2026). Vitamin D (25-OH) across conditions: biomarker evidence. OSMF Research Tracker. Retrieved October 7, 2026, from https://research.opensourcemed.info/biomarkers/markers/vitamin-d-25-oh.html
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Last reviewed: 2026-06-29 · Browse: Biomarker Index · All marker pages · Biomarker Atlas

Disclaimer: Educational synthesis of peer-reviewed research; not medical advice. Findings are group-level and vary with study design. Discuss any result with a qualified clinician.