Severe Vitamin D Deficiency Linked to Recurrent Fever in Single Case Report

A case report published in BMC Nutrition describes a 52-year-old woman whose recurrent high-grade fever resolved completely after she received oral vitamin D supplementation for severe deficiency. The patient presented with a one-month history of recurrent fever peaking at 39.4 °C, accompanied by leukopenia, anemia, and systemic symptoms. According to the report, an exhaustive diagnostic workup excluded infectious, autoimmune, and neoplastic causes, and comprehensive investigations—including metagenomic sequencing of cerebrospinal fluid—ruled out the common etiologies of fever of unknown origin (FUO). A subsequent nutritional assessment then identified severe vitamin D deficiency, with a 25-hydroxyvitamin D level of 8.7 nmol/L, equivalent to 3.48 ng/mL, attributed to insufficient sun exposure. After supplementation began, her fever resolved entirely, and no recurrence was observed during an 18-month follow-up period, coinciding with normalization of her vitamin D levels.

The authors frame the case as evidence that severe vitamin D deficiency may be an underrecognized potential contributing factor in recurrent fever of unknown origin. Vitamin D is recognized for its immunomodulatory roles, and the report argues that nutritional assessment—specifically evaluation of vitamin D status—should be integrated into the standard diagnostic algorithm for FUO as a complementary component of the comprehensive workup. The authors suggest this approach may contribute to targeted treatment in comparable presentations. The article is being shared early to provide faster access to peer-reviewed, accepted research; it is citable and carries a permanent DOI, but this version remains subject to further edits and will be replaced by the final Version of Record.

Important caveats apply to how broadly these findings can be interpreted. This is a single-case report describing one patient, so it demonstrates an association between vitamin D repletion and fever resolution in this individual rather than establishing a causal effect or a treatment that can be generalized to other patients with FUO. FUO is by definition a diagnostic challenge, and the report itself emphasizes that infectious, autoimmune, and neoplastic etiologies must first be exhaustively excluded before nutritional causes are considered. The reported remission spanned 18 months of follow-up with normalized vitamin D levels, but the authors’ conclusion is framed as identifying a potential contributing factor and underscoring the importance of nutritional assessment, not as proof that vitamin D deficiency commonly causes recurrent fever.

The case adds to a wider body of literature on vitamin D status referenced in the journal’s related content, including retrospective analyses of vitamin D deficiency prevalence in Turkish adults, urban and rural residents in Tianjin, China, and participants in the Czech Republic. Within that context, the report’s central practical message is procedural rather than therapeutic: clinicians working through the FUO diagnostic algorithm may consider adding evaluation of vitamin D status to the workup once more common causes have been ruled out. For patients presenting with recurrent unexplained fever alongside findings such as leukopenia and anemia, the report suggests that a nutritional assessment revealing severe deficiency—as in this patient, whose 25-hydroxyvitamin D level of 8.7 nmol/L (3.48 ng/mL) was attributed to insufficient sun exposure—can identify a treatable contributor. The resolution of fever after oral supplementation, with no recurrence over 18 months, is the outcome on which the authors base their recommendation that such assessment be considered a complementary component of the comprehensive FUO diagnostic workup.

Subject of Research: A case report linking severe vitamin D deficiency to recurrent fever of unknown origin in a 52-year-old woman.

Article Title: A 52-year-old woman with recurrent fever of unknown origin: a case report

Article References: Cai, Y., Chen, Y., Cai, X., & Long, L. (2026). A 52-year-old woman with recurrent fever of unknown origin: a case report. BMC Nutrition. https://doi.org/10.1186/s40795-026-01519-6

Image Credits: AI Generated

DOI: 10.1186/s40795-026-01519-6

Keywords: vitamin D deficiency, fever of unknown origin, case report, FUO diagnostic workup, nutritional assessment, immunomodulation, 25-hydroxyvitamin D, oral supplementation, leukopenia, BMC Nutrition, year-old, woman