Does Vitamin D Deficiency Cause Low-Grade Fever? Exploring the Immunity-Inflammation Link

October 11, 2025 •

4 min read

While vitamin D is widely recognized for its crucial role in bone health, its profound impact on the immune system is often overlooked. This immunomodulatory function is central to understanding whether vitamin D deficiency can cause low-grade fever and other symptoms related to illness.

Quick Summary

Vitamin D deficiency does not directly cause a fever; instead, it weakens the immune system and promotes chronic inflammation, increasing susceptibility to infections. The low-grade fever may, therefore, be a symptom of a secondary infection or inflammatory response rather than the deficiency itself.

Key Points

Indirect Link, Not Direct Cause: Vitamin D deficiency itself does not cause low-grade fever, but it can weaken the immune system, making infections more likely.
Compromised Immunity: Low vitamin D levels impair the function of immune cells, reducing the body's ability to fight off bacteria and viruses effectively.
Increased Chronic Inflammation: Deficiency can lead to a state of chronic, low-grade inflammation, which is a known risk factor for various illnesses that can include fever.
Fever is a Symptom of Underlying Illness: When fever occurs in a person with low vitamin D, it is most likely a symptom of an underlying infection, not the vitamin deficiency itself.
Boost Immunity to Prevent Fever: Correcting a vitamin D deficiency through diet, sunlight, and supplements can strengthen the immune system and reduce the incidence of infections that cause fever.
Distinguish Fever vs. Feeling Cold: It's important to distinguish an actual fever from the feeling of coldness, which is another possible symptom of vitamin D deficiency.

The indirect connection between vitamin D deficiency and fever

A low-grade fever, typically defined as a body temperature slightly above the normal range ($98.6^{\circ}$F or $37^{\circ}$C) but below a more significant fever threshold, is not a direct symptom of vitamin D deficiency. Instead, the connection is indirect and related to the vitamin's critical role in immune function and regulation of inflammation. When vitamin D levels are low, the body's defenses are compromised, leaving it more vulnerable to infections that can trigger a fever as a natural response. Furthermore, a deficiency can promote a state of chronic, low-grade inflammation, which is another process that can potentially influence body temperature regulation.

Vitamin D's role in the immune system

Vitamin D is not just a vitamin; it also acts as a hormone that modulates the innate and adaptive immune systems. A wide variety of immune cells, including macrophages, monocytes, T cells, and dendritic cells, have vitamin D receptors (VDR) that are activated by the vitamin's active form, 1,25-dihydroxyvitamin D.

Key functions of vitamin D in immunity include:

Enhancing innate immunity: It promotes the production of antimicrobial peptides, such as cathelicidin, which can directly kill bacteria and viruses.
Modulating adaptive immunity: It influences the behavior of T cells, suppressing pro-inflammatory responses and promoting more regulatory ones. This helps the immune system respond appropriately without overreacting.
Regulating inflammation: As an immunomodulator, vitamin D helps to regulate the inflammatory cascade by influencing the production of cytokines and other inflammatory mediators.

When vitamin D levels drop, these immune functions become impaired. The body's ability to fight off pathogens is reduced, leading to an increased frequency of illnesses like respiratory tract infections, which are often accompanied by fever.

The impact on chronic inflammation

Beyond susceptibility to acute infections, vitamin D deficiency is strongly linked to chronic, low-grade inflammation. This is a persistent, systemic inflammatory state that can contribute to a range of chronic diseases.

Studies have shown a causal link between low vitamin D and elevated C-reactive protein (CRP), a widely used biomarker for chronic inflammation. The relationship is particularly strong in individuals with clinically deficient levels, suggesting that correcting the deficiency can reduce this baseline inflammation. While chronic inflammation may not always manifest as a noticeable fever, it indicates a physiological state where the body is in a constant, low-level fight, which can subtly affect body temperature regulation over time.

The diagnostic challenge: Differentiating causes of low-grade fever

Distinguishing a fever caused by an infection (made more likely by vitamin D deficiency) from other possible causes can be challenging. An isolated, persistent low-grade fever should prompt investigation into other potential underlying issues beyond simple vitamin deficiency.

Here is a comparison of signs that may help differentiate a fever caused by an infection from symptoms commonly associated with a vitamin D deficiency:


Symptom/Cause	Low-Grade Fever from Secondary Infection (common with deficiency)	Primary Symptom of Vitamin D Deficiency	Additional Note
Onset	Acute, often sudden	Gradual, chronic, often unnoticed	Deficiency-related fatigue can worsen suddenly with an infection
Fever Presence	Yes, fluctuating slightly above normal	No, deficiency itself does not cause fever	Feeling cold is a distinct symptom of low vitamin D, not a fever
Associated Symptoms	Body aches, chills, fatigue, cough, sore throat	Fatigue, bone/muscle pain, mood changes, hair loss	The presence of typical illness symptoms points to an infection
Immune Response	Heightened activity, fighting pathogens	Impaired and dysregulated immune function	The deficiency makes the body less effective at fighting off the infection
Underlying Issue	A specific bacterial or viral infection	Chronic low vitamin D status	The deficiency is the predisposing factor, not the direct cause

How to address vitamin D deficiency

Addressing a vitamin D deficiency is the most effective way to bolster your immune system and mitigate the indirect risks associated with low-grade fever. The primary methods for raising vitamin D levels include:

Sunlight Exposure: Sensible sun exposure is a natural and effective way for the body to produce vitamin D. The amount needed varies based on skin tone, latitude, and time of year. Short, frequent periods of sun exposure are often recommended.
Dietary Sources: While few foods are naturally rich in vitamin D, options include fatty fish like salmon, mackerel, and sardines, as well as egg yolks and beef liver.
Fortified Foods: Many dairy products, cereals, and orange juices are fortified with vitamin D.
Supplementation: For those with a confirmed deficiency, high-dose supplements are often necessary to restore levels. Dosage should be determined by a healthcare provider based on a blood test. Some research has shown that supplementation can effectively resolve fevers related to infections in deficient individuals.

Conclusion

In summary, while vitamin D deficiency does not directly cause a low-grade fever, it plays a critical indirect role. By compromising the immune system and contributing to chronic inflammation, a deficiency can make an individual more susceptible to infections that ultimately lead to fever. Correcting a vitamin D deficiency through sun exposure, diet, and supplementation is a proactive way to support a robust immune system and reduce the likelihood of these secondary health issues. Anyone with a persistent low-grade fever should consult a healthcare provider for a comprehensive evaluation to identify the root cause.

Additional resources

For more information on the wide-ranging effects of vitamin D on health and the immune system, you can explore resources from the National Institutes of Health.

Note: The content provided is for informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Frequently Asked Questions

Vitamin D deficiency itself doesn't cause a fever, but it can compromise your immune system, making you more susceptible to infections. The fever and general feeling of sickness would be caused by the subsequent infection, not the low vitamin D levels directly.

Low vitamin D impairs the function of immune cells like macrophages and T cells. This weakens the body's first line of defense and reduces its ability to regulate inflammatory responses, leaving it more vulnerable to pathogens.

If a persistent low-grade fever is caused by a chronic infection or an inflammatory state exacerbated by vitamin D deficiency, then correcting the deficiency and treating the underlying cause could help resolve the fever. For example, a study in children with tuberculosis showed that vitamin D supplementation helped improve fever resolution.

Common symptoms include fatigue, bone and muscle pain, weakness, poor sleep quality, mood changes like depression, and frequent illness or infections. Severe long-term deficiency can also cause bone loss (osteoporosis).

A blood test, specifically measuring 25-hydroxyvitamin D [25(OH)D], is the most common way to diagnose a deficiency. A healthcare professional can order this test if a deficiency is suspected.

Yes. Research has found a causal link between low vitamin D levels and elevated inflammatory markers, such as C-reactive protein (CRP). Correcting the deficiency can help reduce chronic, low-grade inflammation.

Treatment typically involves a combination of safe sun exposure, increasing intake of vitamin D-rich or fortified foods, and taking supplements. A doctor can recommend the appropriate dosage based on the severity of the deficiency.