What is ferritin?

Ferritin is a protein that safely stores iron inside cells and releases it when needed. A small amount circulates in the blood, and this is what we measure on blood tests to estimate iron stores.

Low ferritin almost always reflects iron deficiency, even when haemoglobin levels are still within the normal range. At the same time, ferritin is also an acute-phase protein, meaning it rises during inflammation and infection. As a result, ferritin can appear “normal” or even elevated despite underlying iron deficiency when chronic inflammation is present.

Why iron matters for immunity

Iron is essential for immune cells. It is required for:

• rapid immune cell division,

• DNA synthesis,

• production of reactive oxygen species used to destroy pathogens,

• effective communication between immune cells via cytokines.

However, many pathogens also depend on iron for growth. To protect itself, the body uses a strategy known as nutritional immunity, sequestering iron inside ferritin and immune cells during infection to limit microbial access.

Because of this dual role, immune health depends on maintaining adequate but not excessive iron availability.

Low ferritin and infection risk

When ferritin and iron stores are low, immune function can be compromised. Research shows that iron deficiency can impair:

• neutrophil and macrophage activity,

• natural killer (NK) cell function,

• T-cell proliferation,

• antibody production.

Clinically, low ferritin has been associated with increased susceptibility to infections and slower recovery, even in the absence of overt anaemia.

Viral infections and ferritin

During acute viral infections, ferritin levels often rise as part of the inflammatory response. High ferritin in this context reflects immune activation rather than adequate iron stores and is frequently associated with more severe disease.

However, pre-existing low ferritin may weaken antiviral defences by limiting the immune system’s ability to mount an effective response. Iron deficiency has been linked to reduced T-cell activity and poorer antibody responses, which may affect both infection outcomes and vaccine responsiveness.

Fungal infections and iron balance

Fungal pathogens such as Candida and Aspergillus are particularly adept at acquiring iron from the host. The body responds by tightly binding iron within ferritin to restrict fungal growth.

At the same time, immune cells involved in antifungal defence — especially neutrophils and macrophages — rely on iron to generate the oxidative mechanisms needed to kill fungi. Severe iron deficiency may therefore impair antifungal immunity despite reduced iron availability to the pathogen.

Both clinical and experimental data suggest that iron deficiency and iron overload can increase susceptibility to fungal infections, highlighting the importance of balance.

The U-shaped relationship

Current evidence supports a U-shaped relationship between iron status and infection risk:

• Low ferritin → impaired immune cell function

• Excess iron → increased pathogen access and oxidative stress

Optimal immune function depends on adequate iron stores without chronic inflammation or overload.

Practical takeaways

• Low ferritin can weaken immune defences against viral and fungal infections.

• Normal or high ferritin does not always mean iron sufficiency, especially in inflammatory states.

• Iron supplementation should never be started without appropriate testing.

• Ferritin should be interpreted alongside haemoglobin, inflammatory markers, and clinical symptoms.

If you experience fatigue, frequent infections, hair shedding, or poor recovery from illness, assessing iron status may be an important part of understanding immune resilience.

If you would like support with testing, interpretation, or a tailored plan to optimise your iron status and immune health, Book a consultation with me.

Testing can be arranged where appropriate, and recommendations are always evidence-based and individualised.

References

• Abbaspour, N.R., Hurrell, R. and Kelishadi, R. (2014) ‘Review on iron and its importance for human health’, Journal of Research in Medical Sciences, 19(2), pp. 164–174. Available at: https://pubmed.ncbi.nlm.nih.gov/24778671/

• Drakesmith, H. and Prentice, A. (2012) ‘Hepcidin and the iron-infection axis’, Science, 338(6108), pp. 768–772. Available at: https://pubmed.ncbi.nlm.nih.gov/23139325/

• Cassat, J.E. and Skaar, E.P. (2013) ‘Iron in infection and immunity’, Cell Host & Microbe, 13(5), pp. 509–519. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC3676888/

• Ganz, T. (2015) ‘Iron homeostasis in host defence and inflammation’, Nature Reviews Immunology, 15(8), pp. 500–510. Available at: https://pmc.ncbi.nlm.nih.gov/articles/PMC4801113/

• Oppenheimer, S.J. (2001) ‘Iron and its relation to immunity and infectious disease’, Journal of Nutrition, 131(2S–2), pp. 616S–633S. Available at: https://pubmed.ncbi.nlm.nih.gov/11160594/

• Soares, M.P. and Weiss, G. (2015) ‘The iron age of host–microbe interactions’, EMBO Reports, 16(11), pp. 1482–1500. Available at: https://pubmed.ncbi.nlm.nih.gov/26474900/

• Weiss, G. (2002) ‘Iron and immunity: a double-edged sword’, European Journal of Clinical Investigation, 32(S1), pp. 70–78. Available at: https://pubmed.ncbi.nlm.nih.gov/12047329/