Ferritin explained: what is an optimal level for energy and health

Ferritin reflects the body's iron stores — but the standard lab range (15–300 µg/L) means you can be deeply iron-deficient without anaemia while hemoglobin is still normal. Here is what a functionally optimal ferritin looks like, why it drops and when it is truly too high.

What ferritin actually measures

Ferritin is the protein that stores iron in the liver, spleen and bone marrow. Serum ferritin reflects total body iron stores: 1 µg/L ≈ 8 mg of stored iron (Cook et al., Blood 2003). It is a more sensitive marker than hemoglobin — hemoglobin only drops once stores are already empty.

Lab range vs functional optimum

• Lab range: 15–300 µg/L (women), 30–400 µg/L (men)
• WHO iron-deficiency cutoff: < 15 µg/L (< 30 µg/L with chronic inflammation)
• Functional optimum (clinical literature): 70–150 µg/L
• Below 30 µg/L: fatigue, hair loss, restless-legs — before anaemia sets in (Soppi, 2018)

Why 'normal' is not the same as optimal

Ferritin 20 µg/L is formally 'normal' — but that is ~160 mg of stored iron, barely enough for a single menstrual cycle. Levels below 40–50 µg/L correlate with chronic fatigue, restless legs and hair loss even when hemoglobin is normal (Camaschella, NEJM 2015).

High ferritin — two very different causes

• Real iron overload: hereditary hemochromatosis, frequent transfusions — ferritin persistently > 300–500 µg/L, transferrin saturation > 45%
• Inflammation marker: ferritin is an acute-phase protein. Chronic inflammation, fatty liver (MAFLD), metabolic syndrome, infection all raise ferritin without actual iron excess (Kell & Pretorius, 2014)

What to test with ferritin

• Serum iron + transferrin + transferrin saturation (TSAT)
• Full blood count (Hb, MCV, MCH)
• hsCRP or CRP — inflammation falsely raises ferritin
• B12 and folate — commonly deficient in parallel
• TSH — hypothyroidism impairs iron absorption

Main causes of low ferritin

• Menstruation — the dominant cause in menstruating women
• Low meat intake / plant-based diet (non-haem iron absorbs 3–5× worse)
• Chronic low stomach acid (PPI use, atrophic gastritis)
• Coeliac disease or other small-bowel absorption issues
• Occult GI blood loss (ulcer, polyp) — always rule out in men > 40 and postmenopausal women

How to raise ferritin

Haem iron (red meat, liver) absorbs at 15–35%; non-haem iron at 2–10%. Vitamin C (100 mg with the meal) triples absorption. Coffee and tea block absorption — avoid within an hour before or after an iron-rich meal. Oral iron supplements raise ferritin by ~30–50 µg/L over three months; full replenishment usually takes 4–6 months.