The World's Most Common Nutritional Deficiency
Iron deficiency is the most prevalent nutritional disorder in the world. The World Health Organization (WHO) estimates that over 1.6 billion people — approximately 25% of the global population — are affected by anaemia, with iron deficiency being the most common cause.
It disproportionately affects women of reproductive age, pregnant women, young children, and people in developing countries. But iron deficiency is also surprisingly common in developed nations — the NHS notes it is the most common type of anaemia in the UK, and the CDC reports that approximately 10% of women in the United States are iron deficient.
Why Iron Matters
Iron is essential for producing haemoglobin, the protein in red blood cells that carries oxygen from your lungs to every cell in your body. Without enough iron:
- Your body cannot produce enough healthy red blood cells
- Your tissues and organs do not receive adequate oxygen
- You feel tired, weak, and unable to concentrate
Iron is also critical for:
- Immune function — Iron-deficient individuals are more susceptible to infections (NIH)
- Brain function — Iron is needed for neurotransmitter synthesis and cognitive performance
- Temperature regulation — Iron-deficient people often feel cold
- Energy metabolism — Iron is required for cellular energy production
Symptoms of Iron Deficiency
Iron deficiency progresses through stages, and symptoms worsen as stores deplete:
Early Iron Deficiency (Depleted Stores, Normal Haemoglobin)
- Fatigue and low energy
- Difficulty concentrating or brain fog
- Reduced exercise tolerance
- Increased susceptibility to infections
Iron Deficiency Anaemia (Low Haemoglobin)
As the deficiency progresses to anaemia, symptoms become more pronounced:
- Persistent fatigue — The hallmark symptom. Not resolved by rest
- Pale skin, nail beds, and gums — Reduced haemoglobin causes visible pallor
- Shortness of breath — Especially during physical activity
- Rapid or irregular heartbeat — The heart compensates for reduced oxygen-carrying capacity
- Dizziness or lightheadedness
- Cold hands and feet
- Brittle nails — Spoon-shaped nails (koilonychia) are a classic sign
- Headaches
- Restless legs syndrome — The Mayo Clinic notes a strong association between iron deficiency and RLS
- Unusual cravings (pica) — Craving ice, dirt, or starch
- Sore or swollen tongue (glossitis)
- Difficulty swallowing (rare, in severe cases)
Blood Tests for Iron Deficiency
Several blood tests are used to assess iron status. Understanding what each measures helps you interpret your results:
Haemoglobin (Hb)
- Normal: 13.5–17.5 g/dL (men), 12.0–15.5 g/dL (women)
- Low haemoglobin confirms anaemia but does not identify the cause
- According to the WHO, anaemia is defined as Hb below 13 g/dL in men and below 12 g/dL in non-pregnant women
Ferritin
- Normal: 20–250 ng/mL (men), 10–120 ng/mL (women)
- The most sensitive marker for iron deficiency
- Below 30 ng/mL strongly suggests iron deficiency, even with normal haemoglobin (NIH)
- Below 15 ng/mL is diagnostic of iron deficiency
Important caveat: Ferritin is also an acute phase reactant — it rises during infection, inflammation, and chronic disease. A "normal" ferritin in someone with active inflammation may actually mask underlying iron deficiency. The British Society for Haematology recommends using a ferritin threshold of 100 ng/mL in the presence of inflammation.
Serum Iron
- Normal: 60–170 mcg/dL
- Measures the amount of iron currently circulating in your blood
- Fluctuates throughout the day and with meals — less reliable than ferritin as a standalone test
Total Iron Binding Capacity (TIBC)
- Normal: 250–400 mcg/dL
- Measures how much transferrin (iron transport protein) is available to carry iron
- Elevated TIBC indicates iron deficiency — your body is making more transporters because there is not enough iron to go around
Transferrin Saturation
- Normal: 20–50%
- Calculated as (serum iron / TIBC) x 100
- Below 20% supports iron deficiency diagnosis
- More reliable than serum iron alone
Mean Corpuscular Volume (MCV)
- Normal: 80–100 fL
- Measures the average size of your red blood cells
- Low MCV (microcytic anaemia) is characteristic of iron deficiency
- Normal or high MCV with anaemia suggests other causes (B12 or folate deficiency)
Who Is at Risk?
According to the NIH Office of Dietary Supplements, high-risk groups include:
- Women with heavy menstrual periods — The most common cause of iron deficiency in premenopausal women
- Pregnant women — Iron requirements increase significantly during pregnancy
- Vegetarians and vegans — Plant-based (non-heme) iron is less well absorbed than animal-based (heme) iron
- Frequent blood donors
- People with GI conditions — Coeliac disease, inflammatory bowel disease, and gastric bypass reduce iron absorption
- Infants and young children — Rapid growth increases iron demands
- Endurance athletes — Particularly runners (footstrike haemolysis)
How to Improve Iron Levels
Dietary Sources
The NIH recommends 8 mg/day for adult men and 18 mg/day for premenopausal women.
Heme iron (best absorbed, from animal sources):
- Red meat, liver, and organ meats
- Poultry (dark meat)
- Shellfish — oysters, clams, mussels
- Fish — sardines, tuna
Non-heme iron (from plant sources):
- Spinach, kale, and Swiss chard
- Lentils, chickpeas, and beans
- Tofu and tempeh
- Fortified cereals and breads
- Pumpkin seeds and quinoa
Absorption Tips
- Pair iron-rich foods with vitamin C — Citrus fruits, tomatoes, and bell peppers significantly increase non-heme iron absorption (NIH)
- Avoid calcium, tea, and coffee with iron-rich meals — These inhibit absorption
- Cook in cast iron — Small amounts of iron leach into food during cooking
- Space iron supplements from dairy and antacids by at least 2 hours
When Supplements Are Needed
The Mayo Clinic recommends iron supplementation when:
- Ferritin is below 30 ng/mL with symptoms
- Haemoglobin is below the WHO-defined anaemia threshold
- Dietary changes alone are insufficient
- The underlying cause of deficiency is ongoing (heavy periods, GI malabsorption)
Note: Iron supplements can cause side effects (constipation, nausea, dark stools). Work with your doctor to find the right form and dosage.
Using AI to Track Your Iron Levels
Interpreting iron studies requires looking at multiple markers together — haemoglobin, ferritin, TIBC, transferrin saturation, and MCV — not just one number in isolation.
Symplicured can analyse your complete blood count and iron panel, explain what each marker means, and identify patterns consistent with iron deficiency — even in early stages before anaemia develops.
Key Takeaways
- Iron deficiency is the most common nutritional deficiency worldwide
- It progresses through stages — symptoms appear before anaemia develops
- Ferritin is the most sensitive marker — levels below 30 ng/mL suggest deficiency
- Multiple blood tests (ferritin, TIBC, transferrin saturation, MCV) provide the full picture
- Heme iron (from animal sources) is better absorbed, but plant sources are effective when paired with vitamin C
- AI tools like Symplicured can help you interpret your iron panel results in context
Upload your blood test to Symplicured to check for iron deficiency. Our AI analyses your haemoglobin, ferritin, and iron panel results — explaining what they mean and whether you should talk to your doctor.
