Iron Deficiency: Symptoms, Causes, and How to Raise Your Levels (2026)

Iron deficiency is the world's most widespread nutritional deficiency — affecting an estimated 2 billion people globally, or roughly 25% of the world population. In developed countries, it's most common in women of reproductive age, pregnant women, infants, and athletes. Despite being so prevalent, it's frequently missed or undertreated — partly because its symptoms (fatigue, brain fog, reduced exercise capacity) are easy to attribute to other causes, and partly because testing is often incomplete.

Why Iron Is Essential

Iron's most critical role is in hemoglobin — the protein in red blood cells that transports oxygen from the lungs to every cell in the body. About 70% of the body's iron is found in hemoglobin and myoglobin (the oxygen-storing protein in muscles). When iron is insufficient, the body can't produce adequate functional hemoglobin, reducing oxygen delivery to tissues — the basis of anemia's symptoms.

Iron also serves as a cofactor for hundreds of enzymes involved in energy production, DNA synthesis, immune function, and neurotransmitter synthesis (dopamine, norepinephrine, serotonin all require iron-containing enzymes). This explains why iron deficiency causes such varied symptoms beyond anemia.

The Stages of Iron Deficiency

Iron deficiency develops progressively through three stages, each more severe:

A critical point: you can have significant iron deficiency (stages 1 and 2) with a normal hemoglobin. A "normal" CBC doesn't rule out iron deficiency — ferritin must be measured. Many people have their iron checked, are told "your iron is fine," and actually have significant ferritin depletion that explains their symptoms. Always ask for ferritin specifically.

Symptoms of Iron Deficiency

Most Common

• Fatigue and low energy: The hallmark symptom — often described as bone-deep exhaustion not proportional to activity
• Reduced exercise tolerance: Becoming breathless with exertion that previously felt easy
• Brain fog and difficulty concentrating
• Pale skin, pale inner eyelids, pale gums
• Cold hands and feet
• Headaches
• Dizziness or lightheadedness

Specific Signs Worth Knowing

• Pica: Cravings for non-food substances — most commonly ice (pagophagia), but also dirt, chalk, or starch. Pica is a surprisingly specific marker of iron deficiency and should prompt immediate testing
• Restless legs syndrome: Iron deficiency is one of the most common secondary causes of RLS — the uncomfortable urge to move legs, particularly at night
• Koilonychia: Spoon-shaped nails — a classic but late sign of severe deficiency
• Hair loss: Ferritin below 30 ng/mL is associated with telogen effluvium (diffuse hair shedding) in women
• Glossitis: Smooth, sore tongue
• Angular cheilitis: Cracks at the corners of the mouth

Common Causes

Inadequate Intake

The RDA for iron is 8 mg/day for adult men and postmenopausal women, rising to 18 mg/day for premenopausal women and 27 mg/day during pregnancy. Plant-based diets and diets low in meat often provide primarily non-heme iron, which has significantly lower bioavailability than heme iron from animal products.

Blood Loss

The most common cause of iron deficiency in women: menstruation. Heavy periods (losing more than 80ml per cycle) cause substantial monthly iron loss that dietary intake may not fully replenish. In men and postmenopausal women, new-onset iron deficiency anemia requires ruling out GI blood loss — peptic ulcers, colon polyps, colorectal cancer, or other sources — before assuming dietary cause.

Reduced Absorption

• Celiac disease — damages the duodenum where iron absorption primarily occurs
• Helicobacter pylori infection — impairs iron absorption through multiple mechanisms
• Inflammatory bowel disease
• After gastric bypass surgery
• Long-term antacid or PPI use (reduce stomach acid needed for iron reduction from Fe³⁺ to Fe²⁺)

Increased Demand

Pregnancy, rapid growth in adolescence, and endurance exercise (which increases red blood cell turnover and may cause small amounts of GI blood loss and foot-strike hemolysis) all increase iron requirements beyond standard dietary intake.

The Heme vs. Non-Heme Iron Distinction

Dietary iron comes in two forms with dramatically different absorption rates:

• Heme iron: Found in animal products (meat, fish, poultry) — absorbed at 15–35% efficiency regardless of other foods eaten
• Non-heme iron: Found in plant foods and iron supplements — absorbed at only 2–20% efficiency, highly dependent on what you eat with it

This is why vegetarians and vegans need approximately 1.8× more dietary iron than meat eaters, and why iron supplements may require significantly higher doses to correct deficiency than one might expect from the stated milligram amount.

Optimizing Non-Heme Iron Absorption

Several factors dramatically affect non-heme iron absorption:

• Vitamin C increases absorption 3-fold: Pairing iron-rich plant foods (lentils, spinach, fortified cereals) with vitamin C sources (citrus, bell peppers, tomatoes) in the same meal significantly improves absorption
• Meat factor: Eating small amounts of meat alongside plant iron sources increases plant iron absorption
• Avoid with iron: Calcium (dairy, calcium supplements), tannins (tea, coffee), phytates (in bran, whole grains), and polyphenols significantly reduce non-heme iron absorption — take iron supplements or eat iron-rich plant foods separately from these
• Coffee and tea: Can reduce iron absorption by 40–90% when consumed with meals — wait at least 1 hour after iron-rich meals before having tea or coffee

Best Iron-Rich Foods

Iron Supplements: Forms and Tolerability

When diet alone is insufficient to correct deficiency — which is often the case given absorption rates — supplementation is necessary:

• Ferrous sulfate: The most commonly prescribed form — effective and inexpensive, but frequently causes GI side effects (constipation, nausea, dark stools)
• Ferrous gluconate: Lower iron content per tablet but generally better tolerated than ferrous sulfate
• Ferrous bisglycinate (gentle iron): Significantly better absorbed and much better tolerated — less constipation and GI upset; available over-the-counter; worth the higher cost for those sensitive to standard iron supplements
• Liquid iron: Useful for those who can't swallow tablets and for children
• IV iron: When oral supplementation fails, causes excessive GI side effects, or when rapid correction is needed (severe anemia before surgery, severe pregnancy iron deficiency, inflammatory bowel disease where oral absorption is poor)

Research by Paul Zimmermann's group found that alternate-day iron supplementation (taking iron every other day rather than daily) produces comparable iron absorption to daily dosing with significantly better tolerability — because absorption is actually higher when hepcidin (an iron-regulating hormone) resets overnight between doses.

Frequently Asked Questions