Signs of Iron Deficiency (Anemia) and What to Do About It

The signs of iron deficiency are easy to dismiss because the symptoms — fatigue, weakness, feeling cold, difficulty concentrating — overlap with so many other common explanations: a busy schedule, poor sleep, stress, or just getting older. Yet iron deficiency is the most common nutritional deficiency in the world, affecting an estimated 25% of the global population to some degree, according to the World Health Organization.

This guide covers what iron actually does in the body, the signs of deficiency, who’s most at risk, how it’s diagnosed, and what treatment actually looks like.

What Iron Does in Your Body

Iron’s primary role is in hemoglobin — the protein in red blood cells that carries oxygen from your lungs to every tissue in your body. Without adequate iron, your body can’t produce enough healthy red blood cells, and oxygen delivery throughout the body becomes less efficient.

Iron also plays roles in:

• Energy production — iron is a cofactor in enzymes involved in cellular energy metabolism
• Immune function — iron-dependent enzymes support immune cell activity
• Cognitive function — the brain requires adequate oxygen delivery and iron-dependent neurotransmitter synthesis
• Muscle function — myoglobin, a protein similar to hemoglobin, stores oxygen in muscle tissue

When iron is insufficient, the body prioritizes hemoglobin production for survival — which means other iron-dependent functions (energy, cognition, immune response) are affected even before anemia becomes severe enough to show up on a basic blood count.

The Spectrum: From Low Iron Stores to Anemia

Iron deficiency develops in stages, and symptoms can appear before full-blown anemia is diagnosed:

Stage 1 — Depleted iron stores: Ferritin (the protein that stores iron) drops, but hemoglobin is still normal. Some people experience fatigue and reduced exercise tolerance at this stage even though a standard complete blood count (CBC) looks normal.

Stage 2 — Iron deficiency without anemia: Iron stores are low enough to start affecting red blood cell production, but hemoglobin remains within the normal range — often at the lower end.

Stage 3 — Iron deficiency anemia (IDA): Hemoglobin drops below normal range. This is what’s typically caught on a standard CBC. By this stage, symptoms are usually noticeable.

This staged progression is why some people feel unmistakably unwell with “normal” bloodwork — if only hemoglobin was checked and ferritin wasn’t, early-stage depletion can be missed entirely.

Signs and Symptoms of Iron Deficiency

1. Persistent Fatigue and Weakness

This is the most common symptom and often the first one people notice. Because oxygen delivery to tissues is reduced, the body simply has less capacity for sustained activity. This fatigue is often described as feeling “heavy,” different from normal tiredness, and not significantly improved by rest or sleep.

2. Pale Skin and Pale Inner Eyelids

Hemoglobin gives blood — and by extension, skin — its red color. Reduced hemoglobin can cause noticeable paleness, particularly visible in the inner lower eyelid (pulling down the lower eyelid reveals a pale pink to white color instead of a healthy red).

3. Shortness of Breath and Rapid Heartbeat

With less oxygen-carrying capacity, the heart and lungs work harder to compensate — leading to breathlessness during activities that wouldn’t normally cause it, and a heart rate that feels elevated even at rest.

4. Headaches and Dizziness

Reduced oxygen delivery to the brain can cause frequent headaches, lightheadedness, and dizziness — particularly when standing up quickly.

5. Brittle Nails and Hair Changes

Iron deficiency affects rapidly dividing cells, including those in hair follicles and nail beds. Signs include brittle, spoon-shaped nails (koilonychia — a classic but less common sign of more severe deficiency) and increased hair shedding.

6. Restless Legs Syndrome

There’s a well-documented association between low iron stores and restless legs syndrome (RLS) — an uncomfortable urge to move the legs, particularly at night. Research published in Sleep Medicine Reviews has found that correcting iron deficiency improves RLS symptoms in a significant proportion of cases.

7. Pica — Unusual Cravings

Pica refers to craving and sometimes eating non-food substances — most classically ice (pagophagia), but also dirt, paper, or starch. While the exact mechanism isn’t fully understood, pica is specifically associated with iron deficiency and often resolves once iron levels are corrected.

8. Cold Hands and Feet

Reduced circulation efficiency and the body’s prioritization of blood flow to vital organs can leave extremities feeling persistently cold.

9. Difficulty Concentrating (“Brain Fog”)

Cognitive symptoms — trouble focusing, slower processing, forgetfulness — are commonly reported and have been documented in research on iron deficiency, particularly in women of reproductive age and in children, where iron deficiency has measurable effects on cognitive development.

10. Frequent Infections

Iron plays a role in immune cell function, and some research suggests iron-deficient individuals may experience more frequent infections — though this association is less consistently documented than the other symptoms above.

Who Is Most at Risk?

Group	Why
Menstruating women	Regular blood loss is the most common cause of iron deficiency in this group
Pregnant women	Blood volume increases significantly; iron needs roughly double
Infants and young children	Rapid growth increases iron needs; breast milk is low in iron after 6 months
Vegetarians and vegans	Plant-based (non-heme) iron is less efficiently absorbed than iron from meat
People with GI conditions	Celiac disease, Crohn’s disease, and prior gastric bypass surgery reduce iron absorption
Frequent blood donors	Regular donation depletes iron stores over time
Endurance athletes	“Sports anemia” results from increased iron losses through sweat, GI tract, and red blood cell turnover
People with chronic blood loss	Including from ulcers, hemorrhoids, or — importantly — undiagnosed GI conditions

How Iron Deficiency Is Diagnosed

A standard complete blood count (CBC) checks hemoglobin and hematocrit — but ferritin is the key test for iron stores specifically, and it’s often the earliest marker to drop.

Test	What It Measures	Typical Reference Range (varies by lab)
Hemoglobin	Oxygen-carrying capacity of blood	~12–16 g/dL (women), ~13.5–17.5 g/dL (men)
Ferritin	Iron storage levels	~15–150 ng/mL (varies significantly by lab and sex)
Transferrin saturation	Percentage of iron-transport protein carrying iron	~20–50%
MCV (mean corpuscular volume)	Average red blood cell size — small (microcytic) cells are typical in iron deficiency	~80–100 fL

A ferritin level in the “low normal” range (for example, under 30 ng/mL) can still represent functional iron deficiency in someone with symptoms, even if it’s technically within the lab’s reference range. This is a common reason iron deficiency goes undiagnosed — the number looks “normal” without context.

Important: Ferritin is also an inflammatory marker — it can be falsely elevated during illness or inflammation, masking true iron deficiency. If you have symptoms and a borderline ferritin level, discussing additional markers (transferrin saturation, CRP) with your doctor provides a clearer picture.

Dietary Sources of Iron

Iron comes in two forms with different absorption rates:

Heme iron (from animal sources) — absorbed at roughly 15–35% efficiency:

• Red meat (beef, lamb)
• Liver and organ meats (very high in iron)
• Poultry (dark meat especially)
• Fish and shellfish (oysters, sardines, tuna)

Non-heme iron (from plant sources) — absorbed at roughly 2–20% efficiency, and absorption is affected by other foods eaten at the same time:

• Lentils, chickpeas, and other legumes
• Tofu and tempeh
• Spinach and other dark leafy greens
• Pumpkin seeds
• Fortified cereals and breads
• Quinoa

Boosting non-heme iron absorption: Vitamin C significantly increases non-heme iron absorption. Pairing iron-rich plant foods with a source of vitamin C — such as lentils with bell peppers, or spinach with citrus dressing — can meaningfully improve how much iron your body actually absorbs.

What reduces iron absorption: Coffee and tea (specifically the tannins) can reduce non-heme iron absorption by up to 50–60% when consumed with meals. Calcium-rich foods and supplements can also interfere with iron absorption when taken together. Separating these by an hour or two from iron-rich meals or supplements helps.

Iron Supplementation

If diagnosed with iron deficiency, your doctor may recommend an iron supplement. A few practical points:

• Ferrous sulfate, ferrous gluconate, and ferrous fumarate are common forms. Gentler forms (like iron bisglycinate) cause less GI upset for some people but may be more expensive.
• Common side effects include constipation, nausea, and dark-colored stool — generally not harmful but worth knowing about in advance.
• Take with vitamin C (like a glass of orange juice) to enhance absorption, and avoid taking with coffee, tea, calcium supplements, or dairy.
• Every-other-day dosing has emerging research support — a study published in Blood found that alternate-day dosing improved absorption compared to daily dosing in some individuals, likely related to how the body regulates an iron-absorption hormone called hepcidin.
• Retesting after 8–12 weeks of supplementation is typical to confirm levels are improving.

Never start iron supplements without medical guidance if you haven’t been diagnosed with deficiency. Iron overload (hemochromatosis) is a real condition, and excess iron supplementation in someone who doesn’t need it can cause harm over time, including liver damage.

When Iron Deficiency Signals Something Else

In some cases — particularly in men and postmenopausal women, where heavy menstrual blood loss isn’t a factor — unexplained iron deficiency can be a sign of chronic blood loss from the gastrointestinal tract, including from ulcers, polyps, or in rarer cases, colorectal cancer. The American College of Gastroenterology recommends that unexplained iron deficiency anemia in men or postmenopausal women be evaluated with GI investigation, often including colonoscopy and/or upper endoscopy.

This isn’t meant to cause alarm — most iron deficiency has benign causes (diet, menstruation, pregnancy). But unexplained iron deficiency in someone without an obvious cause is something your doctor will want to investigate properly rather than simply treat with supplements.

Frequently Asked Questions

Final Thoughts

Iron deficiency is common, frequently overlooked, and genuinely correctable. If you’ve been feeling persistently tired, cold, foggy, or just “off” for an extended period — and especially if you fall into one of the higher-risk groups — asking your doctor for a ferritin test alongside a standard CBC is a reasonable, low-cost step.

The fix, when it’s genuinely iron deficiency, is usually straightforward: dietary changes, supplementation if needed, and addressing any underlying cause of ongoing blood loss. The improvement in energy and overall function when iron deficiency is properly corrected is often substantial.

For related reading, signs of vitamin D deficiency and benefits of magnesium cover two other widely under-recognized nutrient gaps with similarly broad effects on energy and wellbeing.

Sources:

• World Health Organization — Anaemia Fact Sheet: https://www.who.int/news-room/fact-sheets/detail/anaemia
• National Institutes of Health Office of Dietary Supplements — Iron: https://ods.od.nih.gov/factsheets/Iron-HealthProfessional/
• American College of Gastroenterology — Iron Deficiency Anemia Guidelines: https://gi.org/
• Allen LH — “Iron Supplements: Scientific Issues Concerning Efficacy and Implications.” Journal of Nutrition
• Stoffel NU et al. — “Iron Absorption from Alternate-Day Supplementation.” Blood (2020)
• Sleep Medicine Reviews — Iron Deficiency and Restless Legs Syndrome Research