That Exhaustion Might Not Be What You Think

You've been sleeping enough, drinking water, managing stress — and you're still dragging through the afternoon like you haven't slept in days. Before you blame burnout, consider this: iron deficiency is the most common nutritional deficiency in the world, affecting an estimated 2 billion people according to the World Health Organization.

And fatigue is its calling card.

What Iron Does in Your Body

Iron's primary job is building hemoglobin — the protein in red blood cells that carries oxygen from your lungs to every tissue in your body. About 70% of your body's iron is in hemoglobin.

But iron also:

  • Supports myoglobin, which stores oxygen in muscles
  • Is essential for energy production in mitochondria
  • Plays a role in immune function
  • Helps synthesize DNA
  • Supports cognitive function and brain development in children

Your body can't make iron. Every milligram has to come from food or supplements. And because iron is lost through bleeding, skin shedding, and sweat, you need a steady supply.

The Two Types of Dietary Iron

Heme iron comes from animal sources — red meat, poultry, and fish. It's absorbed at a rate of 15-35%. This is the efficient version.

Non-heme iron comes from plants — spinach, lentils, fortified cereals, beans. It's absorbed at a rate of only 2-20%. The body has to work harder to use it.

This absorption difference is why vegetarians and vegans need 1.8 times more iron than meat-eaters, according to the National Institutes of Health Office of Dietary Supplements.

Vitamin C dramatically improves non-heme iron absorption. A 1968 study by Monsen and colleagues demonstrated that adding 75 mg of vitamin C to a meal could boost non-heme iron absorption by up to 4-fold.

Who's Most at Risk for Deficiency

  • Menstruating women — blood loss during periods is a major drain on iron stores
  • Pregnant women — blood volume increases by about 50%, requiring significantly more iron
  • Vegetarians and vegans — reliance on lower-absorption non-heme iron
  • Endurance athletes — increased iron loss through sweat, gut bleeding from impact, and a phenomenon called "foot-strike hemolysis"
  • People with digestive conditions — celiac disease, IBD, and other conditions that impair absorption

Too Much of a Good Thing

Iron is one of the few minerals where more is definitely not better. Excess iron accumulates in organs and causes oxidative damage. Hemochromatosis, a genetic condition affecting roughly 1 in 200 people of Northern European descent, causes dangerous iron overload.

Never supplement iron without a blood test confirming deficiency. A serum ferritin test measures your iron stores — levels below 30 ng/mL suggest depletion, while levels above 200 ng/mL (men) or 150 ng/mL (women) may indicate overload.

When to See a Professional

Persistent fatigue, pale skin, brittle nails, frequent infections, restless legs, or unusual cravings for ice or dirt (pica) are all potential signs of iron deficiency. A simple blood panel — including ferritin, serum iron, and total iron-binding capacity (TIBC) — can tell you exactly where you stand.

The Bottom Line

Iron is essential for oxygen transport, energy production, and immune function. Deficiency is common and often overlooked — especially in women, vegetarians, and athletes. Get tested before supplementing, pair plant-based iron with vitamin C, and don't dismiss unexplained fatigue without checking your levels.

FAQ

What foods are highest in iron? Oysters, red meat, liver, and dark-meat poultry are top heme iron sources. For non-heme: fortified cereals, lentils, white beans, spinach, and tofu. Cooking in cast iron pans can also add small amounts of iron to food.

Can you take too much iron? Yes, and it's dangerous. Iron overload causes liver damage, joint pain, and heart problems. This is why iron supplements should only be taken when deficiency is confirmed by blood work.

Why do iron supplements cause constipation? Iron irritates the digestive tract and slows gut motility. Taking iron with food (though this reduces absorption) or choosing iron bisglycinate (a gentler form) can help. Your doctor may also recommend staggering doses or taking iron every other day, which a 2017 study in The Lancet Haematology found was actually more effective for absorption.

A note from Living & Health: We're a lifestyle and wellness magazine, not a doctor's office. The information here is for general education and entertainment — not medical advice. Always talk to a qualified healthcare professional before making changes to your health routine, especially if you have existing conditions or take medications.