How to tell if your iron deficient: Why you’re exhausted and what to do next

You’re tired. Not just "I stayed up too late watching Netflix" tired, but a heavy, bone-deep exhaustion that doesn't go away after a weekend of sleeping in. You might notice your heart doing a weird little flutter when you walk up a flight of stairs, or maybe your legs feel restless the second you hit the sheets at night. It’s easy to blame stress or age. Most people do. But if you’re trying to figure out how to tell if your iron deficient, the signs are usually hiding in plain sight, tucked away in the small details of your daily life.

Iron isn’t just some mineral on the periodic table. It’s the engine room of your blood. Specifically, it’s the key component of hemoglobin, the protein in your red blood cells that carries oxygen from your lungs to the rest of your body. Without enough of it, your tissues are basically suffocating on a cellular level. It's a slow-motion energy crisis.

The subtle red flags most people ignore

Honestly, the first symptoms are annoying rather than alarming. You might find yourself reaching for a third cup of coffee by 2:00 PM. Your skin looks a bit "off"—maybe a sallow or pale tone that people mistake for you needing a vacation. According to the Mayo Clinic, iron deficiency anemia can develop so slowly that your body actually adapts to the low oxygen levels, making you think your constant fatigue is just your "new normal."

Check your fingernails. Are they brittle? Do they curve inward like a spoon? That’s a condition called koilonychia, and it’s a classic, though later-stage, sign that your iron stores are tanking.

Then there’s the tongue thing. If your tongue looks unusually pale, smooth, or feels weirdly sore for no reason, that’s inflammation called glossitis. Your body is literally struggling to maintain its own tissues because the oxygen delivery system is failing. It sounds dramatic because it is. Oxygen is life.

The weird cravings you shouldn't ignore

Have you ever found yourself wanting to chew on ice? Not just crunching the leftovers in a soda, but actively seeking out a cup of ice to gnaw on? This is called pica. It’s a psychological and physiological phenomenon where iron-deficient people crave non-food items.

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1. Some people crave dirt or clay.
2. Others find the smell of gasoline or cleaning supplies strangely alluring.
3. Ice (pagophagia) is the most common one in the Western world.

Researchers aren't 100% sure why this happens, but some studies suggest ice chewing might increase alertness by sending more blood to the brain, helping to mask the brain fog that comes with low iron. If you’re hunting through the freezer at midnight for "the good ice," your body is screaming for help.

Why "normal" blood tests might be lying to you

This is where it gets tricky. You go to the doctor, they run a Complete Blood Count (CBC), and tell you your hemoglobin is fine. You leave feeling gaslit. But here’s the thing: how to tell if your iron deficient involves more than just checking your hemoglobin.

You need to ask for a Ferritin test.

Think of hemoglobin like the cash in your wallet, and ferritin like your savings account in the bank. You can have plenty of cash in your wallet today, but if your bank account is at zero, you’re still broke. Ferritin measures your stored iron. You can have a "normal" hemoglobin level while your ferritin is dangerously low. This is called non-anemic iron deficiency. You feel like garbage, but the standard tests say you’re "fine."

• Hemoglobin: Shows what’s circulating right now.
• Ferritin: Shows your reserves. (Aim for at least 30 ng/mL, though many functional medicine experts prefer seeing it above 50 or even 70 for optimal energy).
• Transferrin Saturation: Shows how well your blood is actually transporting the iron it has.

The unexpected culprits: Why is your iron low anyway?

It’s rarely just about not eating enough spinach. In fact, iron deficiency is often a symptom of something else. For women of childbearing age, heavy periods (menorrhagia) are the leading cause. If you’re changing a pad or tampon every hour, you’re losing blood—and iron—faster than your body can replace it.

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But what if you aren't a woman with heavy cycles?

Then we look at the gut. Conditions like Celiac disease or Crohn’s can prevent you from absorbing iron, no matter how many steaks you eat. Even a common stomach bacteria called H. pylori or the long-term use of acid blockers (PPIs) can mess with your iron levels. You need stomach acid to break down iron so it can be absorbed in the small intestine. If you’re nuking your stomach acid every day for heartburn, you might be accidentally starving your blood of iron.

Then there’s the athlete factor. Runners often suffer from "foot-strike hemolysis," where the physical impact of their feet hitting the pavement actually ruptures red blood cells. Plus, you lose iron through sweat. If you’re training hard and feeling sluggish, it’s not just "overtraining"—it’s likely a nutritional deficit.

How to actually fix it (without ruining your digestion)

If you find out you're low, don't just grab the cheapest ferrous sulfate bottle at the drugstore. That stuff is notorious for causing constipation and stomach pain. It’s basically like swallowing a handful of rusty nails.

Instead, look for Iron Bisglycinate. It’s a chelated form that is much easier on the stomach and generally better absorbed.

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• Vitamin C is your best friend. Iron needs an acidic environment to be absorbed. Take your supplement with a glass of orange juice or a Vitamin C tablet.
• Avoid the "Iron Blockers." Don't take your iron with coffee, tea, or dairy. The tannins in tea and the calcium in milk bind to iron and prevent it from entering your bloodstream. Wait at least two hours between your morning latte and your iron pill.
• Cast iron cooking. It sounds like an old wives' tale, but cooking acidic foods (like tomato sauce) in a cast-iron skillet actually leaches small amounts of dietary iron into your food. It’s not a cure-all, but every bit helps.

When to see a specialist

If you’ve tried oral supplements and your levels aren't budging, or if your ferritin is in the single digits, you might need an iron infusion. This is a common procedure where iron is delivered directly into your vein. It bypasses the gut entirely. For people with malabsorption issues, this is often a life-changing "reset."

Don't self-diagnose. Iron overload (hemochromatosis) is a real and dangerous condition where your body stores too much iron, which can damage your liver and heart. You must get blood work done before starting a high-dose regimen.

Actionable Next Steps

If you suspect you're struggling with iron levels, follow this checklist to get answers quickly:

1. Track your symptoms for one week. Note down specific instances of dizziness, heart palpitations, or "brain fog." This data is invaluable for your doctor.
2. Request a full iron panel. Do not settle for just a CBC. Specifically ask for Ferritin and Iron Saturation.
3. Check your medications. If you are on PPIs or antacids, discuss with your doctor if these are interfering with your mineral absorption.
4. Audit your diet for inhibitors. If you're eating iron-rich foods like lentils or red meat, make sure you aren't washing them down with black tea or coffee, which can cut absorption by up to 60%.
5. Look at the "Why." If you are iron deficient, work with a professional to find the source of the loss (gut issues, heavy cycles, etc.) rather than just masking it with supplements.

Iron deficiency is a slow-burn problem. It steals your personality and your drive so gradually you might not even realize you're gone. But once you address the root cause and get those levels back up, the "brain fog" clears, the exhaustion lifts, and you finally feel like yourself again.