Iron Deficiency in Women: The Most Overlooked Cause of Fatigue

You're exhausted. Not the kind of tired that sleep fixes — the deep, bone-level fatigue where you wake up feeling like you never went to bed. You mention it to your doctor. They check your thyroid. It's normal. They suggest you're stressed, or depressed, or not sleeping well. They might even tell you it's just part of being a busy woman.

Meanwhile, nobody checked your ferritin.

The Scope of the Problem

Iron deficiency is the most common nutritional deficiency worldwide, and women of reproductive age are disproportionately affected. In the U.S., roughly 10% of women are iron deficient, and among those with heavy menstrual bleeding, the number climbs to 20-30%.

Here's what makes this especially frustrating: iron deficiency causes symptoms long before it shows up as anemia on a standard blood count. You can have a perfectly normal hemoglobin and still be profoundly iron depleted — and profoundly symptomatic.

Why Women Are Vulnerable

The math is straightforward. Women lose iron through menstruation every month. The average menstrual blood loss translates to about 1 mg of iron per day during a period. Add in the fact that dietary iron absorption is inherently limited (you absorb only 10-20% of what you eat), and many women are running a chronic iron deficit.

Contributing factors:

• Heavy periods (menorrhagia). If you're soaking through pads/tampons every 1-2 hours or passing clots, your iron losses are significantly above average.
• Pregnancy and breastfeeding. Iron demands increase dramatically — a singleton pregnancy requires roughly 1,000 mg of additional iron.
• Vegetarian or vegan diets. Non-heme iron (plant sources) is absorbed at roughly 2-5%, compared to 15-35% for heme iron (meat sources).
• GI conditions. Celiac disease, inflammatory bowel disease, and chronic PPI use can all impair iron absorption.
• Frequent blood donation. Each donation removes approximately 250 mg of iron.

Symptoms Beyond Fatigue

Iron deficiency affects virtually every organ system. Beyond fatigue, watch for:

• Exercise intolerance. Your cardio endurance tanks because iron is essential for oxygen transport to muscles. Workouts that used to feel manageable now feel impossible.
• Brain fog and poor concentration. Iron is involved in neurotransmitter synthesis and neuronal energy metabolism. Cognitive function suffers early.
• Hair loss. Iron deficiency is one of the most common reversible causes of telogen effluvium (diffuse hair shedding). Your ferritin doesn't need to be zero — levels below 30-40 are associated with increased shedding.
• Restless legs. That irresistible urge to move your legs at night is strongly associated with low iron stores, particularly when ferritin is below 50.
• Pica and pagophagia. Craving ice, dirt, or starch? This is a classic (and often missed) sign of iron deficiency.
• Brittle nails, pale skin, cold hands and feet. All reflect impaired oxygen delivery and tissue iron depletion.
• Anxiety and irritability. Iron's role in dopamine and serotonin synthesis means deficiency can mimic or worsen mood disorders.

The Lab Work That Matters

Here's where many providers drop the ball. A standard CBC (complete blood count) checks hemoglobin and hematocrit — these only become abnormal once you've progressed to full iron deficiency anemia. That's the late stage.

The test you need is ferritin.

Ferritin reflects your body's iron storage. But here's the catch: most lab reference ranges list the lower limit of normal as 10-12 ng/mL. That's the threshold for avoiding severe anemia, not for feeling well.

Optimal ferritin for symptom resolution is generally 50-100 ng/mL or higher. A ferritin of 15 is technically "normal" by lab standards but functionally depleted.

Additional useful labs:

• Iron and TIBC (total iron-binding capacity). A low iron with high TIBC confirms iron deficiency.
• Transferrin saturation. Below 20% suggests insufficient iron supply to tissues.
• Reticulocyte count. Helpful for confirming your marrow is responding to treatment.

One caveat: ferritin is also an acute-phase reactant, meaning it can be falsely elevated by inflammation, infection, or liver disease. If your CRP or ESR is elevated, the ferritin number may not accurately reflect your iron stores.

Treatment: Getting Your Levels Back Up

Oral iron supplementation is first-line for most women. But not all iron supplements are equal:

• Ferrous sulfate (325 mg, containing 65 mg elemental iron) is the classic formulation. It's cheap, effective, and frequently causes GI side effects — nausea, constipation, dark stools. Take it on an empty stomach with vitamin C to maximize absorption.

• Ferrous bisglycinate is gentler on the stomach and has comparable absorption. It's a good alternative if ferrous sulfate is intolerable.

• Every-other-day dosing is now supported by research. Your body upregulates hepcidin (an iron-absorption blocker) after each dose, so taking iron every other day actually results in better fractional absorption with fewer side effects.

• Avoid taking iron with coffee, tea, calcium, or antacids. All of these significantly reduce absorption.

Expect it to take 3-6 months of consistent supplementation to meaningfully replete your stores. Check ferritin at 3 months to assess response.

IV iron is appropriate when oral supplementation fails, isn't tolerated, or when deficiency is severe. Formulations like ferric carboxymaltose (Injectafer) can replete stores in 1-2 infusions. It works faster and bypasses the GI tract entirely.

When to Dig Deeper

Iron deficiency in a premenopausal woman with heavy periods has an obvious explanation. But iron deficiency in a postmenopausal woman — or in anyone whose deficiency doesn't respond to supplementation — warrants further investigation.

Consider:

• GI blood loss. Occult bleeding from ulcers, polyps, or colon cancer. Postmenopausal women with unexplained iron deficiency should generally get a GI evaluation.
• Celiac disease. Screen with tissue transglutaminase antibodies. Celiac can present with iron deficiency as the only symptom.
• Chronic kidney disease. Impairs erythropoietin production and iron utilization.
• Menstrual evaluation. If heavy periods are the cause, treating the underlying menstrual issue (hormonal management, IUD, etc.) is essential — supplementing iron without addressing ongoing losses is futile.

The Bottom Line

Iron deficiency is common, symptomatic, and fixable — yet it's routinely missed because providers rely on hemoglobin alone and use outdated "normal" ranges for ferritin. If you're a woman with unexplained fatigue, hair loss, brain fog, or exercise intolerance, getting a proper iron panel is one of the highest-yield things you can do.

Don't accept "your labs are normal" without seeing the numbers yourself. A ferritin of 12 is not fine, regardless of what the reference range says.

Need a provider who will actually look at your iron levels? [Book with CORAL](https://coral.clinic) for a thorough evaluation.