Fatigue is one of the most common reasons women see a clinician, and one of the easiest complaints to under-investigate. Sleep, stress, and depression get the first look. Iron often does not, which is a problem, because iron deficiency, with or without anemia, is unusually common in menstruating women and produces symptoms that are easy to dismiss.
The distinction between iron deficiency and iron deficiency anemia matters. You can have depleted iron stores, and feel it, long before your hemoglobin drops enough to register as anemia on a routine blood count.
Why women are disproportionately affected
Menstruation is a monthly iron loss. Heavy menstrual bleeding, defined loosely as needing to change protection every hour or two, passing large clots, or bleeding longer than seven days, is common and often normalized. Pregnancy roughly doubles iron requirements. Vegetarian and vegan diets, while healthful in many respects, provide iron in a less bioavailable form than heme iron from animal sources. Gastrointestinal conditions such as celiac disease and inflammatory bowel disease can quietly impair absorption.
Stacked together, these factors mean that a large share of premenopausal women live with lower iron stores than optimal, whether or not their standard bloodwork looks normal.
Symptoms beyond feeling tired
Fatigue is the headline, but iron deficiency has a broader footprint.
- Exercise intolerance and unusually high perceived effort
- Shortness of breath on climbs or stairs that were previously easy
- Hair thinning or shedding beyond seasonal norms
- Brittle or spooning nails
- Restless legs, particularly at night
- Pica, a craving for ice, clay, or other non-food substances
- Cold intolerance, dizziness on standing, or difficulty concentrating
Many of these overlap with thyroid disease, depression, or perimenopause, which is precisely why iron studies belong in the workup rather than as an afterthought.
What to actually test, and how to read it
A routine complete blood count can miss early iron deficiency. Hemoglobin and mean corpuscular volume often stay in range until stores are substantially depleted. The single most useful test is ferritin, which reflects iron storage.
- A ferritin under about 15 to 30 ng/mL is generally considered deficient.
- Many clinicians, particularly those who treat athletes or women with unexplained fatigue, use higher functional thresholds, often in the 30 to 50 ng/mL range, before considering stores adequate.
- Ferritin rises with inflammation, so it should be interpreted alongside a marker like C-reactive protein when possible.
Asking specifically for a ferritin level, not just a CBC, is often the difference between a diagnosis and another shrug.
If your primary complaint is fatigue and no one has checked your ferritin, that is a gap worth filling.
Repletion, done properly
Oral iron works for most people, but the details matter. Standard dosing regimens can be poorly tolerated, and recent evidence suggests that alternate-day dosing may improve absorption and reduce gastrointestinal side effects. Taking iron with vitamin C aids uptake. Coffee, tea, calcium supplements, and antacids blunt it.
Options to discuss with a clinician:
- Oral iron every other day, often at doses around 60 to 120 mg of elemental iron
- Different iron salts if one is not tolerated
- Intravenous iron for severe deficiency, malabsorption, ongoing heavy blood loss, or oral intolerance
Repletion is slow. Ferritin typically takes months to rebuild, and stopping too early is a common reason for recurrence. Retesting after a defined interval, often three to six months, is part of doing it properly.
The bottom line
Iron deficiency is a common, treatable cause of fatigue in women, and it is routinely missed because standard blood counts do not catch it early. If you are exhausted, thinning, breathless on stairs, or craving ice, ask for a ferritin level and interpret it in context. Address the underlying source, whether menstrual, dietary, or absorptive, alongside repletion. The energy you get back can be considerable.