Iron Deficiency in Women: Why It's So Common and What the Tests Often Miss

You've been tired for months. Not the kind of tired that goes away after a good night's sleep. The kind that sits in your chest, makes everything feel slightly harder than it should, and leaves you searching the internet at midnight for what might be wrong. Maybe you've also noticed more hair than usual coming out in the shower. Maybe you get dizzy when you stand up too fast, or your hands are cold when everyone else in the room is fine.

You go to the doctor. They do a blood test. The result comes back normal.

And then what? You go home, still tired, with no explanation. This happens more often than it should, and there is a specific reason it happens. But let's start at the beginning.

What iron deficiency actually is, and how it differs from anaemia

Iron deficiency and iron deficiency anaemia are not the same thing, even though people often use the terms interchangeably. Iron deficiency anaemia is what happens when your iron stores have been depleted for long enough that your haemoglobin levels drop below the normal range. Haemoglobin is the protein in red blood cells that carries oxygen around your body. When there is not enough iron to make it, things start to go wrong.

Iron deficiency, on the other hand, can exist before anaemia sets in. Your haemoglobin might still be in the normal range, but your ferritin, which is the protein that stores iron, is already running low. You can feel actually unwell at this stage. The fatigue is real. The hair loss is real. The difficulty concentrating is real. But a haemoglobin test will not catch it.

This is the gap that often goes unaddressed.

How common this actually is

Very. According to the World Health Organization, in 2019 approximately 30% of non-pregnant women and 37% of pregnant women between the ages of 15 and 49 worldwide were affected by anaemia. In numbers, that is 539 million non-pregnant women and 32 million pregnant women. And iron deficiency is the most common nutritional cause of anaemia globally.

The WHO identifies menstruating adolescent girls and women, as well as pregnant and postpartum women, as the groups most vulnerable. This is not a rare condition. It is one of the most common health issues affecting women of reproductive age, and it is still frequently missed.

Why menstruating women are at particular risk

Every month, blood loss takes iron with it. If dietary iron intake does not replace what is lost, stores gradually run down. This is not always dramatic or obvious. It can happen slowly over months or years, especially if periods are heavy.

According to the National Heart, Lung, and Blood Institute (NIH), heavy menstrual periods are one of the primary causes of iron deficiency anaemia in women. Other contributors include conditions that affect iron absorption, such as coeliac disease, Crohn's disease, and ulcerative colitis. Interestingly, endurance sports are also on the list, because intense physical training can cause iron losses through the gastrointestinal tract and through the breakdown of red blood cells. So if you are both menstruating and training regularly, your risk is higher than either factor alone.

The symptoms, including the ones that often get missed

The well-known symptoms of iron deficiency anaemia include fatigue, dizziness or lightheadedness, cold hands and feet, pale skin, shortness of breath, and headaches. Both the WHO and the NHLBI list these as the core presentation. Worth noting: the NIH also points out that people with mild or moderate iron deficiency anaemia may have no symptoms at all, which is one of the reasons it can quietly persist for a long time before anyone investigates.

The symptoms that tend to come up less often in standard explanations include hair thinning and shedding, difficulty concentrating, restless legs at night, and a general sense of running at 60% when you should be at 100%. These are the symptoms that show up before haemoglobin drops, when ferritin is low but the standard blood test still shows "normal."

The test that often gets skipped

Here is the practical part. When you ask your doctor to check your iron levels, what is usually measured is haemoglobin, sometimes alongside a full blood count. This will identify iron deficiency anaemia, but only once it has progressed to the point where haemoglobin is actually affected.

Ferritin, the marker for iron storage, is a separate test. It is not automatically included in standard blood panels in many healthcare systems. If you have the symptoms described above and your haemoglobin comes back normal, it is worth asking your doctor specifically whether your ferritin has been checked. Not demanding or self-diagnosing. Just asking whether it was included.

Ferritin reference ranges vary between laboratories, so whether your result counts as "low" or "optimal" depends on the lab and the clinical context. This is a conversation to have with your doctor rather than a number to interpret alone.

What to eat, and what matters about how you eat it

Iron from food comes in two forms. Haem iron, found in animal products, is more easily absorbed by the body. Non-haem iron, found in plant-based foods, is still useful but absorbed less efficiently. According to the NHLBI, good sources of iron include beans, dried fruits, eggs, lean red meat, salmon, iron-fortified breads and cereals, peas, tofu, and dark green leafy vegetables.

Vitamin C clearly improves non-haem iron absorption. Eating an orange alongside your lentil soup, or having strawberries with your iron-fortified cereal, is a simple and effective combination. The NHLBI specifically recommends pairing vitamin C-rich foods with iron sources for this reason.

A few things work against iron absorption and are worth knowing about. Calcium competes with iron for absorption, so having a large glass of milk alongside an iron-rich meal is not ideal. Tannins, found in tea and coffee, also inhibit absorption. This does not mean you need to give them up, but having your tea or coffee an hour or so before or after an iron-rich meal is a reasonable adjustment if you are actively trying to rebuild stores.

About supplementation

If your ferritin or haemoglobin levels are actually low, dietary adjustments alone may not be enough to bring them back up in a reasonable timeframe. Iron supplements can help, but they come with a common side effect: constipation and gastrointestinal discomfort. If this is an issue, iron bisglycinate is a form that many people find gentler on the stomach, though you should discuss this with your GP or pharmacist rather than switching supplements on your own.

The time it takes to see improvement varies. It is generally measured in weeks to months, not days. Building ferritin back up after it has been depleted takes time even when treatment is going well.

Frequently asked questions

How do I know if it's iron deficiency and not something else causing my fatigue?

You don't, based on symptoms alone. Fatigue has many causes: thyroid issues, vitamin B12 deficiency, vitamin D, sleep problems, depression. Iron deficiency is one item on a longer list. A blood test is the only way to know. If you are persistently tired without explanation, that is reason enough to ask for bloodwork, including ferritin.

Can I fix iron deficiency with diet alone?

For mild cases, possibly. For more significant deficiency, especially if you are losing iron monthly through periods, diet usually needs to be supplemented while the cause of the deficit is addressed. Your doctor can advise based on your actual levels.

How long does it take for iron levels to come back up?

If taking supplements, haemoglobin levels generally begin to improve within a few weeks, but ferritin rebuilds more slowly, often over several months of consistent supplementation and dietary support. Retesting after three to six months is typical.

Is hair loss from iron deficiency reversible?

Iron deficiency is one possible cause of increased hair shedding, but not the only one. When it is the cause, hair usually recovers once iron stores are restored, though this can take time. If hair loss is a concern, it is worth mentioning to your doctor alongside requesting the iron and ferritin test.

Do I need to worry about this if I'm postmenopausal?

After menopause, monthly blood loss is no longer a factor, which reduces the risk. However, iron deficiency can still occur for other reasons, including absorption problems or GI blood loss. If you have symptoms, it is still worth checking.

The honest takeaway

Iron deficiency is extremely common in women of reproductive age, well-documented by the WHO and NIH, and still regularly under-investigated. The symptoms can be vague enough to get written off or attributed to something else. And the standard blood test does not always tell the whole story.

The practical step, if any of this resonates, is to go to your doctor and ask specifically whether both haemoglobin and ferritin were checked. That is not a dramatic move. It is the kind of conversation that should be routine but often is not.

Have you had your ferritin checked, or found that standard tests kept coming back normal while you still felt unwell? It is a more common experience than most people realise.

This article is for general information only and is not a substitute for advice from a qualified medical professional. If you have concerns about your iron levels or health, please speak to your doctor.

• Nutrition
• Women's Health
• anaemia
• fatigue
• ferritin
• iron deficiency