Iron Deficiency and Heavy Periods: The Link Your Doctor Might Be Missing

If you have been feeling exhausted, struggling to concentrate, or noticing that your hair is thinning, you might have put it down to a busy lifestyle or simply getting older. But in my experience as a gynaecologist, one of the most under-recognised causes of these symptoms in women is iron deficiency – and it is almost always linked to heavy menstrual bleeding. What concerns me is how often this connection is missed, even by healthcare professionals.

Iron deficiency is the most common nutritional deficiency worldwide, and women of reproductive age are disproportionately affected. Yet many of my patients arrive in my consulting room having been told their blood tests are “normal” – when in fact, their iron stores are critically low. I want to explain why this happens, what to look out for, and what can be done about it.

How common is iron deficiency in women?

The numbers are striking. It is estimated that around one in three women of reproductive age in the UK has low iron stores, and heavy menstrual bleeding is the leading cause. Every month, women lose iron through menstruation, and if your periods are heavy, your body simply cannot keep up with demand through diet alone.

What makes this particularly frustrating is that iron deficiency exists on a spectrum. You can be significantly iron depleted – with real, debilitating symptoms – without being technically anaemic. This means that a standard full blood count may come back as “normal”, and you are sent home with no explanation for why you feel so dreadful. I see this pattern repeatedly, and it is something I feel strongly about changing.

Recognising the symptoms of iron deficiency

Iron is essential for producing haemoglobin, which carries oxygen in your blood, but it also plays a vital role in energy production, brain function, and immune health. When your iron stores are low, the effects can be widespread and surprisingly varied:

• Persistent fatigue and exhaustion that is not relieved by rest
• Brain fog and difficulty concentrating – many women describe feeling like they are thinking through treacle
• Hair thinning and hair loss – this is one of the most common reasons women present to their GP
• Breathlessness on exertion, such as climbing stairs or exercising
• Restless legs syndrome – an uncomfortable urge to move your legs, particularly at night
• Heart palpitations and dizziness
• Pale skin, brittle nails, and mouth ulcers
• Low mood and anxiety – iron deficiency can significantly affect your mental health

Many of these symptoms overlap with other conditions, including thyroid disorders, depression, and perimenopause. This is precisely why iron deficiency so often goes undiagnosed – the symptoms are attributed to something else entirely.

What counts as heavy periods?

This is a question I am asked frequently, because many women have normalised their bleeding pattern, particularly if their mother or sisters experienced similar periods. Clinically, heavy menstrual bleeding (menorrhagia) is defined as blood loss of more than 80 ml per cycle, but in practice, the most useful measure is how your periods affect your daily life.

You may have heavy periods if you experience:

• Needing to change your pad or tampon every one to two hours
• Passing blood clots larger than a 10p coin
• Bleeding through to your clothes or bedding (flooding)
• Needing to use double protection (pad and tampon together)
• Periods lasting longer than seven days
• Avoiding activities or missing work because of your period

If any of this resonates with you, your bleeding is not something you should simply endure. Heavy periods deserve investigation, both to identify the underlying cause and to address the iron deficiency that almost inevitably follows.

Why ferritin matters more than haemoglobin

This is perhaps the most important message I can share. When your GP checks for iron deficiency, they typically request a full blood count, which measures your haemoglobin level. If your haemoglobin is within the reference range, you may be told everything is fine. But haemoglobin is the last thing to drop when your iron stores are depleting – it is a late marker.

The test that truly reflects your iron stores is serum ferritin. Ferritin is the protein that stores iron in your body, and it depletes long before your haemoglobin falls. A ferritin level below 30 µg/L is associated with symptoms such as fatigue, hair loss, and cognitive difficulties, even if your haemoglobin is perfectly normal.

I routinely aim for my patients to have a ferritin level of at least 50 µg/L, and ideally above 70 µg/L, particularly if they are symptomatic. Many laboratories report ferritin as “normal” at levels as low as 13 µg/L, which in my view is far too low for optimal wellbeing. If you have been told your iron levels are normal but you still feel unwell, I would strongly encourage you to ask for your actual ferritin number.

Treating iron deficiency: oral supplements

Once iron deficiency is confirmed, the first line of treatment is usually oral iron supplementation. However, not all iron supplements are created equal, and how you take them matters enormously for absorption.

The most commonly prescribed form is ferrous sulphate (200 mg tablets), but many women find this causes significant gastrointestinal side effects, including nausea, constipation, and stomach cramps. If this is the case for you, there are alternatives:

• Ferrous fumarate or ferrous gluconate may be better tolerated
• Iron bisglycinate (available over the counter) is gentler on the stomach and well absorbed
• Liquid iron preparations can be easier to tolerate and allow flexible dosing

To maximise absorption, I advise my patients to:

• Take iron on an empty stomach if tolerated, or with a small amount of food if not
• Take it with vitamin C (a glass of orange juice or a vitamin C tablet) to enhance absorption
• Avoid taking iron at the same time as tea, coffee, dairy, or calcium supplements, as these inhibit absorption
• Consider taking iron every other day rather than daily – recent research suggests this may actually improve absorption and reduce side effects

It typically takes three to six months of consistent supplementation to replenish iron stores, and I recommend rechecking ferritin levels after three months to assess progress.

When intravenous iron is needed

For some women, oral iron is simply not enough. If you cannot tolerate oral supplements, if your ferritin remains stubbornly low despite months of treatment, or if your iron deficiency is severe, intravenous (IV) iron infusion may be the most effective option.

IV iron bypasses the gut entirely, delivering iron directly into your bloodstream. Modern IV iron preparations, such as ferric carboxymaltose (Ferinject) or iron isomaltoside (Monofer), are safe and can be administered in a single session lasting 15 to 30 minutes. Most women notice a significant improvement in their energy levels within one to two weeks.

I arrange IV iron infusions for my patients when it is clinically indicated, and I find it can be truly transformative – particularly for women who have been struggling with fatigue for months or years.

Treating the underlying cause

Replacing iron is essential, but it is equally important to identify and treat why your periods are heavy in the first place. Iron supplementation alone is like bailing water out of a boat without fixing the leak. The most common causes of heavy menstrual bleeding include:

• Uterine fibroids – benign growths in the womb that can cause heavy, prolonged bleeding
• Adenomyosis – a condition where the lining of the womb grows into the muscular wall, often causing painful, heavy periods
• Hormonal imbalance – including anovulatory cycles, which are common in the years approaching perimenopause
• Endometrial polyps – small growths on the lining of the womb
• Coagulation disorders – bleeding conditions such as von Willebrand disease, which are more common in women than often appreciated

An appropriate assessment typically includes a detailed history, pelvic examination, pelvic ultrasound, and blood tests. Depending on the cause, treatment options range from hormonal management (such as the Mirena coil, combined pill, or tranexamic acid) to surgical interventions including polyp removal, fibroid treatment, or endometrial ablation.

The key point is this: heavy periods are not something you have to accept as normal. There is almost always something that can be done, both to reduce your bleeding and to restore your iron levels.