Heavy periods and iron deficiency: when is bleeding too much?
Short answer: on average you lose about 30 to 40 millilitres of blood per period, roughly two to three tablespoons. From around 80 ml per cycle, doctors call it heavy menstrual bleeding. Heavy periods are one of the leading causes of iron deficiency in people of reproductive age worldwide.
Almost nobody measures their blood loss in millilitres. That's why clinicians look at practical signals instead, and you can spot those yourself.
When is a period too heavy?
- You need to change a tampon, pad or empty a cup every one to two hours.
- You double up on protection to avoid leaking through.
- You pass clots larger than a 2.5 cm coin.
- You bleed for more than seven days.
- You get up at night to change protection.
- You plan your work, sport or social life around your bleeding.
That last point may matter most. If your period runs your life, "it's probably fine" isn't a useful benchmark.
Why heavy periods cause iron deficiency
Blood contains iron. If you consistently lose more than you replace through food, your iron stores shrink. This happens in stages: first your storage iron (ferritin) drops, then haemoglobin falls and you have iron deficiency anaemia.
The catch: low ferritin without anaemia can already cause symptoms while a standard haemoglobin test still looks normal. Ask your doctor explicitly about ferritin, not just Hb.
Signs of iron deficiency
- Fatigue that sleep doesn't fix
- Breathlessness or a racing heart on exertion
- Pale skin, gums or inner eyelids
- Hair shedding and brittle nails
- Dizziness, headaches, poor concentration
- Cold hands and feet
- Restless legs at night
- Sometimes: craving ice or non-food items (pica)
Sound familiar? Also read why you're so tired during your period.
What causes heavy bleeding?
Heavy bleeding is a symptom, not a diagnosis. Common causes include fibroids, polyps, endometriosis and adenomyosis, a copper IUD, thyroid problems, bleeding disorders such as von Willebrand disease (often diagnosed late), medications like blood thinners, and the perimenopausal years when cycles get erratic.
What you can do
1. Track it. Log daily flow, how often you change protection and whether there are clots. Two or three cycles of data is far more useful to a doctor than "it's quite a lot". PERIOD. lets you log flow and symptoms per day, without selling that data.
2. Eat iron smartly. Haem iron from animal products is absorbed more easily than non-haem iron from legumes, tofu, wholegrains, nuts and dark leafy greens. Vitamin C markedly boosts non-haem absorption, so add peppers, citrus or kiwi to the meal. Coffee and tea with meals reduce absorption, better an hour before or after.
3. Don't self-prescribe iron tablets. Too much iron isn't harmless, and your symptoms may have another cause. Get tested first.
When to see a doctor
Book an appointment if you leak through maximum protection, bleed longer than seven days, pass large clots, bleed between periods, notice a sudden increase in flow, or have fatigue symptoms. Treatments exist, from tranexamic acid and hormonal options to treating the underlying cause.
This article is general information, not medical advice.
FAQ
How much blood is normal in a period?
On average 30–40 ml across the whole period. Above 80 ml per cycle counts as heavy.
Are clots normal?
Small clots are normal on heavy days. Frequent clots bigger than about 2.5 cm are worth checking.
Can heavy periods cause anaemia?
Yes, chronic heavy bleeding is among the most common causes of iron deficiency anaemia in menstruating people.
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