Should You Take Iron Supplements for Heavy Periods? Test First

If you have heavy periods, ask your GP for a ferritin and full blood count before you buy iron tablets: heavy menstrual bleeding is the commonest cause of iron deficiency in women, so a test is very likely to be worth having, and iron supplements help only when you are actually short. Around two-thirds of women with heavy periods are iron deficient and many have iron deficiency anaemia, often without realising that their tiredness, breathlessness and hair shedding have a cause.¹ Taken when you are not short, iron does nothing useful and brings constipation and nausea. Taken when you are, it works slowly, over months, and works better on alternate days than every day.² The other half of the answer is the bleeding itself, which a GP can reduce; replacing iron you keep losing is a treadmill.

• First step: a ferritin test; below 30 micrograms per litre is iron deficiency in UK guidance, even with a normal haemoglobin
• What a heavy period costs: about 0.5 mg of iron per millilitre of blood, so a heavy period of 80 ml or more loses 40 mg plus, against a daily intake of 14.8 mg of which about 15% is absorbed
• If you are short: iron on alternate days, with vitamin C food, away from tea, coffee, dairy and calcium; expect three to six months
• If you are not: iron-rich food, and a repeat test if symptoms persist
• Reduce the bleeding: tranexamic acid, the hormonal coil, the pill and other options are a GP conversation

How much iron do you lose in a heavy period?

Blood contains about 0.5 mg of iron per millilitre. An average period loses 30 to 40 ml of blood over its course, about 15 to 20 mg of iron, which a normal diet replaces. A heavy period is defined clinically as more than 80 ml, which costs 40 mg of iron or more each month, and many women with heavy bleeding lose far more than that.^{1, 3} Set that against the UK reference intake for women aged 19 to 50 of 14.8 mg a day, of which the body absorbs roughly 15% from a mixed diet, and the arithmetic is clear: a heavy period can remove more iron in a week than food can replace in a month, which is why deficiency builds over a year or two and why the old version of this page, which called 30 to 40 mg the "average" loss, understated the problem.

Signs you may be low in iron

Tiredness out of proportion to your life, breathlessness on stairs, a racing heart, pale skin and inner eyelids, feeling cold, headaches, poor concentration, brittle nails and hair shedding, restless legs, and a craving to chew ice. All overlap with B12 deficiency and thyroid problems, which is why a test beats a symptom list.³ Our page on B12 for women explains how the two deficiencies hide behind each other.

What test to ask for, and what the number means

A full blood count, which shows haemoglobin and whether you are anaemic, and a serum ferritin, which measures iron stores. UK guidance treats a ferritin below 30 micrograms per litre as iron deficiency; below 15 is unequivocal.^{3, 4} The point most women miss, and some GPs too, is that you can be iron deficient with a normal haemoglobin: stores run down first, and symptoms begin while the blood count still reads "normal". A ferritin of 12 with a haemoglobin of 125 is a deficiency that deserves treating. Ferritin also rises with inflammation or infection, so a result taken while you are ill can look falsely reassuring; ask for a repeat if that applies. Forum talk of needing a ferritin "over 70 for hair" or "over 100 to feel well" goes beyond the evidence; the clinical threshold is 30, and how you feel after correcting it is the test.

If you are low: how to take iron so it works

Alternate days, not daily. Absorption studies show that a dose of iron raises hepcidin, the hormone that shuts the gut's iron gate, for about 24 hours, so a tablet taken the next day is largely wasted. Taking the same total on alternate days absorbs more iron and causes fewer side effects, and a randomised trial in iron-depleted women confirmed it.^{2, 5}

Know the elemental dose. Labels state the compound; the iron inside it is what counts. A 200 mg ferrous sulphate tablet is 65 mg of iron; 210 mg ferrous fumarate is 69 mg; 300 mg ferrous gluconate is 35 mg; a 14 mg "gentle" tablet or a liquid sachet is 5 to 14 mg. A GP-prescribed dose for deficiency is around 65 mg of elemental iron on alternate days; an over-the-counter 14 mg product tops up a diet but will not correct a deficiency in any reasonable time. Our guide to iron supplement side effects goes through the forms.

Timing and company. An hour before food or two hours after, with water or orange juice; if that upsets your stomach, with a small meal that is not dairy. Keep tea and coffee an hour away, because their polyphenols block absorption, and separate iron from calcium supplements, antacids, levothyroxine and some antibiotics by two to four hours. Vitamin C in the same meal helps non-haem iron absorption in single-meal studies; a trial adding vitamin C tablets to iron found no extra benefit, so a glass of juice is reasonable and a 1,000 mg vitamin C tablet is not needed.⁶

Expect months, and retest. Haemoglobin recovers over four to eight weeks; ferritin, the store, takes three to six months to rebuild, and the usual advice is to continue three months beyond a normal haemoglobin. Energy often improves before the numbers do. Black stools are normal; severe constipation means the dose or form needs changing, not stopping.

If you are not low

Iron supplements will not give you energy and the excess is not harmlessly excreted; iron is one of the few nutrients the body cannot easily get rid of, and the UK guidance level for supplements is 17 mg a day for people without deficiency. Eat for iron instead: red meat once or twice a week if you eat it, sardines and mackerel, eggs, lentils and chickpeas, tofu, fortified cereals, dried apricots and dark green vegetables, with vitamin C alongside and tea away from meals. Foods high in iron has the UK portions. Retest in six months if heavy periods continue and symptoms persist.

Treat the bleeding, not only the iron

This is the part most iron advice leaves out. NHS guidance on heavy menstrual bleeding offers tranexamic acid tablets taken during the period, the hormonal coil, the combined pill or other hormonal options, and investigation for fibroids, polyps, adenomyosis or thyroid problems where the pattern suggests them.¹ Which, if any, suits you is a conversation with your GP, and iron deficiency is one of the reasons to have it; replacing iron you keep losing month after month is not a long-term plan. Any bleeding between periods, after sex or after the menopause needs a GP appointment on its own account.

What we don't know

• The ferritin level at which symptoms start in women with normal haemoglobin. Thresholds are set on evidence of deficiency, not on how people feel.⁴
• Whether low-dose daily iron matches alternate-day higher dose for mild deficiency. Both work; comparative data are limited.²

Frequently asked questions

Should I take iron tablets if I have heavy periods?

Only after a ferritin test shows you are short, which is likely with heavy bleeding. Iron taken when you are not short does nothing but cause side effects.^{1, 3}

How much iron do you lose during a heavy period?

About 0.5 mg per millilitre of blood, so a heavy period of 80 ml or more loses 40 mg of iron, roughly what a month of normal eating absorbs.¹

What are the signs iron tablets are working?

More energy and less breathlessness within a few weeks, then a rising haemoglobin at four to eight weeks and a rising ferritin over months. Black stools are expected.

How long does it take to raise iron levels?

Haemoglobin four to eight weeks; ferritin three to six months, continuing three months after the blood count is normal.³

Is there an alternative to iron tablets for anaemia?

Alternate-day dosing or a different iron salt if side effects are the problem, an iron infusion through the GP or hospital if tablets fail, and treating the bleeding. Food alone cannot correct an established deficiency quickly.

Sources

1. Munro MG, et al. The relationship between heavy menstrual bleeding, iron deficiency, and iron deficiency anemia. American Journal of Obstetrics and Gynecology, 2023. PubMed 36706856.
2. Stoffel NU, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women. Lancet Haematology, 2017. PubMed 29032957.
3. Lopez A, et al. Iron deficiency anaemia. Lancet, 2016. PubMed 26314490.
4. Snook J, et al. British Society of Gastroenterology guidelines for the management of iron deficiency anaemia in adults. Gut, 2021. PubMed 34497146.
5. von Siebenthal HK, et al. Alternate day versus consecutive day oral iron supplementation in iron-depleted women: a randomized double-blind placebo-controlled study. EClinicalMedicine, 2023. PubMed 38021373.
6. Li N, et al. The efficacy and safety of vitamin C for iron supplementation in adult patients with iron deficiency anemia: a randomized clinical trial. JAMA Network Open, 2020. PubMed 33136134.

This article is general information, not medical advice. Heavy periods, symptoms of anaemia, or bleeding between periods, after sex or after the menopause need a GP appointment; do not take iron for a suspected deficiency without a blood test.