Heavy Periods in Perimenopause are Draining Your Iron
You're tired in a way that sleep doesn't seem to fix. There's brain fog in the mornings, and more hair than usual in the shower drain. So you asked your doctor for bloodwork, hoping it would finally explain something. It came back normal. Nothing wrong. Which means the tiredness must just be stress, or your age, or being a woman, take your pick.
One thing didn't come up: your periods. Over the past few months they've gotten heavier, longer, and closer together. Iron deficiency in perimenopause is one of the biggest reasons you can feel exactly like this and still get told you're fine, and while you're still menstruating, the cause is usually the bleeding itself. It's easy to miss when everyone's focused on a lab result.
Iron deficiency in perimenopause is usually caused by heavy menstrual bleeding rather than by the hormone shift itself. As ovulation becomes less regular, progesterone falls, the uterine lining builds up, and periods get heavier and less predictable. The blood loss outpaces what the body absorbs from food, and ferritin drops well before hemoglobin does.
How Much Iron Your Period Takes Each Month
Heavy menstrual bleeding is the most common cause of iron deficiency in women who still have periods. Every cycle you lose blood, and blood carries iron. An average period sheds around 30 to 60 mL of blood, roughly 25 mg of iron, about the same as ten beef burgers. A heavy one can reach sixteen burgers, and your body only rebuilds it slowly, through food and absorption.
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Put plainly, each millilitre of blood carries roughly 0.5 mg of iron, and a typical cycle sheds 30 to 60 mL, so somewhere between 15 and 30 mg of iron leaves with every period. Once bleeding passes the 80 mL mark, that figure climbs past 40 mg. Against that, the gut pulls only about 1 to 2 mg of iron a day out of food, which is the arithmetic that explains why a heavy bleeder can eat well, take her supplement, and still lose ground month over month.
It's why supplements alone can feel like they're not doing much. Your body only takes in a fraction of the iron in a pill, and past a certain point a bigger dose doesn't get you much more. So if you're losing a lot each month, you can take iron every day and still watch your levels stay low.
Why Perimenopause Makes Periods Heavier
Perimenopause is one of the main reasons periods get heavy in your forties and fifties. Each time you ovulate, your body makes progesterone, and progesterone is what keeps your uterine lining in check. In perimenopause you ovulate less often, or later, so there's less progesterone around, and estrogen builds that lining up until it sheds as a heavier, less predictable bleed. Some months feel normal, others bring flooding, clots, or a period that drags on for days longer than it should.
Perimenopause isn't the only cause, though. An underactive thyroid can do it, and so can fibroids or adenomyosis, where the lining grows into the muscle wall of the uterus. Those need ruling out, because what may help depends on what's contributing to the blood loss.
Why your bloodwork can look normal when your iron is low
The dismissal usually comes down to how the blood test works. A standard blood count measures your hemoglobin, the iron in active use, and that can read normal while your stored iron is already running out. The storage marker is ferritin, and it isn't always part of routine bloodwork. If nobody checked your ferritin, low iron slips past completely.
Iron deficiency without anemia
Even when ferritin is measured, in range doesn't always mean enough. A lot of labs only flag iron deficiency once ferritin drops below about 10 to 15 μg/L, but symptoms can start when it's under 50. So you can feel the fatigue, the fog, and the breathlessness while your result still reads as technically fine. We go deeper on reading your ferritin in the early signs of low iron.
There's another reason it gets missed. Iron deficiency and perimenopause share almost all the same symptoms: fatigue, brain fog, low mood, poor sleep. So when a woman in her forties says she's wiped out, it's easy to file it under perimenopause and stop there.
What to do when your ferritin comes back low
The first step is knowing where your iron stands, which means testing ferritin. From there it depends on how low you are and how much you're losing each month.
For a lot of women, oral iron rebuilds stores over a few months, as long as it's a form and dose your gut tolerates. When oral iron isn't enough, when it wrecks your stomach, or when your stores are very low, an iron infusion delivers iron straight into the bloodstream and can bring levels up faster. If you're choosing between them, we lay it out in iron infusions versus supplements. Iron infusions are one of the services we offer at Ivy, and you can see how they work on our iron infusion page.
The part that's easy to skip is the bleeding. If heavy periods are draining your iron faster than you can replace it, topping up the iron without dealing with the bleeding lands you right back here in a year. That's why they're worth looking at together, not one at a time.
WHEN THE BLEEDING IS THE BIGGER CONVERSATION
Heavy, changing bleeding deserves attention on its own, and it's part of the bigger picture of perimenopause, a stage to move through with support rather than wait out alone. Sorting out why your periods changed, and what can be done about them, often does more for your energy than any iron number will.
How to tell whether your period counts as heavy
The clinical definition is losing more than 80 mL of blood across a cycle, and nobody measures that at home. What you can go on is what it takes to get through the day. Soaking a pad or tampon every hour for several hours running, passing clots bigger than a loonie, bleeding beyond seven days, doubling up on protection, or setting an alarm to change overnight all put you in the range that deserves a closer look.
Most women underestimate this, because the only period anyone has ever had is their own, and there is no baseline to compare against. If your bleeding has changed from what it used to be for you, that change is the signal, whether or not it meets anyone's threshold.
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If you're tired of being told everything looks fine while you feel anything but, this is the kind of thing we sort out. Book a free 15-minute discovery call and we'll look at your periods and your iron together and figure out what's behind it, so you can feel like yourself again.
FAQ
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Yes, it can contribute for sure! When you ovulate less often, the uterine lining keeps building, so the bleed is heavier, and heavier periods mean more iron lost each month. Over time that loss outpaces what your body absorbs from food and supplements, and your stores fall. The deficiency comes from the blood loss, not the hormone change itself.
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Many labs only flag iron deficiency once ferritin falls below about 10 to 15 μg/L, but symptoms like fatigue and brain fog can start when ferritin is under 50. An in-range result doesn't always mean your iron is where it needs to be. If yours hasn't been tested, or sits at the low end of normal, it's worth a closer look alongside your symptoms.
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Many women start with oral iron, which rebuilds stores over a few months when it's tolerated and the dose is right. An infusion is usually considered when oral iron isn't enough, upsets your stomach, or when ferritin is very low. The right choice depends on your levels, which is why an assessment comes first. We break down the two options in our iron infusions versus supplements post.
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Ivy Health Clinic offers iron assessment and IV iron infusions in Kelowna, at 202-2900 Pandosy St in Pandosy Village. A naturopathic consult reviews your ferritin and your cycle, and infusions are administered by our registered nurse under medical oversight for patients with confirmed iron deficiency. Book a free discovery call at ivyhealthclinic.janeapp.com. Virtual consults are available across BC.
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The symptoms overlap, which is what makes it confusing. Fatigue, brain fog, low mood, and poor sleep show up in both. The way to tell them apart is to measure, by checking ferritin alongside your cycle history. Often both are in play at once, so looking at your iron and your hormones together gives a clearer answer than treating either alone.
This page is for educational purposes only and does not constitute medical advice. Iron testing and treatment are individual, and iron infusions are one tool among many. Speak with your Ivy Health practitioner for personalized interpretation of your results and your options.
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Mansour D, Hofmann A, Gemzell-Danielsson K. A Review of Clinical Guidelines on the Management of Iron Deficiency and Iron-Deficiency Anemia in Women with Heavy Menstrual Bleeding. Adv Ther. 2021;38(1):201-225.
Munro MG, Critchley HOD, Fraser IS, for the FIGO Menstrual Disorders Committee. The two FIGO systems for normal and abnormal uterine bleeding symptoms and classification of causes of abnormal uterine bleeding in the reproductive years: 2018 revisions. Int J Gynaecol Obstet. 2018;143(3):393-408.
Stoffel NU, Cercamondi CI, Brittenham G, 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: two open-label, randomized controlled trials. Lancet Haematol. 2017;4(11):e524-e533.
Last Updated: August 18, 2026
