I’ve been tracking my iron panel every two weeks. Not because anything alarming is going on, but because I got tired of my iron doing whatever it felt like and having nothing to compare it against. I wanted data I could actually work from.
Last week my ferritin went up. So did my CRP, which is a marker of inflammation, and I’d been ill the week before.
So the number that’s supposed to tell me how much iron I have in reserve went up for reasons that had nothing to do with iron.
That’s a small, irritating version of something that happens on a much larger scale in perimenopause. Several of my friends are starting perimenopause. I’m not (I think).
But I went looking at what ferritin does during the transition, and it turns out the same thing happens there, for different reasons.
Researchers looked at 337,218 hemoglobin and 171,542 ferritin tests from new Dutch blood donors. Hemoglobin peaked around 10:30 am (9:40 am in women over 45), and both markers ran higher in winter than in summer. The shifts are small and won’t change most results. If your number sits near a cut-off, the time and season of the blood draw can decide which side of it you land on.
The study covered about 15,300 pregnant women at 25 clinics serving Palestine refugees in Jordan. Clinics that gave a 15-nutrient multivitamin saw about a third less mid-pregnancy anemia than clinics using the standard iron-folic acid tablet. The multivitamin has less iron per tablet, but women stuck with it better: fewer ran out (2–8% vs 19–31%) and fewer got constipated (8–13% vs 19–28%). Each clinic, not each woman, was assigned a supplement, and the foundation that funded the study donated the multivitamins.
A review of 570 resistance-training studies found that 72% recruited only men, 11% only women and 17% both. Fewer than 1 in 10 studies that included women accounted for menstrual cycle phase. Male-only studies were nearly four times as likely to run molecular analyses as studies that included women. Women and men gain muscle at broadly similar relative rates, so standard training advice likely holds for women, but the evidence behind it comes mostly from men. Recruitment of women has improved slightly since 2020.
Lalmin Iron is an ingredient sold to supplement and food makers, not a product you can buy yet. The iron sits inside yeast cells and is released as the yeast is digested, instead of being added as an iron salt. Its only evidence is a two-week pilot in 14 young, active women. They ate cookies with 40 mg of iron every other day and reported no increase in gut symptoms. Every-other-day dosing reduces side effects on its own. The pilot didn’t check whether ferritin rose or compare the yeast with a standard iron salt.
Your periods change in your forties. Some of them run nine, ten, eleven days. You are tired in a way sleep does not fix.
In perimenopause, you can be losing more iron than at any earlier point in your life. The paradox is that your blood tests can show higher iron stores than before.
Your periods are not just changing. They’re getting longer.
1,320 women kept daily period calendars for 10 years. Measured against their own cycles from before the transition, periods of 10 days or more became 3x as likely in early perimenopause and 4x as likely in late perimenopause (oh, joy). Over those years, 77.7% had at least 3 periods lasting 10 days or longer.
So it’s not that every period gets heavier. It’s that you start getting occasional very long ones, again and again. Iron loss adds up by total volume.
Meanwhile, your ferritin is climbing.
Ferritin is the protein that stores iron. Doctors look at how much is in your blood to judge your reserves. Across the transition, it goes up, which sounds like it makes sense. Periods stop, so iron loss presumably diminishes, and so your tank refills.
The problem is that ferritin stops matching your other iron markers. In 1,885 women followed through their last period, hemoglobin, serum iron, and transferrin saturation all rose and then flattened out, while ferritin rose and kept rising.
What the extra ferritin is actually tracking
That gap “cannot be solely attributed to changes in iron stores.” They checked what the extra ferritin was tracking.
In some women, the level was higher than their available iron could account for. Those women had fatty liver 3x as often, 21.9% vs. about 8%, along with higher triglycerides and blood sugar.
Their ferritin was reporting metabolic strain, not iron stores.
Less iron is getting in too
There may be a second reason the iron losses bite harder. Your gut isn’t absorbing all the iron you eat.
Estrogen pushes hepcidin down, the hormone that limits how much iron your gut absorbs. In 153 women, higher estrogen went with lower hepcidin and more iron available in the blood.
Estrogen declines across the transition. You’ll be absorbing less in the same years you’re losing more. This is the hypothesized causal pathway, however. We still need to measure this last stage in perimenopausal women to get concrete evidence.
Nobody has studied both halves together
Bleeding research and ferritin research have never been done in the same women.
As of October 2026, PubMed, Europe PMC, and the trial registries show no study measuring period blood loss and iron status together across the stages of the transition into menopause.
There is no ferritin threshold built for perimenopausal women specifically. One study is registered, an interventional trial of 240 women looking at perimenopausal heavy bleeding, quality of life, and cognition. But it hasn’t yet started recruiting.
📅 Record the start and end date of every period.
Length is what shifts during the transition, not heaviness. Periods of 10 days or more become three times more likely in early perimenopause and four times more likely in late perimenopause, and the typical period does not change at all.
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