If you've been around here long enough, you'll know that 18 months ago I had a baby and I breastfed her. I stopped when she was around 10 months, so I'm at about 8 months of being done breastfeeding.
I have to report also that a year ago, while I was still breastfeeding, my ferritin was at 100. Now it's back at 40. The major change that has happened since is that my period returned once I finished breastfeeding.
The question that this leads to is: how can my periods so regularly drain me of my iron and energy?
I’m diving deep into iron loss today: what it means to have a heavy period versus a light one, and what it actually takes to replenish what you lose
Researchers measured 21 active women in the early follicular, ovulatory and mid-luteal phases, with timing confirmed by ovulation tests. Resting metabolic rate didn’t differ between phases. Women ate about 25 g more carbohydrate early in the cycle than mid-luteal. Body weight shifted by 0.3 kg, and the authors attribute that to water, not fat or muscle. It’s a small study, but it runs against cycle-syncing advice to eat more in the luteal phase because metabolism speeds up.
The Irish ROLO cohort followed 196 mothers, average age 43, almost all still premenopausal. 71% had ever breastfed, and 40% had breastfed for 12 months or more in total. Breastfeeding duration, exclusive or any, showed no link with DXA bone measurements a decade on. The authors say this reassures women that breastfeeding has no lasting negative effect on bone. 171 women had DXA scans.
The TikTok trend claims pale skin, dark circles and a tired face reveal low ferritin. It is not a medical diagnosis. Iron-deficiency anemia can make skin paler, but low ferritin without anemia usually leaves no visible sign. Only a blood test measures ferritin, and a hemoglobin test alone can miss low stores. Taking iron without a test risks overload in people with hemochromatosis.
Zydus’s patch delivers estradiol 0.045 mg and levonorgestrel 0.015 mg a day, changed once a week, for women with a uterus. It treats moderate to severe hot flashes and night sweats and helps prevent postmenopausal osteoporosis. The FDA rates it therapeutically equivalent to Bayer’s brand. It arrives as estrogen patches have been hard to fill since the boxed warning came off menopause hormone therapy. Zydus hasn’t announced a launch date or price, so the savings are still unknown.
An average period costs you about 12 mg of iron. Food gives you back about 0.9 mg a day (if you actually reach the recommended 18 mg daily intake!), so replacing one average period takes about 13 days of eating.
At 80 mL, the official cutoff for a heavy period, you need about 35 days. Unless you have long cycles, your next period starts before the end of those 35 days.
An average period takes 13 days of eating to replace
In 1964, researchers collected the used pads and tampons of 38 healthy women and measured the iron in them. The average loss was about 12 mg per period, which filled under two fully soaked regular pads (25 mL of blood).
Some women lost under 3 mg of iron. Others lost more than 30 mg. That means that, in theory, the woman who lost 3 mg replaced it in 3 days, while the woman who lost 30 mg needed 33 days. It’s worth mentioning that both of these women have periods a doctor would call normal.
In 14 women at a clinic for heavy bleeding, losses ran from 6 mg to 53 mg. at the top of that range, replacing one period of iron loss takes about 59 days of eating. You would need two months without bleeding to get back to where you started.
The heavy-period cutoff is an iron calculation
80 mL is the usual cutoff for a heavy period, and 5 or 6 fully soaked regular pads hold that much. it comes from a 1966 study of 476 women picked at random whose average period filled about three pads (43.4 mL).
The authors calculated the cutoff instead of measuring which women became ill. Over a 28-day cycle, 0.9 mg a day adds up to about 25 mg of iron. 25 mg is the iron in about 4 fully soaked pads (63 mL). 4 pads a month is the most your food can keep up with. 5 or 6 pads, the official cutoff, works out at about 32 mg. Replacing that takes 35 days, and your next period arrives, presumably, after 28.
So what does that mean? Four pads is break-even. The cutoff is at five or six. Periods in that gap are normal by every guideline in use, and they still take more iron than food can replace.
Bottom line: You do not have to have a heavy period to be losing more iron than you take in.
Can you measure this yourself?
Yes, within limits.
Across one period, weigh every used pad, subtracting the weight of an unused one of the same kind, and add up the grams. Fluid weight tracked the laboratory measurement closely.
What you weigh, of course, is not pure blood. It’s blood mixed with shed womb lining and other secretions. Blood is only 48% to 50% of it when bleeding is moderate or heavy. That share rises as the volume rises, so grams do not convert into milliliters of blood.
While you'll be able to track for yourself whether a particular period is lighter or heavier using this approach, we haven't been able to set a number of grams that counts as heavy because totals from normal periods and heavy ones overlap on modern pads.
In the past, studies have scored pads against a chart of drawings instead, but they generally haven't been very reliable. No standard chart exists for general practice.
🩸 Count the pads you soak right through, for one period.
Tally them in your phone as you go, then write down the total and the date. Compare that total to your next one. For a finer number, weigh each used pad and subtract the weight of a dry one.
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