How Much Iron Should You Take During Your Period?

Most menstruating adults need about 18 mg of elemental iron per day from food and supplements combined, roughly double the amount recommended for men and postmenopausal women. That baseline number, set by major dietary guidelines, accounts for the iron lost in menstrual blood each cycle. But whether you actually need a supplement on top of your diet, and at what dose, depends on how heavy your periods are, what you eat, and whether your iron stores are already low. The answer is less about a single number and more about matching your intake to your losses.

How Much Iron You Lose Each Cycle

A woman with a typical period loses roughly 1 mg of iron per cycle. That might sound trivial, but iron is poorly absorbed from food, so you need to eat far more than 1 mg to replace that 1 mg. In women with heavy menstrual bleeding, the picture changes dramatically: average iron losses jump to about 5 mg per cycle, and values as high as 8 or 9 mg have been documented. Most of those women had completely depleted iron stores, with ferritin levels averaging around 6 ng/mL compared to about 36 ng/mL in women with normal periods.¹

The gap between “normal” and “heavy” matters because it determines whether diet alone can keep up. If you lose 1 mg of iron per cycle and absorb roughly 10–15% of the iron you eat, the standard 18 mg dietary recommendation covers you. If you lose five to six times that, no amount of spinach is going to close the gap without help.

When You Probably Need a Supplement

Heavy menstrual bleeding is one of the most common reasons premenopausal women develop iron deficiency and iron deficiency anemia.² Periods lasting more than eight days, or cycles involving clots or flooding, raise the odds of iron deficiency anemia by three to six times.³ And the downstream effects are measurable: among women who report heavy periods, roughly a third have hemoglobin below the normal threshold, compared to just 4% of women with lighter flow.⁴

If your periods are consistently heavy and you feel fatigued, short of breath with mild effort, or notice brittle nails and unusual cravings, those are classic signs that your iron stores may be running on empty. A blood test is the only way to confirm it, but heavy bleeding alone is a strong enough risk factor that many clinicians will start a conversation about supplementation without waiting for symptoms.

Choosing a Dose and Schedule

Treatment doses for iron deficiency typically range from about 30 to 65 mg of elemental iron per day, depending on how depleted your stores are. But here is where the research has shifted in an interesting direction: you may not need to take iron every single day to get results, and doing so might actually work against you.

When you take an iron supplement, your body produces a hormone called hepcidin that temporarily blocks iron absorption. This hepcidin spike lasts about 24 hours, which means a second dose taken the next day gets absorbed less efficiently. In iron-deficient women, absorption on alternating days was 40–50% higher than on consecutive days.⁵ Your body essentially puts up a wall after the first dose, and the wall doesn’t come down until the next day.

This finding has been backed by clinical trial data comparing the two approaches head-to-head. One trial gave women either daily iron for 90 days or alternate-day iron for 180 days. Both groups ended up at virtually the same ferritin level, around 44 μg/L. But at the six-month follow-up, the alternate-day group actually had lower rates of iron deficiency. And the daily group reported nearly twice the rate of gut side effects.⁶

A large Cochrane review of intermittent versus daily supplementation in menstruating women found similar patterns: comparable effects on anemia rates and hemoglobin, with fewer side effects in the intermittent group. Women on intermittent schedules were less than half as likely to report adverse effects.⁷ The trade-off is that ferritin levels tend to rise a bit less with intermittent dosing, so if you’re severely depleted, your clinician may still prefer daily dosing for a short course to build stores faster before switching to an every-other-day maintenance plan.

Which Form of Iron Supplement to Pick

Walk into a pharmacy and you’ll see ferrous sulfate, ferrous fumarate, ferrous bisglycinate, ferrous ascorbate, and newer options like sucrosomial iron. They are not interchangeable.

Ferrous sulfate is the oldest and most studied form. It is cheap and effective at raising ferritin, though it is also the most likely to upset your stomach. In one trial comparing several oral iron forms in women with iron deficiency anemia, sucrosomial iron produced the largest improvements in both hemoglobin and ferritin levels and had the best safety profile.⁸

Ferrous bisglycinate (also called iron bisglycinate chelate) is marketed as gentler and better absorbed, and there is some evidence for that. In a trial with Mexican schoolchildren, bisglycinate chelate maintained higher ferritin levels six months after supplementation ended compared to ferrous sulfate.⁹ However, a trial in Cambodian women found that 18 mg of ferrous bisglycinate was not as effective as 60 mg of ferrous sulfate at raising ferritin, though the doses were intentionally unequal to test whether bisglycinate’s higher bioavailability could compensate for a much smaller dose.¹⁰ The bottom line is that milligram for milligram, bisglycinate is better absorbed, but if the dose is dramatically lower, it may not fully make up the difference.

Newer formulations like ferric maltol and sucrosomial iron attempt to reduce gut irritation by changing how iron is delivered. Early evidence is promising, but these products tend to cost more, and head-to-head data against traditional forms are still accumulating.¹¹

What You Eat Alongside Your Supplement Matters

Iron absorption doesn’t happen in a vacuum. Certain nutrients dramatically boost or block how much iron your gut actually takes in. Ascorbic acid (vitamin C) is the strongest enhancer: it converts iron into a form that stays soluble in the small intestine, where absorption occurs. Taking vitamin C alongside your iron supplement can increase absorption by a factor of two to four.¹² A glass of orange juice or a vitamin C tablet with your iron pill is one of the simplest things you can do to get more out of each dose.

On the other side, several common dietary compounds interfere with absorption. Calcium, phytates (found in whole grains, legumes, and nuts), and polyphenols (in tea, coffee, and red wine) all reduce how much iron gets through. Calcium is unusual because it blocks both plant-based and meat-based forms of iron, while phytates and polyphenols mainly affect plant-based iron.¹³ The practical takeaway: try to separate your iron supplement from your coffee, tea, or calcium-containing foods by at least an hour or two. And if you take both iron and calcium supplements, take them at different times of day.

Why Gut Side Effects Happen and How to Handle Them

Stomach cramps, nausea, constipation, and dark stools are the most common complaints with iron supplements, and they’re the main reason people quit taking them. The cause is straightforward: most of the iron in a standard-dose pill doesn’t get absorbed. It passes through to the lower intestine, where it generates oxidative stress that damages the gut lining and shifts the balance of gut bacteria in unfavorable directions.¹⁴

Unabsorbed iron also feeds certain gut bacteria, including potentially harmful species. High doses of iron can increase populations of pathogenic bacteria while reducing beneficial ones like bifidobacteria and lactobacilli.¹⁵ A trial in Cambodian women specifically showed that iron supplements increased the relative abundance of Enterobacteriaceae, a family that includes several harmful species.¹⁶

This is one reason the alternate-day dosing approach has gained traction. Fewer pills mean less unabsorbed iron sitting in your gut, which translates to fewer side effects. If daily dosing still feels rough even at a low dose, taking your supplement every other day is a reasonable compromise that the evidence supports. When oral iron is truly intolerable or not working, intravenous iron therapy can bypass the gut entirely, though that requires a clinical setting.¹¹

Getting Tested and What the Numbers Mean

Ferritin is the most common blood marker used to assess iron stores, and the threshold for “deficient” is more contested than you might expect. The World Health Organization has traditionally set the cutoff at 15 ng/mL, but researchers have increasingly argued this is too low and misses a large number of people who are functionally iron deficient. Recent work suggests that a ferritin level below 50 ng/mL may be a more accurate threshold for adults, better aligning with the level at which the body starts ramping up iron absorption in response to low stores.¹⁷

For premenopausal women specifically, one study using physiological data estimated the optimal ferritin threshold at about 25 μg/L, which is still higher than the WHO’s traditional cutoff but lower than the proposed 50 μg/L general threshold.¹⁸ This discrepancy is worth knowing about, because if your doctor tells you your ferritin is “normal” at 16 ng/mL based on the old WHO cutoff, you could still be experiencing real symptoms of depletion. If you feel lousy and your ferritin is in the 15–30 range, it is reasonable to push for a conversation about supplementation.

Ferritin can also be misleading during illness or inflammation, since it rises as part of the body’s acute-phase response. If you’ve been sick recently or have a chronic inflammatory condition, a single ferritin reading may overstate your actual iron reserves. In those cases, your clinician might also check transferrin saturation or soluble transferrin receptor levels to get a clearer picture.

Vegetarian and Vegan Diets Add Another Layer

Plant-based iron (non-heme iron) is absorbed less efficiently than the heme iron found in meat, poultry, and fish. That difference has real consequences for menstruating vegetarians and vegans. A study comparing 50 vegetarian and 50 non-vegetarian women of reproductive age found that average ferritin levels in the vegetarian group were about 21 μg/L versus 37 μg/L in omnivores. Vegetarian women were also about three times more likely to experience menstrual disorders like painful or irregular periods, and having a ferritin level below 30 μg/L independently raised the odds of menstrual problems.¹⁹

If you eat no animal products, you can still meet your iron needs, but it requires more intention. Pairing iron-rich plant foods (lentils, fortified cereals, tofu, dark leafy greens) with a vitamin C source at the same meal is the single most effective dietary strategy. And because absorption inhibitors like phytates are more prevalent in plant-heavy diets, a low-dose iron supplement may be worth considering as insurance, especially during heavier-flow months.

Female Athletes and Iron Drain

Exercise adds a second drain on iron beyond menstruation. Endurance activities increase iron losses through several pathways: foot-strike hemolysis (red blood cells breaking down from repeated impact), iron lost in sweat, and gastrointestinal bleeding that can occur with intense exertion. Female athletes who menstruate face a double hit.²⁰

Iron balance in active women is also complicated by hepcidin, the same hormone that limits absorption after a supplement dose. Intense exercise itself triggers a temporary hepcidin spike, which means training right after taking an iron pill could reduce how much you absorb. Timing your supplement to a rest day or well away from a hard workout session can help.²¹ Many sports-medicine practitioners recommend periodic ferritin screening for menstruating female athletes, even those who feel fine, because performance can decline before full-blown anemia develops.

Teenagers and the Growth-Period Double Demand

Adolescent girls face a particularly high iron requirement because menstruation begins at the same time the body is growing rapidly. The growth spurt expands blood volume and lean body mass, both of which demand iron. Estimated iron needs for adolescent females can reach 2.2 mg per day of absorbed iron or even higher in those with heavy periods.²² Since only a fraction of dietary iron is absorbed, the amount they need to eat is substantial. Teenage girls who are picky eaters, dieting, or following plant-based patterns without careful planning are at especially high risk of developing deficiency during these years.

How Hormones Quietly Adjust Iron Absorption

The body has a built-in mechanism to compensate for menstrual iron loss that most people never hear about. Estrogen, which rises and falls throughout the cycle, directly suppresses hepcidin, the hormone that blocks iron absorption. When estrogen levels are higher, hepcidin drops, and your gut lets in more iron. Research in liver cells and in mice has confirmed that estradiol (the primary form of estrogen) acts on the hepcidin gene to turn down its expression.²³ This pathway appears to work through a specific receptor on liver cells, and when estrogen is removed experimentally, iron absorption goes up in the gut but body iron storage also shifts.²⁴

This hormonal connection has practical implications for women on hormonal contraception. Oral contraceptive pills typically lighten menstrual bleeding, which directly reduces iron loss. In a large Danish study of over 1,300 women, those using oral contraceptives had higher ferritin levels and fewer depleted iron stores than non-users.²⁵ If you’ve recently stopped hormonal birth control and noticed heavier periods, your iron needs may have changed, and it’s worth getting a ferritin check a few months after the switch.

The Ferritin Threshold Debate and What It Means for You

The tension between the old WHO ferritin cutoff of 15 ng/mL and the newer proposed thresholds around 25–50 ng/mL is not just an academic debate. It directly affects whether your doctor tells you you’re fine or starts you on a supplement. Women who regularly menstruate, particularly those with heavier flow, tend to hover in a ferritin range that looks “normal” by old standards but may actually represent early depletion. Ovulatory women with regular cycles show higher rates of iron depletion compared to women who are not menstruating at all.²⁶

If your ferritin sits between 15 and 30 and you have symptoms like fatigue, brain fog, restless legs, or hair thinning, do not accept “you’re fine” as a final answer. These symptoms can appear well before hemoglobin drops enough to qualify as anemia on a standard blood count. Asking specifically for a ferritin test, rather than just a complete blood count, is the right move, because hemoglobin is the last marker to fall in iron depletion. Your stores can be nearly empty while your hemoglobin still looks normal.

A Practical Framework for Deciding Your Dose

There is no one-size-fits-all milligram number, but you can use a rough framework based on your situation:

Normal periods, balanced diet: You likely meet the 18 mg daily recommendation through food alone, especially if you eat some red meat or iron-fortified foods. No supplement needed unless blood work says otherwise.
Normal periods, plant-based diet: A low-dose supplement in the range of 18–30 mg of elemental iron every other day is a reasonable insurance policy, paired with vitamin C at the same meal.
Heavy periods or confirmed low ferritin: A clinician-guided dose in the range of 30–65 mg of elemental iron, ideally on an alternate-day schedule to maximize absorption and reduce side effects, until ferritin recovers. Recheck levels after two to three months.
Severe deficiency or anemia with symptoms: Higher doses or even intravenous iron may be appropriate. This is not a self-treat situation. Work with your doctor.

Whatever dose you settle on, remember that the elemental iron content is what matters, and it varies by formulation. A 325 mg tablet of ferrous sulfate contains about 65 mg of elemental iron. A 300 mg tablet of ferrous gluconate contains roughly 35 mg. The label should list elemental iron specifically; if it doesn’t, you’re guessing.

Take your supplement on an empty stomach if you can tolerate it, or with a small amount of food containing vitamin C if you can’t. Avoid taking it within two hours of coffee, tea, dairy, or calcium supplements. And if you choose the every-other-day approach, keep a simple calendar or set a phone reminder so you don’t accidentally double up or skip too long.