How much iron do women actually need?

Women aged 19 to 50 need 18 mg of iron a day. Men the same age need 8 mg. That’s not a rounding difference — it’s more than double, and it’s the single largest gap between men and women in the entire set of US dietary recommendations.

The full numbers

These are the Recommended Dietary Allowances set by the National Academies, as published by the NIH Office of Dietary Supplements:

Read down the female column and the story tells itself. Requirements jump at 14, peak through the reproductive years, spike in pregnancy, and then fall back to exactly the male number at 51. Nothing about female physiology needs more iron in general — it’s menstruation, and the recommendation tracks it almost perfectly.

Where the average woman actually lands

Here is the number that rarely makes it into the conversation. According to NIH’s own figures, the average daily iron intake from food among US women over 19 is 12.6 to 13.5 mg.

Against an 18 mg recommendation, the typical woman of reproductive age is running roughly 5 mg short every day — somewhere near a quarter to a third of what she’s meant to be getting. Men, on an 8 mg target, average 16.3 to 18.2 mg. They clear their requirement twice over without trying.

What that does not mean

It does not mean the average woman is iron deficient, and anyone telling you it does is overselling. An RDA isn’t a threshold you drop below and get sick — it’s deliberately set high enough to cover almost everyone in the population, including women at the heavy end of menstrual losses. Plenty of women eating 13 mg a day are completely fine.

What a population-level shortfall does mean is that the margin is thin. When intake sits below the recommendation as a matter of course, the people at the demanding end of the range — heavy periods, pregnancy, endurance training, regular blood donation, a diet without meat — have very little room before short becomes deficient.

And in some groups it clearly has. A 2023 analysis of national survey data found iron deficiency in nearly 40% of US females aged 12 to 21, with 6% meeting the definition of iron-deficiency anaemia. Worth knowing that this used a more sensitive ferritin cutoff than older work, which put the figure closer to 16% — the disagreement is about where to draw the line, not about whether the problem is real.

The number on the label isn’t the number you absorb

Iron is unusual in how little of it actually gets in. Your body absorbs roughly 14–18% of dietary iron from a mixed diet containing meat, seafood and vitamin C — and only 5–12% from a vegetarian one.

Two things drive that gap:

• Heme vs non-heme. Meat, seafood and poultry contain heme iron, which is absorbed far more readily. Everything else — plants, fortified foods, supplements — is non-heme. Heme makes up only about 10–15% of total iron intake in Western diets, but it does a disproportionate share of the work.
• What’s on the plate with it. Vitamin C substantially increases non-heme absorption. Phytates in grains, legumes, nuts and seeds reduce it, as do the tannins in tea and coffee and the calcium in dairy.

This is why the NIH sets the iron recommendation for vegetarians at 1.8 times the standard figure — about 32 mg a day for a woman of reproductive age. Same requirement, much worse exchange rate.

So what should you actually do?

For most people the answer is unglamorous: eat iron-containing foods reasonably often, and put vitamin C next to the non-heme ones. Beans with tomatoes, lentils with lemon, oats with berries. The pairing is doing more work than switching to any particular “high-iron” food.

If you fall into one of the higher-demand groups, or you have symptoms — persistent fatigue, breathlessness on stairs that didn’t used to be there, hair shedding, cold hands, unusual cravings for ice — the useful move is a ferritin test rather than a supplement. Iron deficiency is diagnosed with a blood test, and taking iron you don’t need is genuinely not harmless: the upper limit for adults is 45 mg a day.

Where a bar fits

Honestly: in the gap, not in the treatment. If your ferritin is low enough to need correcting, that’s a therapeutic dose under a doctor, and those doses come with side effects of their own.

The interesting space is the everyday one — roughly 5 mg a day, for a very large number of women, between what they eat and what they’re meant to get. A bar with 25% of the Daily Value is about 4.5 mg. That isn’t a treatment for anything, and we wouldn’t claim it is. It happens to be about the size of the average gap.

Sources

1. Iron — Fact Sheet for Health Professionals — NIH Office of Dietary Supplements
2. Prevalence of Iron Deficiency and Iron-Deficiency Anemia in US Females Aged 12–21 Years, 2003–2020 — Weyand et al., JAMA, 2023