Mind & body, in brief

An adult carries about three to four grams of iron. Most of it is inside the red blood cells that move oxygen. [5][4]

There is no way to get rid of it on purpose. Humans have no working route for pushing iron out of the body. [2]

About one to two milligrams leak away each day, in sweat, in shed gut and skin cells, and in blood. [3][5]

That leak is fixed. The body cannot turn it up when it holds too much, or turn it down when it is short. [2]

So the only control that can be adjusted is how much gets absorbed. Iron balance is held at the gut wall and nowhere else. [2]

Almost none of your iron comes from food. About 20 mg a day is recycled from worn-out red cells; only 1 to 2 mg is absorbed. [3]

A liver hormone called hepcidin works that control. It sticks to ferroportin, the doorway iron leaves a cell by, and destroys it. [1][3]

Ferroportin is the only known protein that moves iron out of a cell. Shut it and the iron stays where it is. [2][10]

Hepcidin also rises with inflammation. An infection shuts the gut door whether or not you need iron. [3][34]

Ferritin, the storage protein, is a hollow ball that packs iron away. That is containment, not removal. [54]

When storage runs out, iron circulates loose instead of bound to its carrier. Loose iron is the toxic form, and it can enter any organ. [2]

In hereditary haemochromatosis the hepcidin signal is faulty, so the gut keeps absorbing. About 1 in 150 people of northern European ancestry carry the main double gene change. [6][7]

Left unmanaged, that slow loading ends in cirrhosis, or permanent liver scarring, in about 70% of patients. About half of people with the double gene change develop diabetes. [6]

There is no cure. The standard treatment is drawing blood, because most of the body's iron sits inside red cells. [8]

One bag of donated red cells carries 200 to 250 mg of iron, roughly 100 to 150 days of ordinary absorption, delivered at once. [9]

Shortage is the far commoner problem. Iron deficiency is the most common mineral shortage in the world, affecting around two billion people. [25]

Why it matters. Watch the thresholds rather than the treatments. Several 2025 papers argue the ferritin cut-offs for calling someone iron deficient are set too low. Raising one of them doubled the share of young children counted as short. [18][15]

A retrospective look at 33,029 private health-check samples found anaemia in 6.0% of people overall, 9.9% of women, and outright iron deficiency in 31.6% of women. [14]

Why it matters. These are people well enough, and well off enough, to buy a health check on themselves.

In 100 non-pregnant women with a normal level of haemoglobin, the oxygen-carrying protein in blood, 41% were iron deficient on a ferritin test. History of breastfeeding raised the odds nearly sevenfold. [16]

Why it matters. The blood count is the test most people get, and it is the last thing to move.

Using a ferritin cut-off of 22 micrograms per litre, iron deficiency in children aged 6 to 59 months reached 34%, against 16% at the WHO figure. [18]

Why it matters. Nothing changed in any child; the definition changed, and the disease doubled.

A Lancet Haematology Commission puts anaemia at over 1.9 billion people and calls the 50% reduction target unachievable, proposing 12-22% instead. [12]

Why it matters. The target was set on ambition rather than on what the available tools can do.

Dietary iron shortage accounts for roughly 66% of anaemia worldwide: an estimated 444 million cases in men and 825 million in women. [11]

Why it matters. It is a nutrient problem before it is a blood problem.

Sixty iron-deficient women were given either 60 mg daily or 120 mg on alternate days for 14 days. Daily doses did better on red cell size and haemoglobin content. [20]

Why it matters. The popular alternate-day advice rests on hepcidin reasoning that this trial did not reproduce.

In the PANDA trial, 135 non-anaemic pregnant women took iron daily, on alternate days or three times a week. At 26 to 30 weeks, 69% to 72% were still iron deficient. [21]

Why it matters. Pregnancy raises the demand faster than the gut can pass iron through.

Ascorbic acid stops iron forming compounds the gut cannot take up, and converts iron to the form the gut transporter accepts. [23][24]

Why it matters. It changes what arrives at the door, not what the door decides.

Some studies put the drop in iron availability from eggs at about 27% in adults. Calcium supplements, antacids and acid-blocking drugs also cut absorption. [26][22]

Why it matters. Two people eating the same iron can absorb very different amounts of it.

Among 252 donors at a teaching hospital in Tamale, Ghana, 40.1% had ferritin under 30 ng/mL and 14.7% were iron deficient. Low stores were commoner in repeat donors. [27]

Why it matters. Donation is the body's only real exit, and using it has a price attached.

Iron given into a vein is taken up completely, bypassing the gut control. A network meta-analysis of 13 trials found it cut heart-failure hospital admissions. [18][30]

Why it matters. The one regulated step in the whole system can simply be gone around.

Across five trials and 6,038 patients, repeat hospital admission or death from heart disease fell by about a quarter in the year after ferric carboxymaltose, one of the iron drips. [29]

Why it matters. Iron deficiency affects between 37% and 75% of heart-failure patients, depending on the definition used. [28]

Seven trials covering 975 patients found high-dose iron given by drip reduced the rate of red cell transfusion after cardiac surgery. [31]

Why it matters. A transfusion avoided is 200 to 250 mg of iron the body never has to hold.

Across 339,145 records, matched one to one, patients given iron by drip during an infection survived better at 14 and 90 days. The infections were MRSA in the blood, pneumonia, urinary infections and colitis. [32]

Why it matters. Bacteria need iron too, which is why withholding it during infection was the standing worry.

In 149 patients with a disease that stiffens the heart with abnormal protein, iron deficiency ranged from 40.9% to 70.5% depending on which of three definitions was used. [33]

Why it matters. Only the two availability-based definitions predicted who died.

A review of 47 studies in inflammatory bowel disease found hepcidin rising alongside the two standard blood markers of inflammation, while iron and haemoglobin fell. [34]

Why it matters. The same signal that hides the shortage is the one causing it.

Among 112 people with ulcerative colitis and no anaemia, 33.9% were iron deficient. Non-healed gut lining raised the odds eighteenfold. [35]

Why it matters. Anaemia is a late sign, and waiting for it means waiting years.

A Cleveland Clinic clinician notes that everything flags normal between 15 and 200 ng/mL, while many clinicians aim for at least 50 in young athletes. [38]

Why it matters. A high-school cross-country girl runs 30 to 35 miles a week, and a Division I collegiate runner up to 100.

In 23 young women with iron-deficiency anaemia, eight weeks of iron improved fatigue scores and muscle endurance. Aerobic fitness and muscle strength did not move. [39]

Why it matters. It is a small uncontrolled trial, and it still separates two claims usually sold together.

Across 23 randomised trials and 1,005 patients, deferiprone improved heart pumping. It did not significantly change ferritin, liver iron or the heart scan, and side effects were more common. [43]

Why it matters. The drug exists to install the exit the body lacks, so what it removes is the whole point.

Of 60 children on oral iron-removing drugs, 16.6% had some hearing loss. In a Turkish cohort, hormone problems fell from 83% to 25.8% over about six years of treatment. [44][45]

Why it matters. Both numbers describe the same trade: damage prevented against damage caused.

The US neurological institute lists ten disorders in which iron builds up in the brain. One is caused by a faulty version of a protein whose job is clearing extra iron out of cells. [42]

Why it matters. When the local clearing fails, the accumulation is in a place nothing can be drained from.

Among 200 patients with cirrhosis, 68.5% of those with raised ferritin had a complication within a year, against 27.7% of those with normal levels. [47]

Why it matters. Ferritin is being read less as a fuel gauge and more as a stress signal.

Researchers engineered food-grade bacteria to release hepcidin straight into the intestine. It cut the gut's iron transporter and countered overload in mice. [49]

Why it matters. It is an attempt to work the door from the outside rather than replace the hormone in the blood.

In records of anaemic women aged 15 to 49 across Indian regions, iron deficiency was the leading cause in 95.8% of cases; 9.4% were severe. [51]

Why it matters. Where the food supply is thin, the door is not the limiting step.

The 2021 global burden estimate puts anaemia at 24.8% of the world's population, more than 1.6 billion people, with the heaviest load in under-fives and in women of reproductive age. [13]

Why it matters. The count keeps rising even as the rate per person falls, because there are more people.

A review of 55 studies covering 2.1 million children aged 5 to 12 found iron-deficiency anaemia in 9.4%, rising to 21.9% in sub-Saharan Africa and 29.7% in low-income countries. [17]

Why it matters. Programmes are aimed at pre-schoolers and women, so this group is measured last.

The recommended intake for women is 18 mg a day up to age 50 and 8 mg from 51, against 27 mg in pregnancy. Iron-deficiency anaemia still affects up to 17% of Americans over 65. [19]

Why it matters. A gerontologist's line for it: after menopause a woman is not meant to be losing iron, so a falling level needs a reason.

Anaemia is reported in 30% to 94% of tuberculosis patients. A study in Port Sudan put iron-deficiency anaemia at about 16% of them. [36]

Why it matters. Long infection keeps hepcidin high, so iron is locked away rather than absent.

Researchers tested 238 children aged 6 to 72 months in southern Peru. They combined the ferritin reading with a second measure, how loaded the blood's iron carrier is, to tell overload apart from inflammation. [37]

Why it matters. Both push ferritin up, and the treatments point in opposite directions.

Ferroptosis, a form of cell death that runs on iron and collapses the cell's own antioxidant defence, is now a live research line in Alzheimer's disease. [41]

Why it matters. Iron accumulates in ageing brains, and nobody has yet shown which way the causation runs.

Normal haemoglobin in pregnancy is 11 g/dL or above in the first and third trimesters, and 10.5 in the second. Ferritin under 30 ng/mL is the preferred marker of low stores. [50]

Why it matters. The thresholds move by trimester, which the general iron guidelines do not.

Among 672 anaemic patients at one Indian hospital, 38.2% had iron-deficiency anaemia and 41.2% of those also had inflammation running alongside it. [53]

Why it matters. That overlap is exactly where a ferritin number stops being readable.

A review found ADHD symptom severity higher in children with iron deficiency, and an association between the two, though ferritin values overlapped heavily and unmedicated children showed no difference. [40]

Why it matters. It is an association looking for a mechanism, not a finding.

Among 53 transfusion-dependent beta-thalassemia patients in Sana'a, iron levels were markedly higher in those transfused for more than five years or receiving over 250 mL at a time. [46]

Why it matters. Dose and duration, and nothing the body does, decide the total.

Fifty-six Indian children with a form of thalassemia that needs no regular transfusions had liver and heart iron scanned and compared with their ferritin readings. [52]

Why it matters. Ineffective red-cell production suppresses hepcidin, so the gut over-absorbs with no transfusion involved.

Among 3,424 patients with coronary disease and chronic heart failure, those above a ferritin of about 230 ng/mL did worse than those below it. [48]

Why it matters. High ferritin here is read as inflammation and damage, not as a full tank.

A scoping review of hereditary haemochromatosis found the standard quality-of-life questionnaire covers neither joint pain nor fatigue in detail, the two things patients raise first. [55]

Why it matters. A disease scored on liver enzymes is not scored on how it feels.