Iron

The trial's one favourable repletion number is a secondary outcome at p=0.049 resting on roughly 2 women against 8, which is too few to build on. It ran at a single centre in 150 young Swiss women, none of them anaemic, so it does not establish the same schedule in men, in older adults, or in anyone with iron-deficiency anaemia.

Doses across the pooled trials ran from 7 to 1,800 milligrams of iron a day, schedules that are not clinically interchangeable. 27 of the 38 studies left out first-time donors, who are the people least likely to come back after being turned away and therefore the ones the intervention most needs to reach. The review was produced by a national blood service, which has a direct operational interest in donor retention.

The 30 microgram figure rests on 9 studies and 512 people, all graded low or very low certainty. The studies underneath it proposed thresholds anywhere from 12 to 200 micrograms per litre. And ferritin was far worse at spotting iron overload than deficiency.

Fifty-four young Swiss women, split across three sub-studies, all with low iron stores and none anaemic. What was measured is how much iron crossed the gut over a day or two, not haemoglobin or stores rebuilt over months. The paper argues the hepcidin timing supports alternate-day dosing but never tested such a schedule.

People carrying only one copy, and those with the milder H63D variant, showed no excess of anything — and they far outnumber the two-copy group, which is roughly 1 in 150 to 200 people of northern European ancestry. UK Biobank volunteers are healthier than the general population, so these percentages are not population rates. The one-in-ten lifetime figure is for men; the figure for women is substantially lower.

Only 10 of the 67 trials were judged at low risk of bias. The harm figures rest on far fewer women than the benefit ones — 521 to 604 against 6,861 for haemoglobin — so they are much less precise. The review's composite measure of any side effect at all was not significant, even though the specific ones were.

The iron dose was 100 milligrams every eight hours, high enough that absorption is already saturating and there is little room for an enhancer to help. Everyone in the trial was frankly anaemic, in whom absorption is already turned up. And this tested a vitamin C tablet taken with an iron tablet, not the vitamin C in a meal acting on the iron in food.

Neither finding comes from a trial designed to test the pairing: one is a subgroup pattern and the other a set of marker outcomes graded very low to moderate certainty. The usual explanation, that two similar metals compete for the same route into the body, is not tested by either source. All of it concerns children given substantial doses of both minerals in settings where deficiency is common, not the small amounts in a multivitamin.

The subgroup finding that carries this claim is reported without a formal test of interaction, so it is suggestive rather than demonstrated. Six of the eighteen studies had no control group, and their effect sizes run two to three times larger, which is what an uncontrolled design predicts. Only 204 of the 1,408 participants were children or adolescents.

These are modelled ranges built from intake data and isotope studies, not measurements taken in one population, which is why they are given as spans rather than single numbers. The review is a narrative one and lists the nature of the meat factor, and the roles of vitamin A and carotenoids, as still unresolved.

Poison-centre and poisons-service data are voluntary referrals rather than a census, so a count of zero deaths describes the cases that reached them. The UK cohort counts hospital referrals, which would miss a child who died before or too soon after arriving. And the US figures stop in 1998, straddling the 1997 packaging rule without separating out its effect.

This is a narrative review, so which studies went into it was the authors' judgement, and they work at the laboratory that produced much of the underlying isotope work. The two-week comparison rests on a single cited study. And single-meal effects are real, so this deflates the advice rather than cancelling it.

Every study underneath these means was observational. The 70 micrograms per litre comparator rests on three studies and 151 people. The inflammation correction is a statistical adjustment to survey data rather than a check against bone marrow, and the two proteins it needs are not measured alongside an ordinary ferritin test.

This is one manufacturer's label. Other iron salts — fumarate, gluconate, bisglycinate — deliver different amounts of elemental iron per tablet, so the ratio here is not a conversion factor for every product. The label itself carries three disagreeing revision dates, so treat it as a record of what a shopper is told rather than of when they were told it.

The review mixes randomised trials with observational studies. Its haemoglobin and ferritin figures came out with heterogeneity of 91% and 87%, which makes those pooled numbers too unstable to quote as point estimates. What is left is a benefit measured in blood tests and a diagnosis avoided, not in how the pregnancy or the baby turned out.

The authors read the older peak as intentional rather than accidental, which is an interpretation of the age and sex pattern rather than something the referrals recorded. These are hospital referrals to a poisons service, not all iron overdoses. And how much iron someone said they had taken predicted neither their measured blood level nor their symptoms, so the exposure data here are unreliable.

This concerns routine supplementation in women who are not anaemic, not the treatment of a diagnosed deficiency, where the case is different. The reviewers name the practical consequence themselves: international guidelines on this point disagree with each other. The same review mixes randomised trials with observational studies.

A median is not a person: half of women eat more than 12 milligrams and half less, and falling below a recommendation is not the same as being deficient. These intake figures were compiled for a 2001 report and have not been revised since. The absorption assumptions behind the recommendations predate what is now known about how the body regulates uptake.

People with hereditary haemochromatosis were deliberately left out of the derivation as exceptionally sensitive, so this figure does not protect them. The same 45 milligrams was applied to pregnancy only because data on lower doses in pregnant women did not exist. The chapter was published in 2001 and has not been revised since.

A single blood draw cannot say who felt unwell or who would have benefited from treatment. The headline figure moves with the cutoff chosen, and below 30 is one of several in use. No inflammation adjustment was applied, which by other work would push the estimate higher. The authors say what functional deficiency means in an otherwise well adult is still unresolved.

The pooled fatigue result rests on 4 of the 18 trials, on self-reported scales, and iron is hard to blind because it darkens stool. On the other side, both null trials ran in blood donors, a healthy group whose average fatigue was about 4 out of 10, leaving less room to improve. One of them lasted four weeks, and its own authors note the donation had not made these women noticeably tired.

In people low on iron but not anaemic, iron refills the stores. Whether that eases tiredness is open: pooled trials found people reporting less of it, while two placebo-controlled trials, one refilling stores more fully, found nothing.

Neither source was designed to test the pairing: one is a set of marker outcomes graded very low to moderate certainty, the other an absence noted while setting an intake limit. The child trials used substantial doses of both minerals in populations where deficiency is common, not the amounts in an ordinary multivitamin. And the panel's finding was recorded in 2001 and has not been revisited.

A US panel found no evidence of clinically significant harm from iron and zinc interacting; pooled trials in under-threes saw zinc move iron markers the wrong way. Neither set out to test the pairing, so whether to space them is unknown.