Iron Supplements for Tiredness in 2026: The 40-Woman Trial Behind Every-Other-Day Dosing, the Ferritin Number GPs Argue Over – and Who Should Get a Blood Test First

Forty women in Zurich, sixty milligrams of iron and a blood test every morning. That’s the entire evidence base behind the “take your iron every other day” advice that has been doing the rounds on British TikTok since about March, and it’s better evidence than most supplement trends get. But it also isn’t quite what the videos say it is, and it has nothing to say about whether you need iron in the first place. If you’ve been searching for iron supplements for tiredness this month – and September is when the searches climb, as the school run restarts and the light starts going at half seven – the honest position is more useful than the hype: the pills work if you’re low, they do nothing if you aren’t, and the only way to know which camp you’re in costs a GP appointment rather than £9 in Boots.

I’ve spent two weeks reading the trials, the NHS guidance and the British Society for Haematology’s laboratory guideline, and I’ve come away with an opinion that won’t please the supplement aisle. Most of the people buying iron in autumn shouldn’t be buying it blind. And some of the people who most need it are the ones who’ve decided a gentle liquid sachet will do.

Iron supplements for tiredness: the ferritin number GPs still argue over

Start with the bit that confuses everyone, including a fair few doctors. There are two separate things a blood test looks at. Haemoglobin tells you whether you’re anaemic – below 120 g/L for women, 130 for men. Ferritin tells you how much iron you’ve got in storage, and it’s the number that matters for tiredness, because you can run your stores right down long before your haemoglobin drops.

The problem’s the cut-off. The World Health Organization calls ferritin below 15 µg/L deficient. The British Society for Haematology’s 2021 laboratory guideline says below 30 is the sensible line for iron deficiency in adults, whether or not you’re anaemic. A 2025 paper in The Lancet Global Health argued the physiological threshold – the point at which your body starts behaving as if it’s short – is higher still. So a woman with a ferritin of 22 can be told she’s “in range” by one lab print-out and “iron deficient” by a haematologist reading the same sheet.

That gap is where a lot of autumn tiredness lives.

The scale of it in Britain isn’t small. The National Diet and Nutrition Survey found 30% of 11 to 18 year olds and 14% of adults aged 19 to 64 eating less iron than the Lower Reference Nutrient Intake, which is the amount only the 2.5% of people with the very lowest needs can get away with. Nine per cent of teenage girls and 5% of women aged 19 to 64 had both haemoglobin and ferritin below the WHO thresholds – which, remember, are the lenient ones. Use the BSH line instead and the number of women walking around iron-short is comfortably higher. A review in Clinical Medicine put iron deficiency without anaemia at “at least twice as common” as the anaemic version worldwide, and called it poorly recognised in primary care.

And that’s the group who type “iron supplements for tiredness” into Google at 11pm: not anaemic, not ill, just knackered in a way that sleep doesn’t fix.

What 40 women in Zurich taught the internet about every-other-day dosing

The alternate-day advice comes from a pair of open-label trials by Nicole Stoffel’s group at ETH Zurich, published in The Lancet Haematology in 2017. In the first, 40 iron-depleted women took 60mg of iron as ferrous sulfate either every morning for 14 days, or every other morning for 28 days. Same total dose. The researchers labelled the iron with stable isotopes, so they could measure exactly how much of each dose ended up in red blood cells rather than in the toilet.

The alternate-day group absorbed 21.8% of what they swallowed. The daily group absorbed 16.3%. In total iron that’s 175mg banked against 131mg – roughly a third more, from the same number of tablets.

The mechanism is the interesting part, and it’s why this isn’t just another supplement fad. Your gut controls iron uptake with a hormone called hepcidin. Take a decent dose of iron and hepcidin spikes within hours, then takes about a day to settle. Take another tablet while it’s still raised and the door is half shut – a lot of the second dose simply doesn’t get in. Skip a day and the door’s open again. The Zurich team measured hepcidin daily and found it sat higher in the every-day group for the whole first fortnight.

So far, so TikTok. Here’s what the videos leave out.

A 2023 double-blind trial in eClinicalMedicine, with the same total dose, found alternate-day dosing didn’t produce higher ferritin at the end – it produced fewer women still deficient at six months and fewer stomach complaints. And a small 2025 pilot in young women with iron deficiency found daily dosing improved haemoglobin faster. Read together, the picture is: every other day is easier on your gut and wastes less iron, but if you’re properly anaemic and your GP wants your haemoglobin up quickly, daily is still what they’ll prescribe, and they’re not being old-fashioned. Absorbing 30% more of each tablet isn’t the same as getting there in half the time.

The other catch is that the Zurich dose was 60mg of elemental iron. That’s roughly one NHS-strength ferrous sulfate 200mg tablet, which contains 65mg. It isn’t a Spatone sachet (5mg) or a “gentle iron” gummy (usually 7 to 14mg). Alternate-day dosing works because the dose is big enough to trigger hepcidin in the first place. Taking a 14mg tablet every other day isn’t a hack. It’s just taking very little iron.

Does topping up iron actually fix tiredness if you’re not anaemic?

This is the question that matters, and the answer is a qualified yes – with the qualification doing a lot of work.

The best summary is a 2018 systematic review in BMJ Open by Houston and colleagues, which pooled randomised trials of iron – oral, injected or intravenous – in adults who were iron deficient but not anaemic. The finding: iron reduced self-reported fatigue, but didn’t improve objectively measured physical capacity. People felt less tired. They didn’t run any faster on a treadmill.

Sceptics read that as placebo. I don’t, quite. The fatigue scales used in these trials are the same ones used to judge antidepressants and chemotherapy side effects; “I feel less wiped out” is the outcome most people are paying for. And the largest trial in that review – 198 French women with ferritin under 50 and unexplained tiredness, published in the CMAJ in 2012 – gave 80mg of iron a day for 12 weeks and found fatigue scores fell by about half compared with a third on placebo. Not a miracle. A real, modest difference in women who were low to begin with.

But note the entry criteria. Every one of those trials picked women whose ferritin was already low. There’s no trial – none – showing that iron does anything for tiredness in someone whose stores are fine. That’s not a gap in the research. It’s the biology: if hepcidin sees plenty in the tank, it shuts the door, and the tablet passes through doing nothing except possibly upsetting your stomach.

This site looked at something similar with vitamin D last month: a supplement that helps the deficient and does nothing measurable for anyone else. Iron is the same story with a nastier side-effect profile.

Spatone, Floradix or the box from behind the pharmacy counter

Walk into any Boots and the iron shelf runs from about £2.50 to £14, and the price is close to inversely related to how much iron you’re getting.

At the cheap end, own-brand ferrous fumarate or “iron 14mg” tablets – a month’s supply for the price of a meal deal. Fourteen milligrams is the EU reference intake, and it’s a maintenance dose, not a treatment dose. It’s fine if your diet is a bit short and you want a top-up. It won’t move a ferritin of 12.

Spatone is the sachet of Welsh spa water that’s been on the shelves since the nineties, and it’s the one my sister-in-law swears by because it doesn’t make her constipated. It doesn’t make anyone constipated, because a sachet contains 5mg of iron. The absorption is decent – the brand’s own studies suggest around 40% of a very small number – but you’d need a dozen sachets to match one prescription tablet. At around £10 for 28, it’s a pleasant, expensive way to do very little. If your ferritin is actually low, skip it.

Floradix and the other liquid tonics sit in the middle: about 10mg per 10ml dose, roughly £12 a bottle, well tolerated, and again mostly a maintenance product dressed up as a treatment.

Then there’s the box the pharmacist keeps behind the counter. Ferrous sulfate 200mg is a pharmacy medicine in Britain, not a prescription-only one, so you can ask for it. One tablet gives you 65mg of elemental iron – the dose that the Zurich trials, the French fatigue trial and the NHS treatment guidance all use. It costs a couple of pounds for 28. It will, in about a quarter of people, cause constipation or nausea. And it’s far and away the best value if you’ve been told you’re low.

The gummies and “gentle” bisglycinate capsules at £15 to £20 a pot are the ones I’d leave. Bisglycinate is probably slightly better absorbed than sulfate at equivalent doses – the evidence is thin and mostly industry-funded – but the doses in the pretty packaging are usually 14 to 25mg, which puts them in the maintenance category at four times the price. And gummies, as the site found when it looked at creatine gummies in August, have a habit of testing at a fraction of what’s on the label.

Five people who should get a blood test before buying anything

The NHS position is simple and I think correct: don’t take iron for tiredness without a test. A full blood count and ferritin is a standard GP request, it’s free, and it takes a week. Here’s who should book it now rather than guess.

Women with heavy periods. This is the single biggest cause of iron deficiency in Britain and the most under-treated. If you’re changing protection every couple of hours, flooding overnight, or your period regularly runs past seven days, you’re losing more iron than a normal diet replaces. A lot of women assume heavy is just what theirs are like. Get the ferritin done, and ask about the periods too.

Anyone who’s just started running or gym training seriously. The autumn intake – Couch to 5K, the Hyrox sign-ups, the “get fit before Christmas” crowd. Exercise raises hepcidin for hours afterwards, hard training increases losses through sweat and the gut, and endurance running actually breaks red blood cells in the feet. The step-count piece from earlier this month made the case that a 7,000-step walk is enough for most health outcomes; if you’ve gone well beyond that and you’re inexplicably flat, iron is the first thing to check.

Vegetarians and vegans, above all women under 50. Plant iron is absorbed at roughly a third to half the rate of iron from meat, and tea and coffee with meals cut it further. The NDNS data shows the intake gap; the anaemia figures show it converting into real deficiency in a minority. Not everyone. Enough to be worth a test.

Blood donors. A single donation removes about 200 to 250mg of iron – more than a month’s absorption for most women. NHS Blood and Transplant screens haemoglobin before every donation, but it doesn’t check ferritin, and it’s entirely possible to pass the finger-prick and still have almost nothing in storage. If you donate three or four times a year and feel worse each time, this is why.

Anyone over 50 with new tiredness and no obvious cause. This is the one where self-treating is a mistake with consequences. Iron deficiency in a man of any age, or a woman past the menopause, isn’t a diet problem until proven otherwise – the NHS guidance is that it needs investigating for bleeding in the gut. Taking a tablet from the pharmacy might make you feel better for a few months and delay a conversation that shouldn’t be delayed.

And a sixth, the other way round: if anyone in your family has genetic haemochromatosis – Haemochromatosis UK puts the condition at around one in 150 people, more in those with Irish or Scottish ancestry – don’t take iron at all until you’ve been tested. Iron overload does slow, quiet damage to the liver and joints and there’s no upside to guessing wrong.

What I’d do this autumn

If your ferritin comes back under 30, ask for ferrous sulfate 200mg and take one tablet every other morning with a glass of orange juice and nothing else for an hour. The NHS label still says once a day, and if your GP wants daily because you’re anaemic, do daily. Either way, give it three months before re-testing. The NHS says most people notice a difference in three to four weeks; the stores take longer to refill. If the every-other-day version still upsets your stomach, take it with food – you’ll lose some absorption, but a tablet you actually take beats one you don’t.

Keep tea and coffee at least an hour away from the tablet. Same with calcium, so not with your cereal and milk. This isn’t folklore; the tannins and calcium bind iron in the gut, and the effect is large enough to show up in the isotope studies.

If your ferritin is between 30 and 50, you’re in the zone where the trials found a modest benefit for tiredness but where a GP might reasonably say you’re fine. My view: try three months of a proper dose, every other day, and see if it changes anything. If it doesn’t, stop. The tiredness is coming from somewhere else – the flu piece last week made the point that a lot of September exhaustion is just the first term’s worth of viruses arriving at once.

If it’s over 50 and you’re still tired, put the iron down. The money’s better spent on almost anything else, including an earlier night.

And whatever the number, don’t go past 65mg a day without a doctor telling you to. Iron is one of the few supplements where the overdose is real – a handful of adult tablets can seriously harm a small child, which is why the NHS tells you to keep it well out of reach – and the gut side effects rise steeply with dose without absorption rising to match.

The bit the supplement shelf doesn’t tell you

Iron is unusual among the pills British women buy in autumn: it has trial evidence for the exact symptom people take it for, and it’s cheap. That should make it the easy one. It isn’t, because the products with the marketing budgets are the low-dose, well-tolerated, expensive ones, and the product that actually works is a plain white box that costs less than a coffee and makes some people feel a bit sick.

The every-other-day trick is real, and it’s worth knowing. But it’s a way of taking a proper dose more comfortably, not a way of making a token dose count.

So the question I’d put back to you, if you’ve got a half-used tub of iron gummies in the kitchen cupboard: do you actually know your ferritin number – or did the tiredness just seem like reason enough?