Iron and tiredness: do you actually need a supplement?

Every autumn it goes the same way. The light changes, the holidays end, the first week of rain arrives and half the country wakes up with no battery. We have a name for the feeling — autumn fatigue — and a name for the fix too: a bottle. This season the most searched-for bottle is iron, because iron sounds like blood, like energy, like something you use up. The question almost nobody asks before buying it is the only one that matters: am I actually short of iron?

The answer comes with numbers, and they are awkward for anyone selling supplements. Iron reduces fatigue measurably, but only in people whose deficiency has been demonstrated by a blood test. In everyone else it does nothing, costs money and upsets the gut. And the dose that genuinely corrects iron deficiency sits well above what a food supplement can or should give you. Here are the figures, the official claims that can actually be used, and what you can change in your shopping this week without going near a pharmacy.

In short

• The European reference is 11 mg a day for men and postmenopausal women and 16 mg a day for menstruating women (EFSA, the European Food Safety Authority, 2015).
• Iron has seven authorised health claims in the EU, including "Iron contributes to the reduction of tiredness and fatigue", and to use them a food must be at least a source of iron.
• In iron deficiency without anaemia, supplementing reduces subjective fatigue (18 trials, 1,170 participants) but does not improve physical capacity (BMJ Open, 2018).
• Without a measured deficiency, taking iron has no particular reason to make you less tired: what does go up is constipation, at 2.07 times the risk (Cochrane, 2016).
• Of the iron in a Western diet, only 10-15 % is haem iron, the kind that absorbs well. The rest depends entirely on what it is eaten with.
• A black tea with your meal can block up to 94 % of the plant iron on that plate. Taken one hour later, half of that damage disappears.
• If you are vegetarian, your iron requirement is 1.8 times higher: the problem is not how much you eat, it is how much you absorb.

What iron does, and why your tiredness may not be its fault

Iron sits at the centre of haemoglobin, the protein that carries oxygen from the lungs to every cell. If iron runs short, less oxygen arrives and the body slows down: that is the tiredness of iron deficiency anaemia, and it is real. But iron is also involved in energy metabolism, cell division and cognitive function, and there is a middle ground that rarely gets discussed: iron deficiency without anaemia. Low stores, haemoglobin still normal, and a fatigue that does not show up on a basic blood count.

That is where the confusion starts. Autumn tiredness has many causes — less daylight, worse sleep, the return to routine, sustained stress — and iron is only one of them. To know whether it is yours you need one number: ferritin, which measures your stores. And even that number is not simple, because the thresholds are not settled. A Spanish review in Medicina Clínica Práctica (2022) lists cut-offs of 15 µg/l in premenopausal women and 30 µg/l in men and postmenopausal women, while also noting that 45 µg/l gives the best balance between sensitivity (85 %) and specificity (92 %). EFSA itself, when working out how much iron we need, used a target of 30 µg/l. Three different figures for the same question, and a supermarket is not the one who settles it.

The second reason is that dietary iron is not one thing but two. Haem iron, from meat and from canned fish or fresh fish, absorbs well and barely cares what else is on the plate. Non-haem iron, from legumes, seeds and vegetables, absorbs poorly and depends completely on its company. And here is the figure that organises the rest of this article: according to the Office of Dietary Supplements fact sheet from the NIH, the United States public health research agency, haem iron is only 10-15 % of the total iron a Western population eats. Most of our iron is precisely the kind we use worst.

How much iron you need a day, according to EFSA

In 2015 EFSA published its dietary reference values. The average requirement is 6 mg/day for adult men and 7 mg/day for menstruating women; the population reference intake, which is the figure that covers almost everyone, rises to 11 mg/day and 16 mg/day respectively. Postmenopausal women go back to 11 mg. Those numbers are not arbitrary: EFSA assumes we absorb 16 % of dietary iron (18 % in premenopausal women) and aims to keep ferritin at 30 µg/l.

The label will not show you those figures; it shows a different one. The European nutrient reference value for iron is 14 mg (Annex XIII of Regulation 1169/2011), and that is what the percentages on the pack are calculated from. A food can be called a "source of iron" when it provides at least 15 % of that value, which is 2.1 mg per 100 g. This is worth knowing, because the most quoted iron table on the internet, the NIH one, uses a Daily Value of 18 mg, the American figure. Same foods, different percentages. Nobody has made a mistake: there are two regulators.

How much protein and how much fibre you need are neighbouring questions, and we gave each its own article: how much protein per day you really need and how to reach 25 g of fibre. With iron there is one important difference: here, how much you eat matters less than how much you absorb.

What the trials say, without decoration

Two reviews map the ground. The 2016 Cochrane review pooled 67 trials and 8,506 menstruating women: daily iron reduced the risk of anaemia (RR 0.39), reduced the risk of iron deficiency (RR 0.62, in 7 studies and 1,088 women) and raised haemoglobin with high-quality evidence across 51 studies and 6,861 women. It also measured the other side: loose stools or diarrhoea at 2.13 times the risk, and constipation at 2.07 times the risk, both high-quality evidence. Iron works and iron bothers, and both facts are equally well documented.

The second review is the one that really answers the autumn question. A systematic review published in BMJ Open in 2018 looked at adults with iron deficiency but no anaemia: 18 trials and 1,170 participants. On fatigue, iron clearly won — standardised mean difference of −0.38 (95 % CI −0.52 to −0.23) across 4 trials and 714 participants. On physical capacity measured by VO₂ max, nothing happened: 0.11 (95 % CI −0.15 to 0.37) across 9 trials. The authors' conclusion is literal: iron is associated with reduced subjective fatigue but not with objective improvements in physical capacity.

Translated to the shelf: if your stores are low, iron may well make you feel better. If they are not low, those trials do not include you. And if what you want is to perform better at the gym, iron is not your supplement; for the ones that do have data, see our article on magnesium and the one on ashwagandha and cortisol.

Six things you can change this week

1. Measure before you buy

This is the advice that costs us sales and the only honest one. Ask your doctor for a blood count with ferritin before you start on any bottle from the vitamins and minerals aisle. Without that number, taking iron is a bet: you may be correcting a real deficiency, or you may be paying for constipation. And if ferritin does come back low, the dose that corrects it — in Spain the usual course is 100-200 mg of elemental iron a day for 3 to 6 months — is not a job for a food supplement, it is a medical prescription.

2. Put vitamin C in the same meal, not another one

Ascorbic acid is the most effective enhancer of non-haem iron, and it has to be on the same plate. A citrus fruit from the fruit aisle, a tomato, a raw pepper or a handful of parsley next to the lentils does more for your iron than the bottle does. Raw seasonal vegetables are the cheapest route, and we have already written about vitamin C and its limits in zinc or vitamin C for immunity.

3. Move the tea and coffee an hour away

This is the easiest change to make and the most widely ignored. The polyphenols in coffee and teas and in cocoa block the plant iron of the meal they coincide with. You do not have to give anything up: you just move the time. A stable-isotope trial in 12 women, published in The American Journal of Clinical Nutrition (2017), measured absorption of 3.6 % with tea during the meal against 5.7 % when the tea came one hour later, identical to the water control (p = 0.046). Inhibition fell from 37.2 % to 18.1 % purely by waiting.

4. Use the 50-gram fish rule

This is the only authorised EU claim that talks about real food rather than capsules: "Meat or fish contributes to the improvement of iron absorption when eaten with other foods containing iron". Its condition of use is very specific: the effect is obtained by consuming 50 g of meat or fish together with foods containing non-haem iron. A tin of sardines in extra virgin olive oil or of melva — frigate mackerel, a small tuna very common on the Spanish coast — holds 195 g, nearly four times what the rule requires. Half a tin over a lentil salad and you are inside it.

5. Soak, cook and ferment the legumes

The phytates in legumes and wholegrain cereals are the main brake on plant iron, and they come down with long soaking, cooking and fermentation. Loose pardina lentils soaked for twelve hours are not the same food as lentils from a jar. Red lentils, which collapse in twenty minutes, and local pedrosillano chickpeas are the two easiest ways in. If the goal is both iron and fibre, the route is in our article on fibre.

6. If you do not eat meat, count 1.8 times more

This is not an opinion: the NIH put the iron requirement of someone on a vegetarian diet at 1.8 times the usual, because absorption drops from 14-18 % on a mixed diet to 5-12 %. The answer is not to eat twice the lentils, it is to improve absorption using points 2, 3 and 5 and to keep an eye on B12 as well, which is another story and another cause of tiredness. Nutritional yeast with vitamin B12 and B12 as methylcobalamin cover that flank, and the superfoods aisle has more options.

How much iron each drink blocks

These figures come from a classic study by Hurrell, Reddy and Cook in the British Journal of Nutrition (1999), which measured non-haem iron absorption from a bread meal served with different drinks. They are inhibition percentages: how much iron you stop absorbing.

The same study gives the general rule: a drink carrying 20-50 mg of polyphenols per serving reduces absorption by 50-70 %, and one carrying 100-400 mg reduces it by 60-90 %. None of this means giving up tea or cocoa, which have their own merits. It means not drinking them with the plate of lentils.

What to do in your case

The shopping list

Food first. Legumes hold the bulk of plant iron: loose pardina lentils, loose red lentils and loose local pedrosillano chickpeas, which also let you weigh out exactly what you are going to cook. Among seeds, loose pumpkin seeds and loose sesame seeds are the two densest, and they work well scattered over the finished dish. Dried fruit and nuts round out the group, and we covered what counts as a sensible portion in how many walnuts a day.

For haem iron and the 50-gram rule, the canned fish aisle: sardines and melva in extra virgin olive oil are the two tins that go best with a plate of pulses. Eggs and the refrigerated aisle cover the everyday, and in precooked there is tempeh and there are fermented foods that help by another route, by lowering phytates.

To go alongside without getting in the way: seasonal fruit and raw vegetables in the same meal; dark chocolate and coffee and teas, better an hour later. In cereals, bars and muesli it pays to read the label: many declare added iron, and there the percentage on the pack is genuinely useful. Seaweed and superfoods appear on every iron list on the internet, but their iron is non-haem and the same rules apply.

And if, after the blood test, supplementing is the right call, this is what the vitamins and minerals aisle holds: Floradix iron and vitamins syrup, Solaray's iron bisglycinate in tablet form and Floradix Kids, which should not leave the shelf unless a paediatrician has said so. If you would rather not think about the basket, the organic baskets and this week's offers are the shortcut, and the rest is in the pantry.

Do you need iron supplements?

For most of the people who walk into the shop in October saying they are tired, no. And this is the part where a supermarket has to say something an online pharmacy with a sales target never says: iron is the supplement you least want to take blind, for three specific reasons.

The first is that the body has no quick route for getting rid of iron it does not need. The second is dose: in 2024 EFSA reviewed iron and could not establish a tolerable upper intake level for lack of solid data on liver toxicity; instead it set a safe level of total intake of 40 mg a day for adults, including pregnant and breastfeeding women, and derived it from something as unglamorous as the appearance of black stools, which signal unabsorbed iron in the gut. Compare that with the 100-200 mg a day used to treat a real deficiency and the problem is plain: the dose that cures is above what is considered safe for the general population. That is not fixed with a bottle, it is fixed with a doctor.

The third is safety at home. The NIH record gastrointestinal effects — nausea, constipation — from 45 mg a day, corrosive necrosis of the intestine above 20 mg per kilo and, the figure that changes the conversation, at least 43 children dead in the United States between 1983 and 2000 from iron supplement overdose. We sell Floradix Kids and we say it anyway: a children's iron supplement is a medicine in all but name and should be stored like one, out of reach and with a paediatrician in the loop.

What does make sense to buy without a blood test is food. A plate of loose lentils with half a tin of sardines and a tomato is the cheapest, safest and best documented intervention in this whole article. If your problem is digestive rather than about iron, the digestive system aisle and what we explain in which probiotic to take are a better starting point than a bottle of iron.

The four iron myths

"I'm tired, I'll take iron." It only works if there is a deficiency. The BMJ Open trials selected people with demonstrated iron deficiency; outside that group there are no data supporting less tiredness, and there are data showing more constipation.

"Lentils have more iron than meat." Per 100 grams dry, the legume figure is striking, but their iron is non-haem and absorbs at 5-12 % against 14-18 % on a mixed diet. The amount on the label and the iron that reaches your blood are not the same number.

"Iron gives you energy to train." In deficiency without anaemia, VO₂ max did not improve significantly across 9 trials. Iron corrects a shortfall; it is not an ergogenic aid.

"More milligrams, better." Gastrointestinal effects start at 45 mg a day, and the level EFSA considers safe is 40 mg a day counting everything you eat. The same reasoning we applied to zinc.

Where to buy iron and iron-rich food in Barcelona and Sant Cugat

All three of our shops carry the vitamins and minerals section and, more to the point for this subject, loose legumes and seeds:

• Provença 242, 08008 Barcelona — Eixample district, between Enric Granados and Balmes.
• Còrsega 78, 08029 Barcelona — Eixample, close to Sants station.
• Antoni Bell 2, 08174 Sant Cugat del Vallès — Volpelleres neighbourhood.

You can call us on +34 683 118 961 or write to linverd@linverd.com before coming, to find out which iron products each shop has in stock, because they do not always match.

And here is what a search engine cannot do for you. In the shop you can turn the bottle round and look for two things on the label: the milligrams of elemental iron per dose and the percentage of the reference value. A pack advertising "iron complex 300 mg" is not telling you how much iron you are holding, in exactly the way "500 mg of enzyme complex" was not a dose when we wrote about enzymes and probiotics. If the bottle does not state it clearly, our recommendation is to leave it on the shelf. And if you tell us you are tired and have had no blood test, what we are going to offer you is not the bottle: we will weigh out half a kilo of pardina lentils, put a tin of melva next to it and tell you to have your after-lunch coffee an hour later. It is a smaller receipt and better advice.

Frequently asked questions

How much iron do I need a day?

The European reference from EFSA is 11 mg a day for adult men and postmenopausal women, and 16 mg a day for menstruating women. The average requirement is lower — 6 and 7 mg — because the population reference intake is set to cover almost everyone. Food labels, meanwhile, use a reference value of 14 mg.

Can I take iron without a blood test?

It is not a good idea. Iron reduces fatigue in people with a demonstrated deficiency, but in anyone without one it only delivers gut effects: Cochrane measured constipation at 2.07 times the risk. Ask for a ferritin test before buying any iron supplement.

Which Linverd foods have the most iron?

Loose legumes, pumpkin seeds and sesame among the seeds, and canned fish for haem iron. Leafy vegetables do contribute, but their iron is non-haem and depends heavily on what you eat it with.

Do coffee and tea really take iron away?

They block absorption of the plant iron in the meal they coincide with. Black tea reduced it by 79-94 % in the study by Hurrell and colleagues (1999). The answer is not to give them up: in a 2017 trial, simply drinking the tea an hour after the meal brought absorption back to the level of the water control.

Where can I buy iron supplements in Barcelona or Sant Cugat?

In our three shops — Provença 242 and Còrsega 78 in Barcelona, and Antoni Bell 2 in Sant Cugat del Vallès — and in the vitamins and minerals section of the online shop. You can call +34 683 118 961 to check which products each shop has before travelling.

I am vegetarian, do I need an iron supplement?

Not necessarily, but you do need more iron: the NIH put the requirement at 1.8 times that of a mixed diet, because absorption falls from 14-18 % to 5-12 %. The first step is improving absorption — vitamin C in the same meal, tea and coffee separately, soaking the pulses — and keeping an eye on vitamin B12, which causes a similar kind of tiredness.

Can I give my children iron if they seem tired?

Not without a paediatrician. Iron supplements are a recognised cause of serious accidental poisoning in small children: the NIH record at least 43 child deaths in the United States between 1983 and 2000. Floradix Kids exists and we sell it, but it is a product to use on medical advice and to store out of reach.

To finish

Iron is one of the few supplements where the right answer starts with a blood test and not with a shelf. If ferritin comes back low, there is a treatment and it works. If it comes back fine, your October tiredness has another explanation and you will find it faster in your sleep schedule than in a bottle. In the meantime, food needs no permission: loose legumes, seeds on top, some canned fish alongside and the coffee an hour later.

Come by Provença 242 or Còrsega 78 in Barcelona, or Antoni Bell 2 in Sant Cugat del Vallès, or browse the pantry and the offers in the online shop. If you want to keep reading, the health blog has two articles that pair with this one: how much protein per day you really need, because the other autumn mistake is confusing tiredness with lack of muscle, and omega 3: how much EPA and DHA per day, the other case where the label does not say what it looks like it says.

This information is for general guidance and does not replace advice from a health professional. Iron deficiency is diagnosed with a blood test and its treatment must be prescribed by a doctor. If you are pregnant or breastfeeding, taking medication, or living with a digestive, liver or blood disorder, seek medical advice before taking any iron supplement. Iron supplements must be stored out of the reach of children.