Does biotin work for hair loss? Biotin, zinc and iron

Every October the same thing happens: the brush brings back more hair than it did in July, someone mentions it in the queue at the shop, and a week later there is a pot of biotin in the basket. The awkward part is that the number printed on that pot — 5,000 or 10,000 micrograms — has nothing to do with the amount European law actually needs in order to let it say it looks after your hair. That amount is 7.5 micrograms.

This article is not going to tell you that hair supplements are useless, because that would be as false as the advert. It is going to do something more useful: lay out the six claims the European Union does authorise about hair and nails, the one it refused and why, what the biotin trials have found, and a fact almost nobody mentions: that alopecia is the criterion the EFSA itself uses to set the upper limit for selenium. Same nutrient, same organ, in both directions. Our three shops are in Spain, in Barcelona and Sant Cugat, and the figures in this article are the ones in European law.

In short

More hair really does fall out in autumn, and it is not just an impression. In 823 women followed for six years, the proportion of hair in the resting phase peaked in summer and bottomed out in late winter. That hair is shed weeks later.
The EU authorises six claims about hair and nails, and all of them say «maintain», none says «grow»: biotin, zinc and selenium for normal hair, zinc and selenium for normal nails, and copper for normal hair pigmentation.
The claim «reduces hair loss» was applied for and refused. The application covered biotin and six other vitamins; the only study submitted did not use the product the claim was about.
To be legally allowed to say biotin looks after your hair, 7.5 µg a day is enough. A 10,000 µg pot carries 1,333 times that and buys no extra sentence.
High-dose biotin wrecks blood tests. The FDA — the United States medicines and devices agency — warned in 2017 about interference with troponin and thyroid assays, with one death linked to a falsely low result.
Too much selenium makes hair fall out. In 2023 the EFSA — the European Food Safety Authority — set the upper limit at 255 µg a day using alopecia itself as the criterion, and named high-dose supplements and Brazil nuts as the two ways of going over it.
If you suspect iron, what you need is a ferritin test, not a pot. And it is worth knowing that a study of 381 women found no more iron deficiency in those losing hair than in those who were not.

What actually happens to hair in autumn

Hair does not grow continuously: each follicle alternates a long growth phase with a short resting phase, and at the end of that resting phase the hair lets go and makes room for the next one. A normal scalp has tens of thousands of follicles at different stages, so daily shedding is constant and goes unnoticed. What you notice is a change in proportion: if suddenly more follicles are resting, a few weeks later there is more hair in the brush.

That is exactly what has been measured. Kunz, Seifert and Trüeb reviewed six years of data from 823 women consulting about hair loss, after excluding those with a disease or a drug that would explain it, and found a clean annual cycle: the proportion of hair in the resting phase was highest in summer and lowest in late winter, with a smaller second peak in spring. Because that hair takes weeks to be shed, the complaint arrives in late summer and autumn.

The practical consequence matters and sells nothing: shedding that starts in September, leaves no visible bald patches and fades over a few weeks has the shape of a seasonal phenomenon. Before buying anything, it is worth waiting and watching. What does justify seeing a doctor is something else: bald patches, loss in specific areas, significant itching or flaking, shedding that lasts months, or shedding together with heavy fatigue, weight changes or very heavy periods.

What European law lets you say about hair, and what it refused

In the European Union you cannot attribute any effect you like to a food or a supplement: only authorised health claims count, with their official wording and their condition of use. For hair and nails there are exactly six, listed in Regulation (EU) 432/2012:

“Biotin contributes to the maintenance of normal hair.” “Zinc contributes to the maintenance of normal hair.” “Zinc contributes to the maintenance of normal nails.” “Selenium contributes to the maintenance of normal hair.” “Selenium contributes to the maintenance of normal nails.” “Copper contributes to normal hair pigmentation.”

Read the verb again. All six say maintenance. None says reduce shedding, slow loss or increase density. That is not a drafting slip: that claim was applied for and refused. A company sought authorisation for a combination of thiamin, riboflavin, niacin, pantothenic acid, pyridoxine, D-biotin and pumpkin seed oil with the effects “contributes to reduce hair loss” and “increases the number of hair”. The EFSA concluded that no cause-and-effect relationship had been established, and the technical reason is one worth telling in full: the only publication the applicant submitted did not use the product the claim was about. In the same 2012 opinion a second application was rejected, the one for the preparation KF2BL20, also for the maintenance of normal hair.

The second half of the rule is the one nobody looks at, and it is the one that decides whether a pot qualifies: to use any of the six, the product must be at least a «source of» that nutrient, meaning it supplies 15 % of the reference value — in a supplement, per recommended daily dose. With the values in Regulation (EU) 1169/2011, the arithmetic comes out like this:

Nutrient	What it may say (432/2012)	NRV	Minimum needed to say it (15 %)
Biotin	Maintenance of normal hair	50 µg	7.5 µg
Zinc	Maintenance of normal hair and nails	10 mg	1.5 mg
Selenium	Maintenance of normal hair and nails	55 µg	8.25 µg
Copper	Normal hair pigmentation	1 mg	0.15 mg
Iron	None about hair	14 mg	—
Collagen	None authorised	—	—

The 7.5 µg of biotin is the figure of this article. It is the amount that makes a product legally fit to say it contributes to the maintenance of normal hair. A supplement with 10,000 µg supplies 1,333 times that, and the sentence it is allowed to print on the box is exactly the same. What you paid extra buys not one word.

Look at the last two rows as well. Iron has seven authorised claims — oxygen transport, cognitive function, tiredness, immunity — and none about hair. And collagen, the other big name on the shelf, has no authorised claim for anything at all: its only presence in the European list comes through vitamin C, which contributes to its normal formation. The collagens and cartilage section covers it.

What the evidence says, nutrient by nutrient

Biotin: a lot of noise and a deficiency almost nobody has

Biotin is a B-group vitamin and its role in hair is real: when it is genuinely missing, hair falls out. The question is how many people are in that position. The fact sheet from the Office of Dietary Supplements at the United States National Institutes of Health puts it plainly: the adequate intake for adults is 30 µg a day, a normal Western diet supplies between 35 and 70 µg, and severe biotin deficiency has never been reported in healthy people eating a normal mixed diet. Deficiency does exist in specific situations: biotinidase deficiency, chronic alcohol use, malabsorption.

And supplements in people without a deficiency? A 2026 systematic review gathered ten studies on biotin and hair growth in alopecia and reached a carefully hedged conclusion: biotin on its own showed no consistent benefit on objective growth measures, the single monotherapy trial found no measurable benefit, and the improvements turned up in multi-ingredient combinations, which makes it impossible to credit biotin for them. The authors conclude that current evidence does not support routine supplementation without documented deficiency.

There is one figure in that same review worth knowing because it gets used as a sales argument: in a series of about 541 women, 38 % had blood biotin below 100 ng/l. It sounds alarming until you read the small print: that study had no comparison group, so it does not tell you whether women without hair loss would have given the same percentage. And the telogen effluvium case-control studies that did compare found no difference in biotin between those losing hair and those who were not.

The clincher comes from a 2024 review: of the three studies that met its criteria, one had a subgroup with real deficiency — 22 of 112 patients — and 23 % of the deficient patients reported improvement, against 38 % of those who were not deficient. In other words, the ones who were not short of it improved more. That is the shape a subjective improvement takes when there is no effect behind it.

Iron: ferritin matters, but it is not the default explanation

Iron does have a known relationship with hair through iron deficiency, and it is the first thing worth ruling out when shedding drags on and there are other symptoms. But the causal role is less direct than the story goes. Olsen and colleagues measured ferritin in 381 women with female pattern hair loss or chronic telogen effluvium and in 76 women with no hair loss, and the result runs against intuition: among premenopausal women with hair loss, 12.4 % had ferritin at or below 15 µg/l, against 29.8 % of the controls; at the 40 µg/l threshold, 58.8 % against 72.3 %. There was no significant increase in iron deficiency in either hair-loss group compared with women without hair loss.

The authors themselves add the honest sentence: the effect of correcting iron deficiency on hair loss is not known. That does not make iron irrelevant — iron deficiency needs treating in its own right, whether or not it has anything to do with hair — but it does dismantle the shortcut of buying an iron supplement because hair is falling out. When it really is short and how to find out is in the article on iron and tiredness, with the ferritin thresholds and the safe level of 40 mg a day set by the EFSA.

Zinc: it has a claim, and it has a ceiling

Zinc comes out best on this list: it holds two of the six authorised claims, one for hair and one for nails, and 1.5 mg per daily dose is enough for it to use them. Most hair, skin and nails supplements carry plenty.

Zinc's problem is at the other end. The EFSA puts its tolerable upper level at 25 mg a day — the American value, 40 mg, is looser — and the mechanism of excess is rather pointed in an article about hair: zinc at high, sustained doses competes with copper and ends up causing copper deficiency. And copper is precisely the holder of the sixth claim on the list, the one about normal hair pigmentation. Taking a lot of zinc «for your hair» for months can end up lowering the very nutrient the law links to hair colour. The differences between forms and doses are in the article on zinc or vitamin C.

Selenium: the same nutrient, in both directions

And here is the piece that makes this article something other than a leaflet. Selenium has two authorised claims: it contributes to the maintenance of normal hair and of normal nails. But when the EFSA reviewed in 2023 how much selenium is safe, it had to pick an adverse effect as the criterion for setting the limit, and it picked alopecia, as the earliest and best-established sign of selenium excess.

The numbers are specific: from a large human trial a lowest observed adverse effect level of 330 µg a day was identified, an uncertainty factor of 1.3 was applied, and a tolerable upper limit of 255 µg a day was set for adult men and women, pregnancy and lactation included. The opinion also says who goes over it: European consumers do not reach that limit from food, except regular users of supplements with high daily doses of selenium and regular eaters of Brazil nuts.

Translated to our own shelves: in vitamins and minerals we have a selenium capsule of 200 µg, which is 364 % of the reference value and 78 % of the daily upper limit on its own; and we have two Brazil nut references in dried fruit and nuts, which is literally the other food the opinion names. Anyone who takes the capsule, eats Brazil nuts daily and also carries a hair complex containing selenium is adding up three sources of the same nutrient for a goal — hair — that an excess of that nutrient makes worse. There is no way of telling this that does not go against the sale, and that is exactly why it is worth telling.

Six things you can do this week

1. Give it three weeks before buying anything

If the shedding started in September, there are no bald patches and the hair coming out has a fine white root, the likeliest scenario is the seasonal one measured in the 823 women of the 2009 study. Three weeks of watching costs nothing and stops you crediting a pot with an improvement that was going to happen anyway. Use the time to look at something else: whether hair is thinning evenly all over or one specific area is clearing, because that changes the diagnosis and no supplement fixes it.

2. Look for the % NRV, not the milligrams on the lid

The big number on the packaging tells you nothing on its own; the one with legal and nutritional meaning is the percentage of the reference value. With the table above in front of you, any supplement that reaches 15 % of the NRV for biotin, zinc or selenium can already say everything the law allows about hair. A figure measured in our own catalogue: of the 19 references in hair, skin and nails, only one shows the % NRV on the product page and six give the nutritional values as «not available». That is our problem and we are fixing it, but in the meantime the physical label on the pot does carry it: turn it round.

3. If you suspect iron, ask for a ferritin test

A blood test with ferritin costs less than three months of supplement and answers the real question. If it comes back low, there is something to treat, and the dose that corrects iron deficiency is a medical prescription, not a pot from vitamins and minerals. If it comes back normal, you have just saved the supplement and ruled out the most frequently named cause. While you wait for the result, the free part: keep coffee and tea away from main meals, because tannins sharply reduce the absorption of plant iron. The figures are in the article on iron and tiredness.

4. Cover protein before the micronutrient

Hair is keratin, which is to say protein, and a sustained shortfall of protein shows in hair long before a biotin deficiency, which barely exists. It is the question almost nobody asks before buying a hair complex: am I hitting my ration? Legumes, eggs, canned fish, cheeses and nuts settle that without going near the supplement aisle, and how much you need is worked out in the article on how much protein per day.

5. Do not stack seleniums or zincs

This is what most people do without noticing: a hair complex, a multinutrient and a standalone capsule, all three with zinc and selenium. Add up the labels before you start and stay below 255 µg a day of selenium and 25 mg a day of zinc counting every source, including Brazil nuts if you eat them daily. If you already take a multinutrient that covers both, the hair complex probably adds nothing legally declarable.

6. Tell the lab if you take biotin

In November 2017 the FDA published a safety communication about biotin: at high doses it interferes with immunoassays that use biotin-streptavidin and can give falsely high or falsely low results for troponin, thyroid hormones, parathyroid hormone and vitamin D. This is not theoretical: the agency recorded one death linked to a falsely low troponin result in a patient taking high-dose biotin. The National Institutes of Health fact sheet adds that a single 10 mg dose can interfere with a thyroid test done within the next 24 hours, and describes cases of false hyperthyroidism in people taking between 10 and 300 mg a day. If you take a hair complex and you are having blood drawn, say so. It is free and it prevents a scare or a wrong diagnosis.

What the box says	What it means	What to do at the counter
Biotin 10,000 µg	1,333 times the legal minimum for the claim; 333 times the adequate intake	Check whether a lower version exists: it says the same thing
Selenium 200 µg	364 % of the NRV and 78 % of the daily upper limit	Add up your other sources before adding it
Zinc 25 mg	The entire daily upper limit in one dose	Check you are not repeating it in another pot
«Hair formula», 8 ingredients	The law only allows claims for those reaching 15 % of the NRV	Ask which of the eight get there
Nutritional values «not available»	No way to do the arithmetic on the website	Ask for the physical pot and read the back
«Reduces hair loss»	Claim refused in the EU	Distrust the whole product

The shopping list

If after reading the above it still makes sense to buy something, here is what there is and what each thing is for. The specific complexes live in hair, skin and nails: the biotin gummies with folic acid, zinc and selenium from Aldous, the hyaluronic acid with vitamin C, biotin, zinc and selenium, the vegetable biotin hair formula from ARGALYS, the Active Capilar Plus from Salengei and the hair, nails and skin tablets from Santiveri, plus the silicon balm with biotin from Hubner.

The single nutrients, for anyone who would rather do the arithmetic themselves than buy a blend, are in vitamins and minerals: the biotin complex with zinc, selenium, vitamin D3 and E from Aldous, the zinc bisglycinate from Aldous, the zinc citrate with pumpkin seeds from Solaray, the 200 µg selenium capsule from Viridian — with the warning from the previous section firmly in mind — and, if the blood test justifies it, the Floradix iron and vitamins syrup. The nutritional yeast with vitamin B12 is the cheap way to add B-group vitamins to a plate instead of to a glass of water.

The food part is the one people look at least and the one that holds everything up: protein in legumes, eggs, canned fish and cheeses; zinc and selenium in seeds and nuts, where the Galderic Brazil nuts and the loose Brazil nuts are; antioxidants and vitamin C in vegetables and in an organic basket; omega 3 in fatty acids. And from the outside, the shampoos and personal care products: of the 387 products in that category, 34 are shampoos, so there is plenty to choose from without fragrance or sulfates if the scalp is irritated.

Do you need supplements for your hair?

For most people who notice more hair in the brush in October, no. And that is worth saying in a shop that sells nineteen hair, skin and nail references.

The reasoning is simple. Biotin deficiency, which is the star ingredient, barely exists in healthy people who eat a varied diet. The evidence for supplementing biotin without a deficiency shows no consistent benefit on objectively measured growth. The only claim the EU authorises is about maintenance, not recovery, and the cheapest product on the shelf already meets it. And iron deficiency, which does need ruling out, is no more common in women losing hair than in women who are not.

When does it make sense? When there is a documented deficiency and it needs correcting. When the diet is genuinely limited — a poorly planned vegan diet, malabsorption surgery, a heavy calorie restriction — and a multinutrient acts as a safety net. When the goal is maintenance and you accept that is what it is: maintenance. And when the alternative is leaving protein uncovered, the one nutrient hair is literally made of.

If we had to rank what to spend on first, hair would come fourth: ahead of it come covering protein, ruling out iron deficiency with a blood test, and checking vitamin D if it is October in Barcelona. The hair complex comes after those three, not before.

Four myths worth dismantling

«Biotin makes hair grow.» The EU authorises saying it contributes to maintaining normal hair, and it expressly refused the claim about reducing shedding and increasing the number of hairs. The 2026 systematic review found no consistent benefit from biotin alone on measured growth, and the 2024 review found no study at all demonstrating benefit in healthy people.
«If 5,000 µg work, 10,000 will work better.» The legal minimum for making the claim is 7.5 µg. Above that you gain no sentence, no demonstrated effect, and you do gain a concrete problem: high doses of biotin distort blood tests, with one death recorded by the FDA linked to a falsely low troponin.
«Selenium is good for hair, so more selenium means better hair.» Excess selenium makes hair fall out. So much so that in 2023 the EFSA chose alopecia as the criterion for setting the 255 µg a day limit, and named high-dose supplements and Brazil nuts as the two ways of going over. Both are on our shelves.
«My hair is falling out, I must be short of iron.» You might be, and it is worth ruling out with a ferritin test. But in 381 women with hair loss, iron deficiency was no more frequent than in the 76 women without it: at the 15 µg/l threshold, 12.4 % against 29.8 %. Iron is taken when the blood test asks for it, not when the brush does.

Where to buy hair supplements in Barcelona and Sant Cugat

We have three shops, all three in Spain, and in all three you can do something you cannot do buying online: bring in the pot you already have at home and do the arithmetic from this article at the counter, with the packaging in front of you. Two divisions and a minute: how many micrograms of biotin the daily dose carries against the 7.5 the claim requires, and how much selenium against the 255 of the upper limit. If you are already taking three things, we add them up together before you buy the fourth. Nobody can do that through a product page, least of all when six of our own pages give the nutritional values as «not available».

The addresses: Carrer de Provença 242, 08008 Barcelona, in the Eixample; Carrer de Còrsega 78, 08029 Barcelona, also in the Eixample, near Sants; and Carrer d'Antoni Bell 2, 08174 Sant Cugat del Vallès, in Volpelleres. The phone number is +34 683 118 961 and the email is linverd@linverd.com. If you would rather browse at your own pace, the whole hair, skin and nails range is on the website.

And one thing that can only be offered in person: telling you not to buy. If you bring the pot in and it turns out the multinutrient you already take covers zinc and selenium comfortably, we will say so, even with the hair complex two metres away. It is less profitable in the short run and it is the only reason to come back.

And if what works is a medicine

There is a point at which an organic supermarket has to step aside, and this is it. For androgenetic alopecia — pattern hair loss, the kind that thins specific areas and does not recover on its own — what has demonstrated efficacy is not a food supplement, it is a medicine. Topical 5 % minoxidil is authorised by the Spanish Agency of Medicines and Medical Devices (the AEMPS, Spain's medicines regulator) for exactly that indication: the treatment of moderate hair loss known as androgenetic alopecia, in men. Its own patient leaflet says it is not recommended in women, because of the risk of hypertrichosis, and that it has not been studied in people under 18 or over 65.

That means two things. That if your hair loss is of that kind, the place to deal with it is the clinic and the pharmacy, not our supplement aisle; and that a food product hinting at doing what a medicine does is, on top of exaggerating, breaking the rules. We can help you with protein, with which blood test to ask for, with not overdoing selenium, and with a shampoo that does not irritate your scalp. The rest is not our job and we would rather say so than sell you a pot.

Frequently asked questions

How much biotin should you take a day for hair?

For a product to be legally allowed to say it contributes to the maintenance of normal hair, 7.5 µg per daily dose is enough, 15 % of the 50 µg reference value. The adequate intake for adults is 30 µg and a normal diet supplies between 35 and 70. The 5,000 and 10,000 µg in beauty pots have no backing in the evidence and add no claim.

Is it normal to lose more hair in autumn?

Yes, and it has been measured. In 823 women followed for six years, the proportion of hair in the resting phase was highest in summer and lowest in late winter, with a smaller peak in spring. That hair is shed weeks later, so the loss is noticed in late summer and autumn. If there are no bald patches and it fades within a few weeks, it fits the seasonal pattern.

Can biotin affect a blood test?

Yes. In November 2017 the FDA warned that high-dose biotin interferes with immunoassays and can give falsely high or low results for troponin, thyroid hormones, parathyroid hormone and vitamin D, with one death recorded from a falsely low troponin. A single 10 mg dose can interfere with a thyroid test within the next 24 hours. Always say so before blood is drawn.

Is selenium good or bad for hair?

Both, depending on the amount. The EU authorises saying selenium contributes to the maintenance of normal hair with only 8.25 µg per dose. But in 2023 the EFSA set the tolerable upper limit at 255 µg a day using alopecia — hair loss — as the criterion, from an adverse effect level of 330 µg. Going over produces the opposite of the effect you were after.

Am I short of iron if my hair is falling out?

Not necessarily, and it is worth checking with a ferritin test before supplementing. In a study of 381 women with female pattern hair loss or telogen effluvium and 76 women without hair loss, iron deficiency was no more frequent in those losing hair: at the 15 µg/l threshold, 12.4 % against 29.8 % of the controls. If ferritin comes back low it needs treating, and that dose is a medical prescription.

Does collagen help hair?

It has no authorised health claim in the European Union, for hair or for anything else. The only official mention of collagen in the European list comes through vitamin C, which contributes to its normal formation. If the goal is to supply the protein hair is made of, food does it better and cheaper.

Where can I buy hair 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 (Volpelleres). You can bring in the pot you already take and we will do the two sums from this article together at the counter: micrograms of biotin against the 7.5 of the claim and micrograms of selenium against the 255 of the limit. The phone number is +34 683 118 961.