A tub of hair vitamins runs to 25 euros at the chemist. I turned one over and added up the biotin: 10,000 micrograms per capsule.
The Dutch Voedingscentrum works with a daily need of around 40 micrograms for adults. So that tub sits more than two hundred times above it.
The entire Dutch top 10 for this question consists of parties who sell vitamins. They all reach the same conclusion, which is precisely why I believe little of it.
My position: vitamins do something if you are deficient, and almost nothing beyond that. With two nutrients, too much is a known cause of hair loss.
Which vitamin deficiency causes hair loss?
The clearest candidates are iron, vitamin D and vitamin B12. With a genuine deficiency these can go together with diffuse hair shedding, meaning thinner hair across your whole scalp. Zinc belongs in theory, but zinc deficiency is rare in the Netherlands. A review of vitamins and minerals in hair loss calls the evidence mixed and asks for larger studies (Almohanna, 2019).
Note the word deficiency. That is not the same as a value at the bottom of the reference range.
This is how I read the state of play per nutrient.
| Nutrient | What the evidence shows | Worth supplementing? |
|---|---|---|
| Iron and ferritin | Strongest signal in diffuse loss, evidence still mixed | Yes with a proven deficiency |
| Vitamin D | Often measured lower in hair loss, cause unclear | Yes if deficient, certainly in winter |
| Vitamin B12 | Relevant with little or no animal produce | Yes with a proven deficiency |
| Zinc | Deficiency is rare in the Netherlands | Only with a proven deficiency |
| Biotin | Deficiency is very rare, effect without one barely supported | Rarely, and it disturbs blood tests |
| Selenium | Too much is a known cause of hair loss | No, without a proven deficiency |
| Vitamin A | Too much is linked to hair loss | No, without a proven deficiency |
You will not find those last two rows on any sales page. They are the most interesting ones, because they flip the logic.
Does biotin help against hair loss?
With a genuine biotin deficiency yes, but that barely occurs. Biotin sits in eggs, nuts, pulses and wholegrain products, and your gut bacteria make some themselves. For healthy men without a deficiency there is little evidence that extra biotin thickens hair. The high doses in hair supplements are mostly marketing.
There is also a concrete downside, and this is the part of the story you will not read elsewhere.
Many laboratory assays use biotin in the measuring reaction. Take high doses and your result can skew without anyone noticing.
In a JAMA study, healthy adults took 10 mg of biotin a day. The researchers explicitly call that a dose common in over-the-counter supplements, and several hormone assays went off afterwards (Li, 2017).
Thyroid values, hormones and even cardiac markers can be affected (Luong, 2019). The advice from that same review is simple: stop at least 48 hours before the draw.
Picture two men who both take 10 mg of biotin a day for their hair loss.
One never has blood drawn and notices nothing. The other has his thyroid checked after three months, gets an abnormal TSH back, and spends months chasing a problem that is not there.
Same tub, very different story. What goes wrong is covered in hair loss and your thyroid.
Can vitamin B12 cause hair loss?
A marked B12 deficiency can go together with hair loss, usually as part of a broader picture with fatigue, tingling in hands or feet and pallor. B12 plays a role in making red blood cells, and those carry oxygen to your hair roots. The risk is highest in men who eat little or no animal produce.
If you take acid reducers or metformin long term, B12 is a fair question for your GP too.
What a deficiency does further, and which symptoms men tend to wave away, is in vitamin B12 deficiency in men.
What matters is that B12 is rarely the only explanation. With a receding hairline it is almost never the answer.
What about iron and ferritin?
Of all nutrients, iron has the strongest link with diffuse hair shedding. Ferritin shows your iron stores and can already be low while your haemoglobin is still fine. Even so the evidence is not as hard as supplement pages suggest: a review in the JAAD found insufficient grounds to screen everyone with hair loss for iron deficiency as standard (Trost, 2006).
So why do I still name it first?
Because in diffuse loss it is one of the few things you can act on, and because a low ferritin in men raises questions anyway. Men do not lose blood monthly.
A low ferritin in a man is therefore never simply a diet problem. It belongs in a conversation with your GP, even if your hair was the reason you looked. We explain that in iron deficiency in men.
Starting iron on your own is a poor plan. Excess iron accumulates, and that is not harmless.
Does vitamin D work against hair loss?
People with hair loss more often have a lower vitamin D value in studies, but whether that is the cause nobody knows for sure. Topping up a proven deficiency is sensible for other reasons, like your bones and muscles. Do not expect a thick head of hair from it.
In the Netherlands a low value in winter is ordinary. The Gezondheidsraad therefore advises extra vitamin D for certain groups anyway.
What a deficiency does in men is in vitamin D deficiency in men. And which supplements for men genuinely hold up is weighed in supplements for men.
What you can do now
Measure before you swallow. That is the whole message of this piece, and it saves you a drawer full of half-empty tubs.
If you currently use a hair supplement with high-dose biotin, leave it for at least two days before a blood draw and tell your doctor you take it.
If you want ferritin, vitamin D and B12 looked at in one go, they sit in our extended health checkup. If everything comes back normal, you know to look elsewhere for the answer, and that is worth something too.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
References
- Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The role of vitamins and minerals in hair loss: a review. Dermatol Ther (Heidelb). 2019. PMID 30547302.
- Trost LB, Bergfeld WF, Calogeras E. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. J Am Acad Dermatol. 2006. PMID 16635664.
- Li D, Radulescu A, Shrestha RT, et al. Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults. JAMA. 2017. PMID 28973622.
- Luong JHT, Male KB, Glennon JD. Biotin interference in immunoassays based on biotin-strept(avidin) chemistry: an emerging threat. Biotechnol Adv. 2019. PMID 30872068.
- Ylli D, Soldin SJ, Stolze B, et al. Biotin interference in assays for thyroid hormones, thyrotropin and thyroglobulin. Thyroid. 2021. PMID 34042535.
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