Which vitamin deficiency causes hair loss and when should you test your blood?

An iron deficiency is the best-known nutritional cause of hair loss, and low vitamin D levels are also regularly linked to it. The evidence is much weaker for vitamin B12, folic acid, zinc and biotin. A large overview study concludes that supplementation is especially useful if a blood test really shows a deficiency^[1]. Taking too much can even be counterproductive: an overdose of vitamin A or selenium can actually cause hair loss. If you lose more hair than normal, first have your doctor find out what is going on^[2], instead of taking the gamble and buying a jar of vitamins.

In this article

• Which vitamin deficiency causes hair loss?
• What does the research say per nutrient?
• Can a vitamin D deficiency cause hair loss? cause?
• Does biotin help against hair loss?
• Can too many vitamins cause hair loss?
• When should you have your blood tested?
• What if your blood values are good?
• Frequently asked questions
• Sources

Which vitamin deficiency causes hair loss?

Strictly speaking, iron is not a vitamin but a mineral, yet it is the nutrient with the strongest link to hair loss. Thuisarts.nl mentions "too little iron in your body" in addition to stress, fever, being very thin and childbirth as a possible cause of temporary hair loss^[2]. According to the review study by Almohanna and colleagues in Dermatology and Therapy, most researchers agree that you should supplement with iron if someone with hair loss has an iron deficiency or low ferritin^[1]. There is no agreement yet about exactly what ferritin value is "normal" for your hair. You can read more about this in our blog about hair loss due to iron deficiency.

Vitamin D comes next. With other vitamins and minerals the connection is uncertain or only seen in small studies. That does not mean that they are unimportant for your body, but that a supplement usually does not save your hair if you are not deficient.

What does the research say per nutrient?

The table below summarizes what the overview study concludes per nutrient for the two most common forms of hair loss: temporary diffuse hair loss (telogen effluvium) and hereditary hair loss^[1].

Note: this is an overview of often small studies. The authors themselves write that large, well-designed studies are needed to know for sure whether supplementation really helps the hair^[1].

Can a vitamin D deficiency cause hair loss?

The connection is clearest with alopecia areata, the form in which you suddenly develop round bald spots. Several studies found low vitamin D levels more often in these people. With normal diffuse or hereditary hair loss, the results vary. Most researchers recommend supplementing with vitamin D if you lose hair and have a deficiency^[1].

Apart from your hair, the Nutrition Center has fixed advice for certain groups^[3]:

If you belong to such a group, then this advice is a good starting point. You should only take a higher dose in consultation with your doctor. And if you get bald spots, that is a reason to go to the doctor^[2]. Minoxidil is not the first step there.

Does biotin help against hair loss?

Biotin (vitamin B8, also called B7 or vitamin H) is contained in many hair supplements, but a deficiency is rare in people who eat normally. The review study found no good evidence that extra biotin promotes hair growth, and concludes that healthy people do not need to supplement^[1]. Only in rare situations with a real deficiency did doctors see improvement.

There is also a practical risk. According to the US FDA, biotin may interfere with some laboratory tests, including tests used to diagnose a heart attack. As a result, a result can be wrongly too high or too low^[4]. If you take a supplement with biotin, always tell your doctor or the lab before having your blood taken.

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Can too many vitamins cause hair loss?

Yes. More is not always better. According to the overview study, too much vitamin A, for example due to long-term high doses from supplements, can cause hair loss. With selenium, an intake of more than 400 micrograms per day can be toxic, with symptoms including brittle nails and hair loss^[1]. If you combine multiple supplements, such as a multivitamin, a hair supplement and individual capsules, add the quantities on the label together. If you are in doubt, ask your pharmacist.

When should you have your blood tested?

Thuisarts.nl recommends making an appointment if you are losing more hair than normal, your hair is thinning, you suddenly develop bald spots, or if you are concerned or feel insecure about your hair loss^[2]. The GP looks at your complaints, your diet, recent illness, stress and medication use, and decides whether blood tests are useful. Depending on your complaints, iron (ferritin) or the thyroid gland can be examined, for example.

A handy order:

1. Note what you see. Since when, how many hairs, everywhere or in fixed places such as the crown or the parting.
2. Go to the doctor and tell them which supplements you are already taking, especially if they contain biotin.
3. Have blood inject if the doctor deems it necessary.
4. Only supplement what is deficient, in the dosage recommended by the doctor or pharmacist.

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What if your blood values ​​are good?

Then a nutritional deficiency is probably not the cause, and an extra vitamin usually does not solve the problem. Temporary hair loss after stress, fever or childbirth often recovers on its own. If your hair is gradually thinning at the inlets, on the crown or along the parting, this is often hereditary hair loss. There, minoxidil is the best-researched option that you can buy without a prescription. You can read what you can realistically expect from this in does minoxidil work?

Minoxidil only works as long as you use it and not for everyone. Do not use it if you are pregnant or breastfeeding, if you are under 18, or if you have heart or blood pressure problems without first consulting your doctor. Always read the package leaflet. Women generally use 2% lotion 2 times a day or 5% foam 1 time a day.

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Frequently asked questions

Which vitamin helps against hair loss?

No vitamin is guaranteed to help. Supplementation is only useful if you have a deficiency, for example of iron or vitamin D. Without a deficiency, there is little evidence that extra vitamins make your hair grow^[1].

Can a vitamin B12 deficiency cause hair loss?

That has not been well demonstrated. The overview study found too little data to recommend vitamin B12 or folic acid for your hair^[1]. If you have complaints such as fatigue or tingling, have this examined by your doctor.

How long does it take for your hair to recover after replenishing a shortage?

Hair grows slowly, so count on a few months before you see a difference. The exact duration varies per person and per cause. Follow your doctor's advice about how long to supplement and when to have it tested again.

Can you use minoxidil and vitamins at the same time?

Yes, you can. A supplement supplements any deficiency, minoxidil focuses on hereditary hair loss. Always report biotin for a blood test. In case of bald spots, thyroid complaints or hair loss during menopause, the doctor comes first.^[4].

Should I always go to the doctor if I have hair loss?

In any case, go if you suddenly lose a lot of hair, get bald spots or are worried about it^[2]. In case of bald spots, thyroid complaints or hair loss during menopause, the doctor comes first.

This article is general information and does not replace medical advice. Always read the package leaflet and, if in doubt, consult your doctor or pharmacist. Prices are as of November 2026.

Sources

1. Almohanna HM, Ahmed AA, Tsatalis JP, Tosti A. The Role of Vitamins and Minerals in Hair Loss: A Review. Dermatology and Therapy, 2019 (English).
2. Thuisarts.nl (NHG). I have hair loss. What could it be?
3. Nutrition Center. Vitamin D: advice for a supplement (2026).
4. U.S. Food and Drug Administration. Biotin Interference with Troponin Lab Tests (English).