Hair supplements: what has evidence

The one rule: test, don't guess

Hair follicles are among the busiest cells in the body, so a real shortage of iron, protein or certain vitamins can show up as shedding. That is the grain of truth behind hair supplements.

The problem is the jump from "deficiency causes hair loss" to "supplements fix hair loss". If your levels are normal, adding more usually does nothing for your hair, and some nutrients cause harm in excess. Pattern hair loss, the most common kind, is driven by genes and hormones, not by a lack of vitamins.

So before you buy, ask a doctor whether a blood test makes sense. Read when to see a doctor for which tests come up most often.

Biotin

Biotin (vitamin B7) is in almost every "hair, skin and nails" product. A 2017 review looked for all the evidence on biotin and hair.¹ It found 18 reported cases where biotin helped hair or nails, and every one involved an underlying cause, such as a biotin deficiency or a rare genetic condition. The authors found no good evidence that biotin helps healthy people. Real biotin deficiency is rare.

There is also a practical risk. High doses of biotin can interfere with some laboratory tests and give false results, including hormone tests and a test used to diagnose heart attacks.² If you take biotin, tell your doctor and the lab before any blood test.

Verdict: skip it unless a doctor finds a deficiency.

Iron

Iron deficiency is the most common nutritional deficiency in the world, and it is especially common in women who have periods.³ It is one of the classic triggers of shedding.^6,7

What is less clear is whether low iron stores without anaemia cause hair loss, and whether iron tablets help in that case. A detailed review concluded that there is not enough evidence to recommend iron for people with hair loss who are low in iron but not anaemic, and that the decision is a clinical one. Iron-deficiency anaemia, on the other hand, should be treated.³

Too much iron is harmful, especially for people with a common inherited condition called haemochromatosis.³ That is why a ferritin test comes first.

Verdict: test ferritin and a blood count. Take iron if your doctor says you need it.

Vitamin D

Many studies have found lower vitamin D levels in people with several kinds of hair loss. But a link is not proof that one causes the other, and a 2021 review found no conclusive evidence that taking vitamin D corrects hair loss.⁸

Vitamin D matters for your bones and general health, and many people in northern and central Europe run low in winter. If your level is low, correcting it is sensible for those reasons. Just do not expect it to change your hair.

Verdict: worth correcting if low, but not a hair treatment.

Saw palmetto

Saw palmetto is a plant extract that may weakly block the enzyme that makes DHT, the same enzyme that finasteride blocks. A 2020 systematic review found five small randomised trials and two other studies of supplements containing saw palmetto, taken by mouth or put on the scalp.⁴ Results suggested modest improvements in hair count and quality, and it was well tolerated. The authors were clear that robust, high-quality data are lacking, and many of the products mixed saw palmetto with other ingredients, so it is hard to know what did what.

Verdict: a weak, plausible option. It is not a substitute for finasteride, which has far stronger evidence.

Pumpkin seed oil

In a 24-week trial of 76 men with pattern hair loss, those taking pumpkin seed oil capsules had a 40% rise in hair count, against 10% with placebo.⁵ That sounds impressive, but the capsules were a branded mix rather than pure pumpkin seed oil, the company that made them funded the study, and no one has repeated it in a larger trial.

Verdict: interesting, unconfirmed.

Multivitamins and "hair gummies"

Most hair supplements combine biotin, zinc, selenium, vitamins and plant extracts in one product. Mixtures like these are hard to judge: when a trial reports a benefit, it cannot tell you which ingredient helped, or whether the people in it were low in something to begin with. The 2017 European guideline on pattern hair loss made no recommendation for nutritional supplements.⁹

Watch the doses. Products often contain far more biotin than you need, and some combinations add up when you take more than one product.

What to do instead

1. If you are shedding, look for a trigger in the past few months and ask a doctor about a blood count, ferritin and thyroid tests.^7,3 See shedding after stress, illness or birth.
2. If you have pattern hair loss, the treatments with real evidence are minoxidil and, for men, finasteride.
3. Eat enough protein and a varied diet. Crash diets are a known trigger of shedding.⁶
4. If you want to try a supplement anyway, pick one with a single ingredient at a normal dose, tell your doctor, and judge it honestly with progress photos after six months.