Vitamins for hair loss: biotin, iron, zinc and vitamin D

Can biotin, iron, zinc or vitamin D help with hair loss? The answer depends on which of two questions is being asked. This page separates the two, goes through what was studied for each nutrient, and then says where that leaves a man whose hair is thinning at the hairline or the crown.

Deficiency or regrowth: two different questions

A vitamin or mineral can matter for hair in two ways. The first is a documented deficiency: a clinician has found that the body is short of a nutrient, and correcting it has its own medical reasons. The second is taking a supplement in the hope of more hair when no deficiency has been found. Studies of the first do not answer the second. ^{[1, 2, 3, 4, 5]}

A systematic review published in JAMA Dermatology in 2022 gathered the trials of nutritional supplements for hair loss in people with no known deficiency, with a search that ran to October 2021. We read its summary and use it as a map of what has been tested, not as proof for any one ingredient. Our own review of this area was targeted, not exhaustive, and several of the studies below could be read only as published summaries. Where that is the case, we say so. ^[6]

This also matters for the kind of hair loss. Much of the research below is about diffuse shedding, not about the gradual thinning of male pattern hair loss. If you are not sure which one you have, the page on types of hair loss comes before this one.

The four nutrients at a glance

We found no trial in men with pattern hair loss that shows regrowth with any of the four. What each one does have is summarised here, with the detail in the sections that follow.

In the ingredient library all four carry the same label, "Not for your context". It means there is no basis to add them by default, and that they may become relevant with a documented deficiency. It does not mean they have been shown to do nothing.

Does biotin help with hair loss

For a closer look at this ingredient, read biotin for hair growth, including the studies in people without a known deficiency and the laboratory-test issue.

Where biotin clearly matters

Hair loss linked to a diagnosed biotin deficiency has been described as improving once the deficiency was corrected. The NIH fact sheet describes that deficiency as rare, and the evidence for biotin supplements in hair and nails as limited. Those cases say nothing about people whose biotin is adequate. ^{[1, 7]}

The trials in people with no known deficiency

The oldest trial dates from 1966. Forty-six women with diffuse hair loss took 10 mg of biotin a day or a placebo for four weeks, and no significant difference between the groups was reported. We know this trial only through a 2024 review, not from the original paper, and four weeks is short. ^[7]

In 2024 a small study gave 10 healthy men 5 mg of biotin a day for 14 days. The men did not have hair loss. The researchers measured how fast hair grew on a patch of one square centimetre at the back of the head, and the speed did not change. No funding or conflict of interest was declared. ^[8]

The same study had a period with 5% minoxidil on the scalp and a period with both together. Growth speed rose in the combined period, from 2.36 to 2.64 mm a week, and that before-and-after change was significant for the combination and not for either product alone. We found no verified comparison in the study showing that biotin adds anything to minoxidil, and it had no placebo. We do not read it as evidence that the two work better together. ^[8]

A 2025 trial tested a plant extract supplying 1.25 mg of biotin, with or without silica, against placebo in 105 adults for 90 days. Its summary reports improvements in the groups taking the extract but gives no clear comparison with placebo, and we could not confirm what kind of hair loss the participants had or whether they were short of biotin. Authors of the paper declared employment with two companies. It is not a trial of biotin on its own. ^[9]

Biotin and laboratory tests

Two practical details go with this. No upper limit has been set for biotin, which is not a statement that any amount is safe. ^[1] And labels give amounts in milligrams (mg) on some products and micrograms (µg) on others: 5 mg is the same as 5,000 µg. The same nutrient can also be in a multivitamin and a hair formula at once.

Iron and ferritin: what a low reading does and does not show

The iron studies we reviewed are about women. A pooled analysis of 36 studies and 10,029 participants, most of them observational, found lower ferritin in women with hair loss that does not scar the scalp. Ferritin is a blood marker used to judge iron status. An association of this kind does not show that raising a ferritin level that is already adequate regrows hair. We read this analysis in its published summary. ^[10]

A 2024 study followed 200 women aged 18 to 65 with telogen effluvium, a diffuse shedding of hair, who took iron. The group is described by its authors as not low in ferritin, although the summary also includes women with lower or unknown levels. It recorded how satisfied they were, not how much hair they had, and it had no untreated group to compare with. Satisfaction was associated with a starting ferritin reading of 50 or above. Its authors declared no conflicts of interest. ^[11]

Our research does not derive a ferritin target of 50 or 70 for hair. No study we reviewed shows that reaching such a figure makes hair regrow. ^{[10, 11, 5]}

Zinc: what was studied

We reviewed two zinc studies, and neither is about men with pattern hair loss. The first is a report of five people with telogen effluvium and a documented zinc deficiency who were given zinc by mouth. All five improved or recovered, according to the authors. There was no comparison group, and the summary we read does not give the amount. ^[12]

The second is a trial of 73 women aged 15 to 45 with hair loss, split into four groups for four months: zinc sulphate, calcium pantothenate, both together, or 2% minoxidil solution. There was no placebo. Hair density improved most with minoxidil, and zinc was not shown to be better. The summary does not say whether the women were short of zinc, what kind of hair loss they had or how much zinc the tablets supplied. Its authors declared no conflicts of interest. ^[13]

So zinc has a place when a deficiency has been documented, and no established place as a routine supplement for pattern hair loss. The evidence is limited, which is different from evidence that it does nothing.

Vitamin D and hair loss: what the studies compared

Low vitamin D has been associated with hair loss. Being found together does not show that one causes the other. The three studies we reviewed were all done in women, and none of them settles the question. ^{[14, 15, 16]}

The comparison in women with pattern hair loss was read only as a summary, like the 2021 study. It suggests that vitamin D added to minoxidil did better than minoxidil alone, in women whose vitamin D was lower than that of a comparison group at the start. It does not say what vitamin D does for a man with pattern hair loss, or for anyone whose level is adequate. ^[16]

Other nutrients, protein, collagen and omega oils

More nutrients does not mean more hair. For two of them, too much is itself a recognised cause of hair loss. ^{[5, 17, 18]}

Hair formulas: the result belongs to the whole product

Many hair supplements are not one nutrient but a mixture: vitamins, minerals, amino acids and plant extracts in one capsule, sometimes studied together with a shampoo. Some of these products have been tested against placebo, and some of the results are positive.

The rule for reading them is simple. The trial tested the whole product, so the result belongs to the whole product. It is not evidence for any single ingredient in it, and it does not carry over to another product with a similar list. The same rule applies to the botanicals we profile: see what the saw palmetto profile says about blends and the note on oil blends that contain rosemary.

Four formulas tested in groups that included men

The fenugreek column shows why the measure matters. The share of hairs in the growing phase rose by 5.9 percentage points with the formula and by 0.62 with placebo. Hair density changed by 6.5 hairs per cm² with the formula and by −7.1 with placebo, a difference that was not statistically significant. A result on one measure is not a result on another. ^[29]

The first column shows how easily a formula result is misread. The product was a package: one capsule twice a day, plus a shampoo, a conditioner and a serum every day. Nothing in the trial says what the capsule did alone. The capsule lists more than twenty ingredients, among them biotin, zinc, vitamin D, selenium and vitamin A, without the amount of each. ^{[25, 26]}

Two more details belong next to that chart. When all hairs were counted in the men, not only the thicker ones, the difference from placebo was not significant. And no side effects were reported, in groups too small to rule out rare ones. ^{[25, 26]}

A formula added to medicines

One trial tested a formula on top of treatment. In 13 centres in Italy, 225 people with pattern hair loss (165 men and 60 women) either added a daily capsule of saw palmetto, pumpkin seed, cystine, vitamin C and zinc to the hair-loss medicine chosen for them, or took the medicine alone. The people who rated the photographs after six months did not know who was in which group. ^[31]

The medicines differed from person to person: about half used minoxidil, around one in twenty took finasteride tablets, and most of the others used pharmacy-made preparations. The amounts of vitamin C and zinc in the capsule were not given. The result says something about that capsule in that setting. It does not show what zinc, saw palmetto or pumpkin seed oil adds to a medicine. ^[31] The page on hair loss routines covers what has been tested as an addition to a medicine.

Formulas tested only in women, and pooled reviews

Other formulas we looked at were tested only in women who described their own hair as thinning, without a single diagnosis: 60 women for 90 days in one trial, 40 women for six months in another, both with company funding. Their results favoured the formulas. They do not carry over to men with pattern hair loss. ^{[32, 33]}

Two recent reviews pooled trials like these: 14 studies and 967 people in one, 19 studies and 1,658 people in the other. They combine different diagnoses, different formulas and different measures, and we have not audited them in full, so we take no ranking and no average effect from them. ^{[34, 35]}

What too much can do: cautions in the official fact sheets

Supplements sold for hair are easy to stack: a multivitamin, a hair formula and a single nutrient can all contain the same thing. The official fact sheets we used describe what happens at the other end, when intake is too high. ^{[1, 2, 3, 4, 17, 18, 36, 5]}

Where this leaves a man with pattern hair loss

If your hair is thinning gradually at the hairline or the crown and no deficiency has been found, the studies above give no reliable reason to expect regrowth from biotin, iron, zinc or vitamin D. Most were done in women, in people with a different kind of hair loss, or in healthy volunteers. That is why the four sit outside our ranking, under a label of their own.

What does have trial evidence in men is a short list, set out in three tiers. The page minoxidil vs finasteride compares the two that share the top tier.

The two medicines in the top tier were each tested in men against a product with no active ingredient. The UK product information reports a trial of 352 men aged 18 to 49: 5% minoxidil foam added about 21 hairs per square centimetre in the measured area after 16 weeks, against about 4 with the same foam without minoxidil. The US label reports two trials of 1,553 men with thinning at the crown: those taking finasteride 1 mg had 107 more hairs than those on placebo after 12 months, in a measured patch of 5.1 cm². Both bring conditions and side effects of their own, which the minoxidil and finasteride profiles set out, and dutasteride is a prescription alternative with a separate assessment. ^{[37, 38]}

Where to go next

If you came here to find out what is worth trying for pattern hair loss, the next page is the comparison, not another supplement.

For how the pieces fit together, read what to combine and what to choose between, or the shorter section on building a routine without adding everything. If you would like to be pointed to the relevant part, take the short hair questionnaire. It does not diagnose hair loss or a deficiency. How we weigh evidence is on the methodology page.