Ferritin, Thyroid, Vitamin D: The Blood Tests for Hair Loss

Somebody eventually tells you to “get your bloods done”. It sounds like a formality — a box to tick before the real conversation about hair. Then the results come back, everything is marked within range, and you are exactly where you started, except now with a printout.

That printout is often where the answer was hiding. Not because a lab flagged something, but because of what nobody explained: for hair, “within range” and “adequate” are two very different things.

The short answer: five tests do most of the work in hair loss investigation — ferritin, a full thyroid panel, vitamin D, vitamin B12 and a complete blood count. Ferritin below roughly 30 ng/mL is widely considered too low for healthy hair even when a lab calls it normal, and thyroid dysfunction can produce diffuse shedding months before any other symptom appears. Correcting a genuine deficiency takes 3 to 6 months before hair responds.

Which deficiencies actually cause hair loss

The internet will hand you a list of twenty nutrients. Clinically, the list is much shorter, and the difference matters because chasing the wrong ones wastes months.

Iron deficiency, thyroid dysfunction and severe protein restriction have the clearest relationships with diffuse shedding. Vitamin D deficiency is strongly associated with several hair disorders, though the causal picture is less settled than supplement marketing suggests. Zinc matters when it is genuinely low, which is uncommon in people eating a mixed diet, and B12 matters mainly in vegans, older adults and people on certain long-term medications.

What does not cause hair loss: biotin deficiency in anyone who eats normally, “detox” issues, or a slightly low reading on a nutrient your body has plenty of stored. Biotin deserves a specific warning — high-dose supplements can distort several immunoassay tests, including thyroid panels and cardiac markers, which is why laboratories increasingly ask you to stop it for several days before a blood draw.

Ferritin: the number that matters most

Ferritin measures stored iron rather than circulating iron, which makes it the most useful single hair test. You can have completely normal haemoglobin, no anaemia at all, and still have empty iron stores — and the hair follicle notices long before your red blood cells do.

Most laboratories report a normal range starting somewhere between 10 and 15 ng/mL, because that range is designed to catch anaemia rather than to support hair growth. Dermatology literature commonly uses a functional threshold nearer 30 ng/mL, and some clinicians prefer 40 to 70 for patients with active shedding. This is why so many patients are told their iron is “fine” while sitting at 14.

One caution: ferritin also rises with inflammation and infection, so a single high-ish value in someone who is unwell can be misleading. Interpretation belongs to a doctor who can see the full panel, not to a search engine and a screenshot.

Why iron drops without anaemia

Iron stores fall for boring, common reasons. Menstrual blood loss is the largest by far, and heavy periods can drain ferritin steadily for years without ever producing anaemia. Reduced intake is second — vegetarian and vegan diets, or simply eating far less than before.

Rapid weight loss belongs on this list too. Anyone who has dropped a significant amount of weight quickly, including patients on appetite-suppressing medication, is at real risk of both low iron and low protein intake at the same time. We covered that combination in detail in what GLP-1 medications do to your hair.

Gastrointestinal causes matter as well. Coeliac disease, chronic use of acid-reducing medication and gut absorption problems all reduce iron uptake regardless of what you eat, which is why persistent low ferritin should be investigated rather than simply supplemented forever.

Thyroid: the great imitator

Thyroid disease produces diffuse hair thinning that looks exactly like nutritional shedding, and it frequently arrives before the classic symptoms are obvious. Fatigue gets blamed on work, weight change on diet, and hair on genetics.

A useful panel includes TSH plus free T4, and free T3 or thyroid antibodies where clinically indicated. TSH alone is the standard screen but it is not the whole story, and borderline results in a patient with unexplained shedding deserve a second look rather than a shrug.

Both directions cause hair loss. An underactive thyroid produces coarse, dry hair and diffuse thinning; an overactive one produces fine, soft hair that sheds easily. In either case the hair usually recovers once thyroid function is properly treated and stable — but recovery lags treatment by several months, which is a frequent source of unnecessary despair.

Vitamin D: real association, overstated fix

Low vitamin D turns up repeatedly in patients with telogen effluvium, female pattern hair loss and alopecia areata. Vitamin D receptors are present in the hair follicle and appear to be involved in cycling, so the biological plausibility is real.

What is less certain is how much correcting a deficiency improves hair by itself. Supplementation reliably fixes the blood value; the hair response is more variable and often modest. Treat it as removing an obstacle rather than as a treatment.

Dosing is a medical decision, not a shelf decision. Vitamin D is fat-soluble and accumulates, and high-dose regimens without monitoring can cause harm. Ask your doctor for a level, then a dose based on that level, then a recheck.

Zinc, B12 and the rest of the panel

Zinc deficiency causes hair loss, but it is genuinely uncommon in people eating a varied diet in a country without endemic deficiency. It is worth testing in patients with malabsorption, restrictive diets, or after bariatric surgery. Supplementing zinc without a low result is not neutral — excess zinc interferes with copper absorption.

B12 matters most for vegans, people over sixty-five, and anyone on long-term metformin or acid-suppressing medication. Low B12 causes fatigue and neurological symptoms first, with hair change further down the list, but it belongs in the panel because it is cheap to test and easy to correct.

A complete blood count rounds it out, catching anaemia and giving a general picture. In women with signs of excess androgens — irregular cycles, adult acne, unwanted facial hair — a hormonal panel is added, which is a separate conversation we cover in the context of female hair loss assessment.

The tests worth requesting, in one list

• Ferritin — stored iron, the single most useful hair value.
• Full blood count — anaemia and general status.
• TSH and free T4 — thyroid function, with antibodies if indicated.
• Vitamin D (25-OH) — deficiency is common and easily missed.
• Vitamin B12 — especially with plant-based diets or long-term medication.
• Zinc — where diet, absorption or surgery history suggests it.

Your family doctor can order all of these, and in most healthcare systems they are inexpensive and routine. You do not need a specialist to request them, and you should not be paying for an exotic “hair panel” of forty markers of unclear value.

Take the results with you to any consultation about your hair. At Hairpol we ask for them regularly, because a scalp examination interprets very differently depending on what the bloods say.

How to read your results without panicking

Two rules make this manageable. First, look at where you sit inside the range, not just whether you are inside it — a ferritin of 12 and a ferritin of 90 are both “normal” and mean entirely different things for hair.

Second, do not treat a single out-of-range value as a diagnosis. Values move with hydration, illness, recent meals and the time of day. A doctor looking at the whole panel plus your history will reach a very different conclusion than you will reading one line in isolation.

If you are shedding heavily and every value truly is comfortable, that is useful information too. It redirects the investigation toward causes that bloodwork cannot see — pattern hair loss, scalp inflammation, or a trigger that has already passed and is still working its way through the cycle.

How long correction takes before hair responds

This is where most people give up too early. Repleting iron stores takes about 3 to 6 months of consistent supplementation, and the follicle then needs its own cycle time on top of that before new growth is visible.

Realistically, expect the shedding rate to settle first, usually within two to three months of correcting the deficiency. Visible regrowth of short new hairs comes later, around months four to six, and appreciable density change is a nine to twelve month proposition.

Nothing about that timeline can be shortened by taking more of something. Doubling an iron dose will not double the speed; it will mostly produce gastrointestinal side effects and, in the wrong patient, iron overload. This is why iron should only be taken with a documented low level and medical supervision.

When your bloodwork is normal and you’re still shedding

Clean bloods do not mean nothing is wrong. They mean the answer is somewhere else, and there are three common places to look.

The first is a trigger that has already passed. Illness, surgery, a crash diet, childbirth, high fever or severe stress can each set off a shed that appears two to four months later, by which point the cause has resolved and shows on no test. Our explainer on why sudden shedding is not balding covers this pattern in full.

The second is androgenetic hair loss, which does not show up in blood at all. The third is a scalp condition — inflammation, seborrhoeic dermatitis, or a scarring process — which requires the scalp to be examined rather than the blood to be re-tested. If shedding continues without explanation, the next step is a proper scalp assessment, and you can book a photo assessment to get a view before travelling anywhere.

Do these tests matter before a hair transplant?

Yes, for two separate reasons, and they are worth separating.

The surgical reason is straightforward: healing and graft survival happen in a body, and a patient who is iron-depleted or has untreated thyroid disease is not in optimal condition for a long procedure. Standard pre-operative bloods cover safety, and we look at the hair-specific values alongside them.

The planning reason matters more. If a portion of your loss is nutritional or thyroid-driven, that portion will improve without surgery — and operating before it resolves means transplanting into a scalp that is about to change. That is how patients end up with density that looks unbalanced a year later. The same principle applies to anyone with diffuse thinning asking about candidacy.

Testing in women versus men

Women get more from bloodwork than men do, statistically speaking. Low ferritin is far more common, thyroid disease is more common, and diffuse female pattern loss overlaps clinically with both — so the tests genuinely change management.

In men, a young patient with a receding temple and an intact crown usually has androgenetic hair loss, and no blood test will confirm or refute it. Testing still has value when the loss is diffuse, sudden, or accompanied by other symptoms, but it should not delay a conversation about the pattern itself, described in how DHT drives hair loss.

Adolescents and patients with rapid, unusual or patchy loss are a different category again and should be examined rather than tested by list. Patchy round bald areas in particular are not a nutritional problem and need a dermatological opinion.

The tests people request that rarely help

Two requests come up constantly in consultations, and both usually waste money.

The first is a total testosterone level in a man with a receding hairline. Androgenetic hair loss is about follicle sensitivity to DHT, not about how much testosterone circulates in your blood, and men with entirely normal levels lose hair while men with high levels keep it. A hormone panel earns its place when there are other signs — very early onset, loss of libido, gynaecomastia — not as a routine add-on.

The second is hair mineral analysis, sold as a test of your “nutrient status” from a snipped sample. It is not a validated way to assess body stores, results vary between laboratories for the same sample, and the recommendations that follow are usually a supplement order form. Spend the same money on ferritin and a thyroid panel instead.

Food intolerance panels and heavy metal screens belong in the same category unless there is a specific clinical reason. If a clinic proposes a long list of unusual tests before anyone has examined your scalp, that sequence is itself the warning sign.

Supplements: what to take and what to skip

Supplement only what your results show is low, and do it under medical guidance. Iron in particular should never be taken blind; iron overload is a real condition and it is not reversed by stopping the tablets quickly.

The multi-ingredient “hair, skin and nails” products are the least efficient way to correct a specific deficiency. They typically contain a large dose of biotin, which does nothing for you if you are not deficient and can interfere with blood tests, plus small doses of everything else.

Protein is the item most often ignored and most often relevant, especially in patients eating far less than they used to. It is not a supplement question; it is a food question, and it is covered from the recovery angle in how diet and nutrition affect results.

Where clinic treatment fits once the bloods are corrected

Once deficiencies are addressed and stable, non-surgical treatment becomes worth discussing. PRP and mesotherapy under our hair treatments are far more likely to produce a visible response in a scalp that is no longer nutritionally starved.

Sequencing matters here. Running a course of in-clinic treatment while ferritin sits at 12 and thyroid is untreated will mostly generate an expensive disappointment, and the treatment gets blamed for a problem it was never designed to solve.

Medication for pattern loss follows the same logic and always requires a prescriber’s assessment. Minoxidil and finasteride address hormonal miniaturisation; they do not correct iron, and starting them during an active deficiency-driven shed makes it impossible to tell what is working.

What to do with the results sitting in your inbox

Open them and find four lines: ferritin, TSH, vitamin D and haemoglobin. Note the exact numbers rather than the flags. If ferritin is under 30, thyroid values sit at either edge of the range, or vitamin D is low, you have something concrete to discuss with a doctor rather than a vague worry to carry around.

Then give it time. A correction started this month shows in your hair somewhere between month four and month nine, and the only way to see it is standardised photographs taken monthly in the same light.

If your numbers are clean and the shedding continues, that is the point to have the scalp itself looked at. You can send photographs through our contact page, and our frequently asked questions cover what happens next. Whatever the answer is, it is better than another year of guessing about a printout nobody explained to you.