Iron, vitamin D, B12, thyroid: which blood tests matter for hair fall?

Key takeaways

• Ferritin, not just haemoglobin, is the iron test that matters for hair. You can have low iron stores without being anaemic.
• A 2022 meta-analysis found women with non-scarring hair loss had significantly lower ferritin than women without it.
• Thyroid problems, both overactive and underactive, can trigger shedding, and they are easy to check.
• Hormone tests are useful mainly for women with irregular periods, acne or excess facial hair.
• Stop biotin supplements before blood tests and tell your doctor about them. Biotin can distort some results, including thyroid tests.

Do I really need blood tests for hair fall?

People often come in holding a long test package report and say, "Doctor, everything is done, now tell me why my hair is falling." I'm happy to read it. But honestly, not everyone needs all of that. A review in Dermatology Practical and Conceptual recommends that doctors first assess risk through your history, diet and examination, and order tests only when warranted. If a man in his twenties has a receding hairline exactly like his father's, eats well and is otherwise healthy, a big panel of tests rarely changes my plan.

Where I do find tests useful: - Shedding is sudden and diffuse (all over the scalp). - Hair loss follows an illness, pregnancy, surgery or weight loss. - You have heavy periods, a vegetarian or restricted diet, or symptoms like tiredness, weight change or feeling cold. - Thinning is not improving with treatment the way I expected.

Which tests matter, and why?

DermNet advises correcting thyroid, iron, B12 and folate abnormalities when managing shedding, and recommends thyroid and sex hormone tests in female pattern hair loss when the history suggests it. That matches how I work: the history decides the tests, not the other way round.

Why is ferritin so important?

See, what happens is, haemoglobin tells you whether you are anaemic. Ferritin tells you how much iron you have kept in reserve. Hair follicles are among the busiest cells in the body, and when stores run low, the body appears to look after the essential organs first. Hair is not on that list.

A 2022 systematic review and meta-analysis in Skin Appendage Disorders, covering 36 studies and over 10,000 women, found: - Women with non-scarring hair loss had significantly lower ferritin than healthy women. - Around 59% of women with hair loss had ferritin below 30 to 40 ng/mL. - Iron deficiency anaemia itself was not more common in women with hair loss.

That last point is very important to understand. A "normal" haemoglobin does not rule out low iron stores. Now, the study shows an association. It does not prove that taking iron will regrow hair in everyone. But in India, where the National Family Health Survey (NFHS-5) found 57% of women of reproductive age to be anaemic, checking ferritin is practical and inexpensive. So I usually do it.

One more thing. Iron should be taken only after testing and under medical advice. More iron is not automatically better, and too much is not harmless.

Does vitamin D deficiency cause hair loss?

Low vitamin D is very common in India, despite all our sunshine, especially if you spend the whole day indoors in an office. Research has looked at links between low vitamin D and several hair conditions, and some studies of post-COVID shedding found it alongside other deficiencies. But the evidence that vitamin D supplements regrow hair in people with pattern hair loss is weak.

So my practical view is simple. If your vitamin D is low, correct it, because it matters for your bones, muscles and general health. Just do not expect it alone to fix pattern thinning.

What about B12 and thyroid?

Vitamin B12 comes mainly from animal foods: dairy, eggs, fish and meat. Strict vegetarians who take little milk or curd, and people on long-term acid-reducing or diabetes medicines, are more likely to be low. DermNet lists B12 among the deficiencies to correct in telogen effluvium.

Thyroid disorders are a recognised trigger for diffuse shedding. Both an underactive and an overactive thyroid can do it. I specially mention thyroid problems after delivery for new mothers whose shedding does not settle. See hair fall after pregnancy.

Why can biotin make your reports wrong?

Many hair supplements contain high doses of biotin. The US FDA has warned that high-dose biotin can interfere with many laboratory tests that use a biotin-based method, giving falsely high or falsely low results. Thyroid tests (TSH) and cardiac troponin are among those affected. So you may be taking a "hair vitamin" that quietly confuses the very test we are using to understand your hair.

Before blood tests: - Tell your doctor about every supplement, including "hair, skin and nails" products. - Ask whether to pause biotin before the test.

What if all my tests are normal?

That is common, and it is not a waste. Normal reports are useful information. They point me towards male or female pattern hair loss, chronic shedding without a deficiency, or a scalp condition. The next step is a proper scalp examination, not more blood tests. Read female pattern hair loss or will my hair grow back.

How we approach this at Dr Tvacha

At a Rs 499 hair diagnosis at our Thane, Andheri, Bandra or Dahisar centre, my team and I look at your scalp and history first, then order only the tests that could change your treatment. If you already have recent reports, bring them along so we do not repeat anything. If we find a deficiency, we correct it alongside any hair treatment, and you get the plan and fees in writing. What you do next is your call. See our hair page.

Written by

Dr Amit KarkhanisAesthetic Physician · MBBS, Dip. Dermatology (UK) · Reg. No. 2001/02/1124

Founder of Dr Tvacha, practising in Thane since 2005. Leads the weight loss and hair programmes.