Hair Fall from Thyroid, Iron or Vitamin Deficiency: Tests to Know

Thyroid disorders and low levels of iron, and less clearly vitamin D, vitamin B12 or zinc, can cause or worsen diffuse hair shedding, where hair thins all over the scalp rather than in patches. A dermatologist will usually examine your scalp and ask about your health first, then may order blood tests such as a blood count, ferritin, thyroid function and selected vitamin levels, because treating a proven deficiency or thyroid problem can help while random supplements often do not.

Hair fall is one of the most common reasons people in India see a dermatologist, and many arrive having already tried several oils, shampoos and hair vitamins. This guide explains how thyroid problems and nutrient deficiencies affect hair, which tests may be useful, and why testing before supplementing matters.

How do thyroid problems and deficiencies cause hair fall?

Each hair follicle cycles between a growing phase and a resting phase. When the body is under stress from illness, hormonal change or a lack of nutrients, more hairs can shift into the resting phase at the same time and then fall out together a few weeks to months later. DermNet calls this telogen effluvium, and lists thyroid disease and iron deficiency among its possible causes.

This kind of hair fall is usually diffuse. You may notice more hair on the pillow, in the shower drain or on your comb, and a thinner ponytail, rather than bald patches.

Can thyroid problems cause hair loss?

Yes. The American Academy of Dermatology (AAD) says a thyroid problem can cause thinning hair and that some people notice hair coming out in clumps when brushing. Importantly, the AAD also says treating the thyroid disease can reverse the hair loss.

The NHS lists other symptoms of an underactive thyroid (hypothyroidism) that can help you and your doctor connect the dots:

• Tiredness and feeling cold
• Weight gain
• Constipation
• Dry skin, dry hair or hair loss
• Low mood
• Irregular or heavy periods

An overactive thyroid can also cause hair thinning, along with weight loss, a fast heartbeat, sweating and anxiety. Thyroid conditions are common in Indian women, so thyroid testing is often part of a hair fall work up when symptoms suggest it.

Can low iron cause hair fall?

Iron deficiency is one of the most discussed causes of hair shedding, especially in women with heavy periods, during and after pregnancy, and in people on vegetarian diets low in iron. The NHS lists hair loss among the symptoms of iron deficiency anaemia, alongside tiredness, shortness of breath, pale skin and headaches.

A review in Dermatology Practical and Conceptual explains the evidence is mixed:

• Some studies found low ferritin (iron stores) more often in women with chronic shedding and pattern hair loss, while others did not
• A normal ferritin does not fully exclude iron deficiency, because ferritin rises with inflammation
• Experts who see many patients with hair loss test iron levels and treat iron deficiency, with or without anaemia, under monitoring
• Taking iron without monitoring carries a risk of iron overload and toxicity

This is why you should not start iron tablets on your own just for hair fall.

What about vitamin D, B12, zinc and biotin?

The same review summarises what is known:

Nutrient	What the evidence suggests
Vitamin D	Low levels have been reported in some people with shedding and pattern hair loss, but cause and effect is not proven
Zinc	Deficiency can cause shedding and brittle hair. Screening is suggested for people with risk factors. Excess zinc can be harmful
Vitamin B12 and folate	Deficiency causes anaemia and tiredness and may be checked, especially in vegetarians
Biotin	Deficiency is rare. No clinical trials show benefit for hair loss without a deficiency
Selenium, vitamin A, vitamin E	Too much has been linked to hair loss

The review’s key message is that deficiencies should be corrected, but people without a deficiency should be told that there is little research supporting supplements and that some carry a risk of worsening hair loss or toxicity. For more, see our article on collagen and biotin supplements.

Which tests might a dermatologist order for hair fall?

The AAD explains that dermatologists examine the scalp, hair and nails, may gently pull on the hair, and may order a blood test or scalp biopsy if they suspect a disease, vitamin deficiency, hormone imbalance or infection. The review on nutrition advises testing based on history and risk factors rather than ordering every test for everyone.

Tests your dermatologist may consider include:

• Complete blood count (CBC) to look for anaemia
• Serum ferritin and iron studies to assess iron stores
• Thyroid function tests, usually TSH and sometimes thyroid hormone levels
• Vitamin D level
• Vitamin B12 and sometimes folate
• Zinc, if there are risk factors such as poor diet or gut problems
• Hormone tests if you have irregular periods, acne or excess facial hair that suggest PCOS. See our PCOS skin and hair guide
• Other tests based on your symptoms, such as blood sugar

Your dermatologist will interpret the results together with your scalp examination, because a mildly abnormal value does not always explain the hair fall.

How long does it take for hair to recover?

Hair grows slowly, so patience is part of treatment. DermNet explains that in telogen effluvium, increased hair fall is usually noticed 2 to 4 months after the triggering event, peaks, and then gradually returns to normal over 6 to 9 months in most people. Recovery may be incomplete in some cases, and in some people shedding continues for longer periods.

In practice this means:

• Shedding may continue for a while even after a thyroid problem or deficiency has been corrected
• New short hairs along the hairline and parting are often the first sign of regrowth
• Telogen effluvium does not cause complete baldness, as DermNet notes, although it can reveal underlying pattern hair loss

Could my hair fall have another cause?

Thyroid problems and deficiencies are only some of the causes. Others include:

• Hair fall after fever, dengue, typhoid or COVID. See our guide on hair loss after fever
• After childbirth. See postpartum hair loss
• Pattern hair loss in women and men, where a widening parting or receding hairline develops gradually. Read hair fall in women and male pattern baldness
• Alopecia areata, with round bald patches
• Crash dieting, major stress, surgery and some medicines
• Scalp conditions such as dandruff or fungal infection
• Tight hairstyles and harsh treatments such as rebonding and bleaching

Often more than one cause is present at the same time.

What can I do while I wait for tests?

• Eat regular, balanced meals with enough protein, such as dal, pulses, paneer, eggs, fish or meat, along with leafy greens and fruit
• Avoid crash diets
• Be gentle with your hair. Avoid tight buns and ponytails, frequent heat styling and harsh chemical treatments
• Do not start iron, zinc, vitamin D or high dose hair vitamin tablets without testing
• Keep a record of when the hair fall started and any illness, stress, new medicine or diet change in the months before

You may also find this guide useful: Nail Problems: What White Spots, Ridges and Colour Changes Mean.

When to see a dermatologist

See a dermatologist if:

• Hair shedding continues for more than a few months
• You notice bald patches, a widening parting or a receding hairline
• You also have tiredness, weight change, feeling cold, heavy periods or palpitations
• You have irregular periods, acne or excess facial hair
• Your scalp is itchy, scaly, red or painful
• You have been taking supplements for months without improvement

Dr. Maria offers online consultations where she can review your history, look at photos of your scalp and suggest which tests, if any, are worth doing.