Thinning Hair and Your Thyroid: Why the Biotin in Your Hair Vitamins Can Skew the Test

When hair starts thinning, two things often happen around the same time: you start a hair vitamin, and your clinician orders thyroid tests. Those two can collide. Here is how thyroid problems affect hair and what to tell the lab before your blood draw.

The thyroid link

Hypothyroidism, an underactive thyroid, affects nearly 5 in 100 Americans. It’s much more common in women and in people over 60.¹ Common symptoms include:¹

• tiredness and weight gain
• feeling cold
• joint and muscle aches
• dry skin and dry, thinning hair

It develops slowly, so symptoms can creep in over months or years.¹ Many of these symptoms are common for other reasons too, so they don’t necessarily mean a thyroid problem.¹

You’re more likely to have it with a family history of thyroid disease or conditions such as celiac disease or diabetes.¹ Large amounts of iodine from kelp, other seaweed or iodine supplements can cause or worsen it in some people.¹

The biotin problem

Biotin is a B vitamin heavily marketed for hair and nails, but there’s little scientific evidence for those claims.² Most people get enough from food, and true deficiency is very rare in the U.S.² Adults need about 30 micrograms a day,² while many hair supplements contain far more.

Supplements with biotin above recommended amounts may cause false results on some lab tests, including tests of thyroid hormone.² A falsely abnormal result could lead to the wrong diagnosis or the wrong dose of thyroid medicine.

Before your blood test

• Tell your clinician and the lab about every supplement you take, including multivitamins and hair, skin and nail blends.²
• Ask whether to pause biotin before the test, and for how long.
• Check labels. Biotin may be listed as vitamin B7 or vitamin H.

Our guides to hair vitamins and biotin, why hair thins, iron and hair loss and taking thyroid medicine explain more.

Questions to ask

1. Could my thyroid explain my hair changes?
2. Should I stop my biotin before the test?
3. If my thyroid is treated, how long before my hair improves?
4. What else should we check?

Try: “My hair has been thinning and I feel tired and cold. Could we check my thyroid? I take a hair supplement with biotin. Should I stop it before the blood test?”

Hair, Everywhere includes a Hair Check and a monthly Hair Log. Use them to list supplements and test dates along with changes in your hair. See the book.