Is your hair and nail supplement messing with your thyroid tests!?

Your thyroid plays a crucial role in metabolism, growth and development.

Treating hypothyroidism is pretty simple and safe (29): generally we replace the missing thyroxine (T4) with levothyroxine, a synthetic form. Treating hyperthyroidism on the other hand carries some serious risks. The antithyroid medications propylthiouracil and methimazole carry risks of skin rash, allergic reactions, agranulocytosis (severely low levels of white blood cells including neutrophils) and hepatotoxicity (liver injury).

Unfortunately there is a common over the counter supplement that can lead to false diagnosis of hyperthyroidism: Biotin.

What is biotin and how can it affect thyroid function tests?

Biotin is a common over the counter supplement touted for beneficial effects on hair and nail health. Doses of biotin between 5 and 10mg (5000 to 10,000 mcg) per day can falsely raise T3 and T4 while falsely lowering TSH (30). This can lead to false diagnosis of hyperthyroidism and inappropriate prescribing of risky medications for it’s management (31).

Oh no! I’m taking a supplement with biotin in it! What do I do?

Take a breath. There’s no need to throw out your expensive prenatals. While that is an option, you can also let the biotin wash out of your system before going for thyroid blood work. How long should you stop taking them for? For doses of biotin up to 10mg (10,000 mcg) per day it is suggested that you hold them for 48 hours (30). For doses above that, a longer washout may be needed. As per usual, ensure that you inform your healthcare team of all medications, vitamins and supplements that you use. If you’ve been diagnosed with hyperthyroidism or Graves disease and you were taking biotin during that diagnosis it is important to reassess that diagnosis.

Thanks for reading and be well!

xo Kimberley