Biotin for Hair and Nails: What the Research Actually Says

Biotin (vitamin B7) is a water-soluble B vitamin involved in fatty acid synthesis and amino acid metabolism — both relevant to keratin, the structural protein that makes up hair and nails. That much is well established.

Where the evidence is strong

True biotin deficiency, while rare, is well documented to cause hair thinning and brittle nails. In deficient individuals, correcting the deficiency reliably improves these symptoms. This is the strongest evidence base behind biotin supplementation.

Where it's thinner

For people who are not biotin-deficient, the evidence that additional biotin meaningfully improves hair or nail strength is less robust than typical marketing implies. Most biotin supplements, including gummies like Gellaagen, provide well above the standard daily value — a normal approach for this category, and not a safety concern since excess biotin is water-soluble and simply excreted.

One thing worth knowing

High-dose biotin is documented to interfere with certain lab tests, particularly thyroid and cardiac panels, in ways that can produce inaccurate results. If you're having bloodwork done, mention any biotin supplement to your clinic beforehand.

The bottom line

Biotin has a real, established role in keratin production. Whether supplementing above your dietary baseline produces a visible change depends heavily on whether you had a gap to begin with.