Running short of biotin is uncommon, and usually has a reason
Biotin is in eggs, nuts and legumes, and gut bacteria make more. Where people do run short there is usually a cause: long-term antibiotics, anticonvulsants, or intravenous feeding.
What the study found
Biotin deficiency is rare, and has a short list of real causes
Biotin is in eggs, nuts and legumes, and gut bacteria make more of it, so running short is uncommon. Thinning hair is one of its vaguer early signs. Where it does happen there is usually a reason: long-term antibiotics, chronic anticonvulsants, or intravenous feeding without added biotin.
The caveat · No number on how rare
A clinical reference chapter rather than primary research: it synthesises rather than measures, and puts no number on how rare rare is. The at-risk list is qualitative, with no estimate of how much any of those exposures raises the risk. These chapters are revised continuously, and this reflects the text as it stood in September 2025.