Count: 0 — No vitamins start with Q. The officially recognized vitamins are A, the B-complex (individual B vitamins such as B1, B2, B3, B5, B6, B7, B9, B12), C, D (D2 and D3), E, and K (K1 and K2). Note that several well-known compounds contain the letter Q or the word “quinone” — for example, ubiquinone (CoQ10) and menaquinone (vitamin K2) — but none of these create a standalone vitamin whose name begins with the letter Q.

Recognize why this search returns no results. Vitamin names arose from historical discovery and chemical classification, so they follow letters and numbering assigned by nutrition science rather than the full alphabet; the letter Q was never used as a primary vitamin designation. If you meant related compounds, check ubiquinone (CoQ10) — an important quinone-like supplement that is not classified as an essential vitamin — or menaquinone, which is a form of vitamin K but begins with M. Consult authoritative sources such as the NIH, EFSA, WHO, and USDA FoodData Central for accurate definitions, RDIs, and food-source information.