Count: 0 — No vitamins start with the letter Y. The recognized vitamin set worldwide consists of vitamin A, the B-complex vitamins (each listed individually), vitamin C, vitamin D (D2 and D3), vitamin E, and vitamin K (K1 and K2). The historical naming system and modern nutrient definitions leave no officially recognized vitamin whose name begins with Y.

Note the reason: vitamins are named by discovery, chemistry, or function, and the early alphabetical labels stopped with K while the complex B group received numbered and chemical names. Authoritative authorities such as the NIH, WHO, EFSA, and USDA list the same set of vitamins and show no entry for a “Y” vitamin. Treat vitamins as essential organic micronutrients that meet strict biochemical and deficiency criteria; nothing identified to date fits those criteria under a Y name.

Remember that several substances begin with Y but are not vitamins. Tyrosine (single-letter code Y) is an amino acid, not a vitamin. Yohimbine and yeast-derived compounds have biological effects but do not meet vitamin definitions. Consult standard vitamin lists (A–K and the B-complex) for benefits, primary food sources, and RDIs from NIH, WHO, EFSA, and USDA when you need authoritative nutrient guidance.