The first five vitamins, discovered between 1910 and 1920, were named A, B, C, D and E. Interestingly, D had originally been lumped together with A until it was later discovered that two separate factors were involved. When a second similar property to the vitamin originally named B (Thiamine) was discovered in 1920, both were renamed to B1 (Thiamine) and B2 (Riboflavin). The remaining B vitamins were lumped together under the designation “B complex.” Today’s vitamins skip from E to K because substances that were once thought to be vitamins were reclassified. For example, vitamin F is today known as the essential fatty acids Omega 3 and 6. Similarly, vitamin G was reclassified as B2 (Riboflavin), and vitamin H is now Biotin. So, in reality, the vitamins between E and K were never “skipped,” but simply reclassified and renamed.
