In the 1920s, scientists believed that only two vitamins existed. One was fat-soluble, which means it could dissolve in oil or fat. This vitamin the scientists called Vitamin A. The other vitamin was water-soluble; it could dissolve only in water. This, they called Vitamin B.
The fat-soluble vitamins were given letters of their own. But some substances that were given letter names were later found not to be vitamins at all, and were renamed with a word.
For instance, there was once a substance called Vitamin H, but it’s now called biotin. That’s why we have a Vitamin A, B, C, D, E, and K, but no vitamins for the letters F, G, H, and I.
But then scientists began to discover other vitamins. The first was a water- soluble vitamin, so it was named B2. Eventually, most of the water-soluble vitamins were named B, followed by a number. Vitamin C is also water- soluble.
The last vitamin to be discovered was B12, which wasn’t found until 1948!