Vitamins Come from Living Things

Every vitamin is made by living cells — either our own, or in other species. Vitamin D is produced in our skin, for example, when sunlight strikes a precursor of cholesterol. A lemon tree makes vitamin C out of glucose. Making a vitamin is often an enormously baroque process. In some species, it takes 22 different proteins to craft a vitamin B12 molecule. While a protein may be made up of thousands of atoms, a vitamin may be made up of just a few dozen. And yet, despite their small size, vit...