At Home - Bill Bryson [91]
Meanwhile, it turned out that Funk’s vitamines were not nearly as coherent a group as originally thought. Vitamin B proved to be not one vitamin but several, which is why we have B1, B2, and so on. To add to the confusion, vitamin K has nothing to do with an alphabetical sequence. It was called K because its Danish discoverer, Henrik Dam, dubbed it Koagulations vitamin for its role in blood clotting. Later, folic acid (sometimes called vitamin B9) was added to the group. Two other vitamins—pantothenic acid and biotin—don’t have numbers or, come to that, much profile, but that is largely because they almost never cause us problems. No human has yet been found with insufficient quantities of either.
The vitamins are, in short, a disorderly bunch. It is almost impossible to define them in a way that comfortably embraces them all. A standard textbook definition is that a vitamin is “an organic molecule not made in the human body which is required in small amounts to sustain normal metabolism,” but in fact vitamin K is made in the body, by bacteria in the gut. Vitamin D, one of the most vital substances of all, is actually a hormone, and most of it comes to us not through diet but through the magical action of sunlight on skin.
Vitamins are curious things. It is odd, to begin with, that we cannot produce them ourselves when we are so very dependent on them for our well-being. If a potato can produce vitamin C, why can’t we? Within the animal kingdom only humans and guinea pigs are unable to synthesize vitamin C in their own bodies. Why us and guinea pigs? No point asking. Nobody knows. The other remarkable thing about vitamins is the striking disproportion between dosage and effect. Put simply, we need vitamins a lot, but we don’t need a lot of them. Three ounces of vitamin A, lightly but evenly distributed, will keep you purring for a lifetime. Your B1 requirement is even less—just one ounce spread over seventy or eighty years. But just try doing without those energizing specks and see how long it is before you start to fall to pieces.
The same considerations exactly apply with the vitamins’ fellow particles the minerals. The fundamental difference between vitamins and minerals is that vitamins come from the world of living things—from plants and bacteria and so on—and minerals do not. In a dietary context, minerals is simply another name for the chemical elements—calcium, iron, iodine, potassium, and the like—that sustain us. Ninety-two elements occur naturally on Earth, though some in only very tiny amounts. Francium, for instance, is so rare that it is thought that the whole planet may contain just twenty francium atoms at any given time. Of the rest, most pass through our bodies at some time or other, sometimes quite regularly, but whether they are important or not is still often unknown. You have a lot of bromine distributed through your tissues. It behaves as if it is there for a purpose, but nobody yet has worked out what that purpose might be. Remove zinc from your diet and you will get a condition known as hypogeusia, in which your taste buds stop working, making food boring or even revolting, but until as recently as 1977 zinc was thought to have no role in diet at all.
Several elements, like mercury, thallium, and lead, seem to do nothing good for us and are positively