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By Root 1985 0

detrimental if consumed excessively.* Others are also unnecessary but far more benign, of which the most notable is gold. That is why gold can be used as a filling for teeth: it doesn’t do you any harm. Of the rest, some twenty-two elements are known or thought to be of central importance to life, according to Essentials of Medical Geology. We are certain about sixteen of them; the other six we merely think are vital. Nutrition is a remarkably inexact science. Consider magnesium, which is necessary for the successful management of proteins within the cells. Magnesium abounds in beans, cereals, and leafy vegetables, but modern food processing reduces the magnesium content by up to 90 percent—effectively annihilates it. So most of us are not taking in anything like the recommended daily amount—not that anyone really knows what that amount should be. Nor can anybody specify the consequences of magnesium deficiency. We could be taking years off our lives, or points off our IQ, or the edge off our memory, or almost any other bad thing you care to suggest. We just don’t know. Arsenic is similarly uncertain. Obviously, if you get too much in your system you will very quickly wish you hadn’t. But we all get a little arsenic in our diets, and some authorities are absolutely certain it is vital to our well-being in these tiny amounts. Others are not so sure.

Which brings us back, in a very roundabout way, to salt. Of all the minerals, the most vital in dietary terms is sodium, which we mostly consume in the form of sodium chloride—table salt.* Here the problem is that we are getting not too little, but possibly way too much. We don’t need all that much—200 milligrams a day, about what you would get with six or eight vigorous shakes of a salt cellar—but we take in about sixty times that amount on average. In a normal diet it is almost impossible not to overload on sodium, because there is so much salt in the processed foods we eat with such ravenous devotion. Often it is heaped into foods that don’t seem salty at all—breakfast cereals, prepared soups, and ice cream, for instance. Who would guess that an ounce of cornflakes contains more salt than an ounce of salted peanuts? Or that the contents of one can of soup—almost any can at all—will considerably exceed the total daily recommended salt allowance for an adult?

Archaeological evidence shows that once people settled down in agricultural communities they began to suffer salt deficiencies—something that they had not experienced before—and so had to make a special effort to find salt and get it into their diet. One of the mysteries of history is how they knew they needed to do so, because the absence of salt in the diet awakes no craving. It makes you feel bad and eventually it kills you—without the chloride in salt, cells simply shut down like an engine without fuel—but at no point would a human being think: “Gosh, I could sure do with some salt.” So how they knew to go searching for it is an interesting question, particularly as in some places getting it required some ingenuity. Ancient Britons, for instance, heated sticks on a beach, then doused them in the sea and scraped the salt off. Aztecs, by contrast, acquired salt by evaporating their own urine. These are not intuitive acts, to put it mildly. Yet getting salt into the diet is one of the most profound urges in nature, and it is a universal one. Every society in the world in which salt is freely available consumes, on average, forty times the amount needed to sustain life. We just can’t get enough of the stuff.

Salt is now so ubiquitous and cheap that we forget how intensely desirable it was once, but for much of history it drove men to the edges of the world. Salt was needed to preserve meats and other foods, and so was often required in vast quantities: Henry VIII had twenty-five thousand oxen slaughtered and salted for one military campaign in 1513. So salt was a hugely strategic resource. In the Middle Ages caravans of as many as forty thousand camels—enough to form a column seventy miles long—conveyed salt across