The Man Who Ate Everything - Jeffrey Steingarten [88]
The Yanomami differ from Americans in many ways besides salt. They are very skinny, they drink absolutely no alcohol, they are geographically isolated and therefore genetically distinct, and they get lots of exercise under the lush leafy canopy of their Brazilian rain forest, where automobiles are extremely scarce. The Solomon Islanders used to be almost as popular among salt phobics as the Yanomami—until they were brought into the modern age and their blood pressure rose. But this was not attributable to salt. Obesity and lack of exercise were identified as the causes.
It was while contemplating the vacuous taste of an unsalted potato chip that I decided to read through the medical research about salt and hypertension from the past decade or so and find out why America’s public-health establishment gets so steamed up about it. Having done so, I still can’t understand what the fuss is all about. The animal studies are completely inconclusive—some animals are sensitive to salt; others are resistant; some get high blood pressure when they are stressed; others do not. One research group managed to raise the blood pressure of healthy laboratory rats only by feeding them an 8-percent-salt diet, the equivalent of two cups a day for you and me. Clinical studies with human beings have never shown that salt can cause hypertension in healthy people. At worst, salt can exacerbate hypertension in some of those already afflicted with it.
Nineteen eighty-eight was the year of the great salt showdown, the massive and rigorous Intersalt study. Fifty-two centers were established in thirty-two countries around the world, from Argentina to Zimbabwe (the Yanomami were included, of course, along with three other isolated Stone Age peoples), and 10,079 subjects in all were tested. Each was measured for a small number of variables: blood pressure, sodium and potassium excretion (which in healthy people is an accurate measure of sodium and potassium intake), age, alcohol use, height, and weight. All urine samples were flown to a central lab in Belgium; some samples were split in two and tested separately, and the results were compared to gauge the lab’s consistency. All measurements were sent to London, entered twice into a computer, and the double entries compared to ensure accuracy. Never before has such care been taken in a blood pressure study of this size and geographic scope. Funding came from the World Health Organization, heart associations around the world, the U.S. government, and a British foundation.
The results were extremely distressing to those who had hoped to prove a link, once and for all, between salt and blood pressure. The four hunter-gatherer cultures did show extremely low salt excretion and extremely low blood pressure. But the researchers could find no significant link in the rest of the world between salt and hypertension.
The Yanomami eat bananas and starchy roots all day; you need to go to such extremes to lower your blood pressure through diet. Nearly everybody in the modern world eats between 2 and 5 grams of sodium a day (1 to 2½ teaspoons of salt). Tinkering with your salt intake in this range will not affect your blood pressure. As the Harvard Medical School Health Letter concluded about the Intersalt study: “It seems unlikely that salt intake is a major influence on the development of hypertension in most of the world’s populations.”
Obesity and alcohol intake are strongly associated with high blood pressure; you can do yourself a great favor by losing weight and drinking less if blood pressure is a problem. And Intersalt did show that the more salt people eat, on average, the more likely it is that their blood pressure will increase as they grow older. But the numbers are unimpressive. If everybody in America slashed his or her salt consumption from eight grams a day to two, the average blood pressure would go down by only 2 percent.
Some people are extremely sensitive to salt; their blood pressure goes way up when they eat it and