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One of the food industry's arguments against sodium labeling involves the somewhat equivocal nature of the medical case against salt. As with smoking and cancer, cholesterol and heart disease, it is difficult to prove direct cause and effect.
Statistically the link is clear. In countries where sodium intake is high, so is the frequency of hypertension. Japan is the most striking example. With a diet based largely on fish, pickled vegetables and soy sauce (1,029 mg sodium per tablespoon), the average Japanese citizen consumes nearly three teaspoons of salt a day. In the northern agricultural provinces, where salt is still widely used as a preservative, six teaspoons or more a day is not uncommon. And what is probably the highest sodium diet in the world coincides with what seems to be the world's highest rate of hypertension; in some villages fully 40% of the residents have high blood pressure. No national statistic for hypertension is available for Japan as a whole, but until last year, stroke was the country's leading cause of death.
Japan and the U.S., however, are both complex societies where citizens are subject to all sorts of variables, including stress, that could contribute to hypertension. More convincing evidence against sodium conies from simpler cultures, where it is still possible to find people living relatively simple lives on low-salt diets. The tribesmen in New Guinea, the Amazon Basin, the highlands of Malaysia and rural Uganda all eat very little salt. Hypertension is virtually unheard of in those regions, and the blood pressure of individuals does not rise steadily with age, as it does in the U.S. and other salt-loving nations. But when salt is introduced into a salt-free culture, blood pressure climbs.
In a classic study, Dr. Lot Page headed up a Harvard team that from 1966 to 1972 studied six tribes in the Solomon Islands. Three were totally unaffected by Western culture and three, otherwise very "primitive" (no roads, no telephones, no pollution), got to eat salt-heavy canned ham and beef jerky supplied to them by Chinese traders. Only in the second group did blood pressure increase with age. It was highest in the tribe that traditionally cooked its fish and vegetables in sea water. The tribes did not differ in weight or any other medically significant way. Says Page: "When we analyzed all the components of change, diet always showed up as the key factor."
Lowering salt intake seems to reduce hypertension too. Beginning in 1972, Dr. John Farquhar of Stanford University conducted a three-year study of 1,500 men and women selected at random in three California towns. In two of the towns, subjects cut salt intake 30%. In the third, no dietary change was made. The result: blood pressure was 6.4% lower among the low-salt people than in the control town.