The History and Politics of Salt

Two books that I have recently enjoyed deal with the historical and political aspects of salt, the use and veneration of which is nearly as old as civilization itself. The first is called Salt, Diet, and Health, and is written by two of the leading advocates of salt restriction, Graham MacGregor and Hugh de Wardener. ¹ It discusses not only the medical aspects of salt, but more interestingly, also the historical and political aspects. The second is Salt: A World History, by Mark Kurlansky, a writer and historian. ² Salt has played a major role in the fortunes of many societies. Although it originally became important because of its ability to preserve food (particularly meat and fish), it assumed a symbolic significance that was disproportionate to its economic value. In western societies the saltcellar was traditionally a symbol of friendship and hospitality, and Japanese sumo wrestlers sprinkle salt on the ground to sanctify it before a contest.

In the 13th century Venice was the largest city in Europe, and the Venetians attributed their success to their ability to export salt to the surrounding cities. Not only were they able to extract it from the shallow lagoons surrounding the city, but Venetian exporters were required to bring back salt when they returned to Venice, for which they were paid a subsidy. Salt was then resold by the Republic at a profit. According to Kurlansky, salt accounted for nearly 50% of Venetian imports between the 14th and 16th centuries. The Venetian salt administration was effectively a clearing bank that contributed to the costs of defending and maintaining the city in all its splendor. Like OPEC's (the Organization of Petroleum Exporting Countries) handling of oil some hundreds of years later, Venice was able to maintain the price of salt by restricting the supply. In the 13th century the Venetians shut down the salt works in Crete, and paid off the local workers in order to keep their monopoly.

In France, a salt tax was introduced as early as the 13th century, but it varied widely from one part of the country to another, and smuggling salt across the borders of different regions became a capital offense. Cardinal Richelieu stated that the salt tax was as valuable to France as the American silver mines were to Spain. In the United States, the federal government imposed a tax on imported salt in 1797, which was soon repealed, but reimposed in 1814 as a war tax. It was eventually abolished in 1894. During the Civil War the South was short of salt, and General Sherman ordered salt to be declared as contraband on a par with gunpowder “because of its use in curing meats without which armies cannot be subsisted.” ¹ The Union effectively blocked the Southern ports to prevent salt from being imported, and also destroyed the coastal saltworks. By 1863 the price of salt in the South had increased by more than 50 times over its prewar level.

One of the most dramatic political uses of salt was made by Mahatma Ghandi in his quest for the independence of India from the British. For many hundreds of years India had a plentiful and cheap supply of salt, most of it coming from saltpans on the two coasts, Orissa in the East, and Gujarat in the west. The British had a salt industry of their own, but economically it could not compete with the Indian supply. So in the 19th century they took over both sources, and introduced a salt tax. This meant that it was illegal for Indians to gather salt from the beaches of Gujarat and Orissa. In 1930 Ghandi announced to the Viceroy of India that he was going to lead a march to the coast of Gujarat, which he subsequently did. He was initially accompanied by 78 followers, but when they reached the sea after 25 days of marching, this number had swelled to several thousand. On April 5th, 1930 Ghandi publicly broke the British salt law by bending down and scooping up a handful of salt. This was followed by similar actions in Orissa, and the police made hundreds of arrests, which eventually included Ghandi. This set off protests all over India, and was the beginning of the national independence movement. The salt laws were in fact repealed 1 year later, and salt gathering became legal again, but the damage had been done, and India eventually achieved full independence in 1947.

Given its long history in the political and economic arenas, the recent controversy and publicity about salt and health seems not so surprising. One section of MacGregor and de Wardener's book is called “The Industrial Conspiracy,” and describes the current actions of the food industry to promote salt. In the United Kingdom this has been organized by the Salt Manufacturers' Association, and in the United States by the Salt Institute, a public relations organization supported by the manufacturers. There are three main commercial reasons for promoting the greater use of salt in foods. The first is the improvement of taste, with which few people would argue, although this May be the result of our addiction to salt rather than any intrinsic need for it. This point has been argued most forcibly by Denton, ³ who induced hypertension in chimpanzees by feeding them a high‐salt diet, and then reverted them to low salt, at which point they refused to eat and lost weight. The other two reasons for promoting salt intake are both subtler and more blatantly commercial. One is that the salt content of food determines the water content, and hence the weight; adding salt thus increases the weight of food at very little cost. This is nothing new, and in the 19th century cattle drivers who were taking their cattle to market in Poughkeepsie, NY used to stop at a place called Salt Lick on the day before they reached the market, where the cattle would take on salt and water, thereby increasing their weight and market value. The third reason is the stimulation of thirst: bars that offer salted peanuts and potato chips do so not from any altruism, but because people will order more drinks.

The issue of salt as a cause of high blood pressure and cardiovascular disease has been controversial until recently, because of claims that salt has little effect on the blood pressure of the majority of people, and also one much‐publicized claim by Alderman et al. ⁴ that consuming a low salt diet May actually increase the risk of cardiovascular morbidity. The activities of the Salt Institute, while usually behind the scenes, became manifest to the medical profession in an article refuting the findings of the Intersalt study published in the British Medical Journal in 1996. ⁵ Intersalt was a massive cross‐sectional survey of salt intake and blood pressure of 10,074 men and women in 32 countries. ⁶ The main finding was a positive relationship between the two, with an increased effect of salt on blood pressure in older people. The Salt Institute paper made an unsuccessful attempt using convoluted statistics to discredit this, and was prefaced by a statement from the BMJ that “we have published this paper from the Salt Institute because it is an interesting example of how special interest groups use data to advance their position.” In an accompanying editorial Law ⁷ wrote: “This analysis is of service only to illustrate the lengths to which a commercial group will go to protect its market when presented with clear evidence detrimental to its interest.” The Salt Institute web site (www.saltinstitute.org) makes for interesting reading. There is a section on salt and cardiovascular health, which states that the National Academy of Sciences recommends that Americans should consume a minimum of 500 mg/day of sodium to maintain good health. The recommended upper limit is not mentioned, but there is a statement that “every substance, including water, can be toxic in certain concentrations and amounts; this is not a significant concern for dietary salt.” The thrust of the Salt Institute's argument is that blood pressure itself is not very important, and that what we need to focus on is the relationships between salt intake and disease outcomes. Hence the statement that “there is no evidence that reducing dietary sodium improves the risk for heart attacks or strokes for the general population.” Strictly speaking, this is true, and is likely to remain so, since a population‐based study of the effects of salt restriction on cardiovascular morbidity will almost certainly never be done. But to ignore the effects of salt on blood pressure is surely not in the best interests of our patients and the general public.

One of the traditional criticisms of the salt‐isharmless school was that there has been no convincing evidence that the amount of salt in the diet actually does affect cardiovascular morbidity, and hence the Alderman et al. study mentioned above ⁴ that claimed the reverse had great import. It was a retrospective analysis of the first National Health and Nutrition Examination Survey (NHANES‐1) data collected between 1971 and 1975, and found that subjects reporting a low‐salt diet were at increased risk of cardiovascular disease mortality at follow‐up. ⁴ However, a second examination by He et al. ⁸ of the same cohort came to different conclusions. No relation between salt intake and morbidity was found in the nonoverweight participants, but in those who were overweight there was a positive relationship between salt intake and mortality from both strokes and heart attacks. It is worth considering why two studies looking at the same database and trying to answer the same questions can come to such different conclusions. First, the number of subjects included in the Alderman et al. analysis was bigger—11,346 as opposed to 9485 in the He et al. study—because the latter excluded people who had been on low salt intakes at baseline, and also those with a history of known cardiovascular disease. Both studies examined salt intake in relation to total calorie intake. The Alderman et al. study came up with the rather hard to interpret finding that mortality was negatively related to sodium intake, but positively related to sodium‐to‐calorie intake. He et al. found positive relationships for both sodium and sodium‐to‐calorie intake. One of the problems with this type of retrospective study is that there was no way of knowing why people were consuming a low‐salt diet, and it is quite probable that many of them had been advised by their physicians to cut back on their salt intake. Alderman et al. attempted to control for this by including a history of hypertension and cardiovascular disease in their analysis, but this May have been inadequate. The finding in the He et al. analysis of a positive relationship between salt intake and morbidity in the obese certainly makes sense, because there is extensive evidence that obese people are more salt sensitive than their lean counterparts.

Since then, a Finnish study ⁹ also showed a positive relation between high salt intake and coronary heart disease in men over an 8–13‐year follow‐up period, and a Japanese study ¹⁰ found a relationship with strokes, but not coronary heart disease. This latter finding is not surprising since coronary heart disease is still relatively uncommon in Japan. The Intersalt study also reported an association between salt intake and stroke incidence. ¹¹ In contrast, no relation between urinary sodium and coronary heart disease morbidity was seen in the Scottish Heart Health Study. ¹² In all, there is a general consistency in these results, given the fact that many of them were based on a single 24‐hour urine collection to estimate sodium intake, a measure which has repeatedly been found to have a very low reproducibility, and the interval between the urine collection and the cardiovascular event might be as long as 20 years.

The effects of salt intake on blood pressure were hopefully definitively resolved by the Dietary Approaches to Stop Hypertension (DASH)‐sodium study, ¹³ in which subjects who were either eating a typical American diet or the DASH diet were allocated to three levels of salt intake. It confirmed that changing salt intake does affect blood pressure to a substantial extent. One of the major features of this study was that people were provided with all their meals while in the study, so there was a very high assurance that they were actually consuming the correct amounts of sodium.

The great salt debate has attracted more publicity than it deserves. There can be no question that most of us eat far more salt than we need, and also that for hypertensive patients, cutting down on salt intake is much more likely to benefit than to harm them. However, any national or international recommendations on eating habits should not focus on a single ingredient such as salt, but rather encourage people to eat more healthy foods, such as fruits and vegetables. We should not forget that most of the salt we eat comes not from the saltshaker, but from the food we buy in the supermarket.