For almost 100 years, some scientists have been warning about the harmful effects of salt in our diets. For the last 40 years or so that has also been the “consensus” view of the medical/regulatory establishment. It was “settled science” we were told. There was complete “consensus” within the medical world it was proclaimed.
Salt was evil.
But apparently the “settled” science was not quite so settled after all. The “consensus” was nothing more than “group think”. In the words of the Wall Street Journal:
Yet the latest USDA food pyramid, which was updated as recently as 2011, clings to simplistic low-salt pseudo-science. The FDA is pressuring food manufacturers and restaurants to remove salt from their recipes and menus, while the public health lobby is still urging the agency to go further and regulate NaCl as if it were a poison.
The larger point is that no scientific enterprise is static, and political claims that some line of inquiry is over and “settled” are usually good indications that real debate and uncertainty are aboil. In medicine in particular, the illusion that science can provide some objective answer that applies to everyone—how much salt to eat, how and how often to screen for cancer, even whom to treat with cholesterol-lowering drugs, and so on—is a special danger.
It is not so easy now to retrace exactly how the salt scare developed and became part of the establishment view. Certainly Lewis Dahl of the Brookhaven National Laboratory was one of the key actors who spread the alarm. He was well placed within US Government circles and soon rather dubious and alarmist conclusions became part of the “establishment view”. Pseudo science became “settled science”:
In 1904 French doctors reported that six of their subjects who had high blood pressure—a known risk factor for heart disease—were salt fiends. Worries escalated in the 1970s when Brookhaven National Laboratory’s Lewis Dahl claimed that he had “unequivocal” evidence that salt causes hypertension: he induced high blood pressure in rats by feeding them the human equivalent of 500 grams of sodium a day. (Today the average American consumes 3.4 grams of sodium, or 8.5 grams of salt, a day.)
Dahl also discovered population trends that continue to be cited as strong evidence of a link between salt intake and high blood pressure. People living in countries with a high salt consumption—such as Japan—also tend to have high blood pressure and more strokes. But as a paper pointed out several years later in the American Journal of Hypertension, scientists had little luck finding such associations when they compared sodium intakes within populations, which suggested that genetics or other cultural factors might be the culprit. Nevertheless, in 1977 the U.S. Senate’s Select Committee on Nutrition and Human Needs released a report recommending that Americans cut their salt intake by 50 to 85 percent, based largely on Dahl’s work.
Thereafter “group think” took over. Consensus opinion – and not objective science – ruled. Now we are finding out that there is no clear evidence that salt is harmful and there is some evidence that too little salt is dangerous and can increase the risk of heart disease.
In April 2010 the Institute of Medicine urged the U.S. Food and Drug Administration to regulate the amount of salt that food manufacturers put into products; New York City Mayor Michael Bloomberg has already convinced 16 companies to do so voluntarily. But if the U.S. does conquer salt, what will we gain? Bland french fries, for sure. But a healthy nation? Not necessarily.
This week a meta-analysis of seven studies involving a total of 6,250 subjects in the American Journal of Hypertension found no strong evidence that cutting salt intake reduces the risk for heart attacks, strokes or death in people with normal or high blood pressure. In May European researchers publishing in the Journal of the American Medical Association reported that the less sodium that study subjects excreted in their urine—an excellent measure of prior consumption—the greater their risk was of dying from heart disease. These findings call into question the common wisdom that excess salt is bad for you, but the evidence linking salt to heart disease has always been tenuous.
It has taken 40 years for this alarmist meme that salt is harmful to be brought down to earth. Group-think and “consensus science” has its own inertia which makes it difficult to overturn what becomes matters of faith rather than of evidence.
And just a few days ago another establishment paper created headlines when it stated that salt “causes 1.65 million deaths every year across the globe. A published study in New England Journal of Medicine on Thursday, found that an average consumed salt (sodium) per day is twice the amount recommended by the World Health Organization. A 3.95 gm consumption per day beyond the recommended amount of 2 gm”. But all they actually did was measure/estimate salt consumption and then multiplied that by an assumed death rate. By the time the headlines were written a simple measurement of salt consumption became evidence of the dangers of salt! That’s consensus science!
The 1970s and 80s saw many such alarmist memes – based on little and dubious science – become the “consensus view” and the “politically correct” faith to be followed. It was the time when the nonsensical “Limits to Growth” became the bible of the day. It was the time of the DDT scare where the disadvantages were blown out of all proportion and the subsequent ban has been a case of “throwing the baby out with the bath water. Natural variations of the ozone hole were taken to be due to the human use of fluorocarbons. Acid rain was going to kill all the forests.
Whenever I now hear that some science is “settled” or that there is a consensus around some “belief” – as with climate science today – I am inclined to view the claims with a very large bushel of salt.
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