The opening words of a novel are acknowledged to be among the most important of the book, my own favorite being Chesterton’s “The human race, to which so many of my readers belong.…” But rivaling these words for impact are those of the Methods section of the abstracts of two papers in a recent edition of the New England Journal of Medicine. The first was “We studied 102,216 adults from 18 countries,” surely the the equal of, say, “There was no possibility of going for a walk that day” (Jane Eyre). The second, by the same authors, was “We obtained morning fasting urine samples from 101,945 persons in 17 countries,” again easily the equal of “It was the best of times, it was the worst of times” (A Tale of Two Cities).
However, this was science, not literature. The object of the papers was to cast light on the association, long noted, between sodium intake in the diet and high blood pressure, and to help decide whether a reduction in the sodium intake of entire populations would be a worthwhile public health measure. High blood pressure is one of the principle causes of stroke and heart attack, which are themselves one of the principle causes of death in the world.
The accompanying editorial to the two papers begins with the following words:
Hypertension is the most common modifiable risk factor for cardiovascular disease and death. Worldwide, it is estimated that more than 1 billion adults have hypertension, that this figure is projected to climb to 1.5 billion by the year 2025, and that hypertension accounts for more than 9 million deaths annually.
Let us briefly consider the import of these words. A person with hypertension has roughly one in a hundred chance of dying of his hypertension annually, or one in ten over ten years. But only a sixth of the world’s population has hypertension: therefore the chances are one in six hundred and one in sixty for the population as a whole.
Let us assume that modifying the diet of the population reduced the incidence of hypertensive death by ten percent, a very optimistic assumption. This means that doing so will reduce the chances of the population as a whole dying of a hypertensive disease to one in six thousand over a year and one in six hundred over ten years. In absolute figures, the number of lives saved will be 1,000,000 over one year or 10 million over ten years. This is a lot of lives, but on the other hand altering the diet of the entire population of the world is no small undertaking, and would require (how can I put it delicately?) a considerable infrastructure of authority. In short, there would have to be a World Salt Police.
In fact, the editorial did not advocate a reduction in the world intake of salt, but not on the grounds of the above reasoning. It failed to do so because the evidence of the connection between a high salt intake and high blood pressure was revealed by these papers to be equivocal and non-linear. It was strong for very high salt intakes, but less strong and rather unreliable for lower intakes. Moreover, the measures of salt intake used in these giant, almost hubristic papers (“We studied 102,216 people” indeed!) are not universally accepted as being true reflections of salt intake.
The conclusion is that more research is necessary (it always is). However, there will probably be some enthusiasts who will say that we already know enough about the world dietary salt crisis to act, which means to legislate, survey and police.