Salt may be a health issue now but the two most famous salt
wars involved the City of Perugia versus Pope Paul III over a salt tax
introduced by the Vatican in 1540 and then the Mexican-US salt wars or El Paso
salt wars of 1877 over ownership of salt rich lakes in Texas. Today’s salt war is
fought on the plains and hills of public health nutrition and is put under the
microscope in a series of papers in the International Journal of Epidemiology. The
central paper, from researchers at Boston and Columbia Universities, examines
the objectivity of both camps in this public health feud[1].
It began with a search of the scientific literature for all
reports relating salt to health. A total of 269 such reports were found of
which two thirds were simply comments or letters in learned journals, a quarter
were primary studies in which the hypothesis of a salt health link was directly
tested in humans and the remaining 9% were either guidelines or reviews of
primary data (systematic reviews). Of
this body of evidence, 54% supported a link between salt and health, 33% were
contradictory of such a relationship and 135 were inconclusive.
The authors used this large data set to answer a number of
questions. The first was to analyse the data to ascertain if a bias in citation
of scientific paper existed. By that is meant the following: Is an author who
supports one side or other of the hypothesis more like to cite other studies
supporting their stance and less likely to pay attention to studies which are
at variance with their stance. The answer to that question is emphatically,
yes. Those supporting the salt health link were twice as likely to prefer to
cite similar supporting articles. Among those who contradict the salt-health
hypothesis, they were three times more likely to cite contradictory than
supportive papers and among those who were inconclusive, the bias factor was
all of 15 fold. What this means is that scientists in this field are very
definitely not objective in their view of the problem and presumably its solution.
A second question was the extent to which the literature is dominated by a
small or large body of papers. In fact, the authors found that a small number
of authors and a few reports do, in fact, dominate the debate. Thirdly the
authors sought to see if there was consistency in the selection of primary
research data. In fact there wasn’t. Primary data, which are the hub of
objectivity, were selected according to the prevailing bias of each camp.
John Ioannidis from Stanford University was asked to not only
write a comment but to seek similar comments from those in the field[2].
He immediately encountered the dogmatism that dominates public health
discussion. One invitee who declined to add a commentary wrote thus: “ the
paper ….is rubbish…there doesn’t seem to be any realization that the majority
of those papers that are against salt reduction are funded by the food or salt
industry, just like the tobacco industry did (or still does for that matter)
for cigarettes….I wouldn’t have anything to do with it.” This belief that
scientific bias is a function of industry funding is very naïve. Those who live
in the EU will be familiar with the requirement in the majority of research
funding, that industry involvement is a must. Without it, the grant doesn’t
even get to review. The logic is that such research will generate knowledge,
create jobs and lead to economic growth. “Blue skies” research is funded with
no industrial requirement but this is a small fraction of the research spend.
Society makes the rules and scientists play the game according to those rules.
The philosopher Thomas Kuhn understood the way science works.
He pointed out that it exists as “normal” science or “revolutionary” science.
Revolutionary science is a rare occurrence such as the discovery of the double
helical nature of DNA and its transforming effect on our knowledge of cell
division. Normal science is the antithesis of revolutionary science and it
utterly dominates the scientific landscape. So scientists “defend” the
paradigms of normal science and continue to do so until, from nowhere, emerges
some new revolutionary finding, which, forever, changes the science landscape.
- In the
salt and health war, honest scientists have for one reason or another
looked at the landscape and decided to support or contradict the thesis.
Or did they? Is it possible that they first opted for one side or the
other, and then sought the scientific basis to support these views? The
Nobel Laureate in economics Daniel Kahneman would argue the latter. He points
out that our brain operates the decision making process in two systems.
- System
1: Fast, automatic, frequent, emotional, stereotypic,
subconscious
- System
2: Slow, effortful, infrequent, logical, calculating, conscious
System 2 decides first on which side of the
salt (and general health) debate we reside. System 1 now bolsters this with
analytical data.
Ioannidis argues that the scientific morass
of salt and health cannot be resolved by reviewing the existing data no matter
how fancy the statistical approach of that review might be. Primary data, which
studies real human beings in real life settings, are what counts. As he points
out, the design of real primary studies can be such as to more likely to lean
in one direction than another. The loser
is Joe Soap who eventually does what the US electorate is presently doing. They
will cry: ”A plague on both your houses” and go their own way. Scientific
dogmatism is destroying science. Dissent is the oxygen of science and to
belittle it and its proponents, as “industry hacks” is sad. These days the
noisiest and most vociferous media friendly scientists win.
More on this in my new book: ”Ever seen a
fat fox ~ Human obesity explored” due out in early May
