Unfortunately, if you’ve delved into the scientific literature, you
know that “facts” are rarely as black and white as we’d like them to be,
that science and facts often require interpretation, and that true
consensus within any topic takes decades—sometimes centuries—and is
preciously rare.
In the meantime, people are suffering and dying from illnesses that
science, eventually, might show us how to prevent. It is understandable
that those within the research community and those in public policy feel
compelled to act—to “do something”—now with what we think we know today.
However, what we thought we knew often proves to be inaccurate. This
may be what happened with the commonly-held belief that lower sodium
diets are always healthy, as I detail in my new CEI study, “Shaking up the Conventional Wisdom on Salt: What Science Really Says about Sodium and Hypertension,” published this week.
If you ask 10 people on the street what they think about salt’s role in human health, more than eight out of 10
will likely give some variation of the “salt dogma”—they’ll reveal some
level of belief in the idea that lowering sodium will reduce blood
pressure and improve health. A year ago, I might have been among them.
But, despite what many in the public health field would have us believe,
this consensus is not shared by those within the research community. As a study published last
year demonstrated, only about half of those in the field believe there
is evidence to support population-wide sodium reduction (policy attempts
to get us all to lower salt consumption).
In addition to the shakiness of the current dogma, the most shocking
findings from my research were how polarized the experts are on this
issue and why our fervent belief in the evils of sodium has stuck around
for 40 years, despite ever-increasing evidence to the contrary.
The intense, vitriolic, and largely ideological war that has been
raging over salt for more than a century can be broken out into two
camps:
Camp 1 believes the
science irrefutably shows higher sodium leads to higher blood pressure,
and therefore getting the general population to lower consumption to the
government-recommended limit would result in lower blood pressure and
better health outcomes.
Camp 2 is skeptical that
salt is the main driver of hypertension or that sodium restriction is
the best way to improve health outcomes for broad swaths of the
population.
Whenever anyone from Camp 2 publishes a study, members of Camp 1
invariably criticize the study, and vice versa. Accusations range from
the typical “methodological flaws” argument to the more inflammatory
“industry influence” charge. Often, claims are made that the
preponderance of “good” evidence points strongly enough one way or the
other that action is justified.
Wading into this gang war, I expected CEI’s study to receive criticism from one side or the other (if not both). And, lo and behold, the American Heart Association
(AHA)—which advocates for an even lower level of sodium than even the
government recommendation—was the first to come out against it. What was
surprising and instructive was the study the AHA cited as evidence of
the wisdom of population-wide sodium reduction.
The research, published this month in the British Medical Journal
(BMJ), details the cost effectiveness of implementing strategies to
reduce population sodium—like the “voluntary” sodium reductions for food
manufacturers the Food and Drug Administration proposed last year.
While presented as “proof,” this study is little more than an exercise
in fantasy.
The researchers assume a linear, dose-response relationship between
dietary sodium and blood pressure—meaning that for every increase in X
mg of sodium there’s a corresponding X increase in blood pressure. They
also assume that for every increase in blood pressure, there’s a
corresponding increase in deaths. Lastly, they assume programs that
nudge people to reduce their sodium will work. Thus, if all these
assumptions are correct, the cost of implementing such programs balances
out with the health benefits. The problem is, their assumptions aren’t
supported by the research.
First, it requires little scientific background to realize that any trend between sodium and health cannot be linear. Humans require dietary
sodium in order to live, so there is a low level at which health does
not improve, but becomes worse. In fact, researchers have pointed to
this sub-optimal level of sodium intake as a possible reason for why
several large population studies have found that groups with extremely
low sodium intake are more likely to die (they also found higher risk of mortality at the extreme upper end).
Furthermore, the research the BMJ study’s authors relied upon likely
had skewed results because of the types of people on which they were
based. As noted in our study and elsewhere,
not everyone responds the same way to increases and decreases in
dietary sodium. As Niels Graudal (a Camp 2 researcher) pointed out in
commentary on the BMJ article, randomized control trials—the
gold-standard of biomedical research—“have documented that there is no
effect of blood pressure reduction on health outcomes in normotensives
individuals.”
Salt’s role in hypertension and other aspects of human health is far
from settled. That does not mean that for some people sodium reduction
won’t help, but it does indicate that neither population-wide
recommendations nor “soft regulation” of sodium are warranted by the
existing evidence.
For the past four decades, health agencies have been pushing us to
consume less sodium, even as Americans—and the rest of the world—have
continued to consume roughly the same amount of sodium. This is despite
the fact that processed foods have become saltier and we eat more
processed foods as a culture. That said, the prevalence of hypertension has increased
over the last two decades. These facts should prompt researchers to ask
why this is the case, and to investigate other possible causes and
solutions to hypertension.
Unfortunately, it seems no amount of evidence will stop those who cling to the old dogma. As researcher Sandro Galea put
it: “We pay quite a bit of attention to financial bias in our work … we
seldom pay attention, however, to how long-held beliefs bias the
questions we ask and the results we publish, even as new data become
available.”
But don’t take my word for it. If CEI’s study
proves anything, it’s that health decisions are intensely personal,
that no solution works best for everyone, and that individuals must
decide and test for themselves what health advice is most likely to
benefit them."
No comments:
Post a Comment
Note: Only a member of this blog may post a comment.