DrG's Medisense Feature Article
14051-Dietary_Sodium
Dietary
Sodium: Dogma, Doubt, Delusion and Just What Is Desirable?
by Ann Gerhardt, MD
May 2014
Print Version
Salt (half of which is sodium), health and the 2013 Institute of
Medicine (IOM) report concerning dietary sodium recommendations was the
subject of a major symposium at the April 2014 American Society of
Clinical Nutrition (ASCN) scientific meeting. The Centers for
Disease Control (CDC), recognizing evidence that severe sodium
reduction might harm health, had commissioned the IOM to update
recommendations about sodium intake.
The 2013 IOM report concluded that 1) there is a risk of more
cardiovascular disease with high sodium intake; 2) studies are
inconclusive about the health effect on the general population when
dietary sodium falls below 2300 mg/day (about 2 teaspoons of salt); 3)
sodium restriction below 2300 mg/day is harmful for patients with heart
failure; and 4) there is not enough evidence to determine if people at
high risk for vascular disease should limit sodium intakes to less than
2300 mg/day.
The ASN symposium presenters agreed with the harm of extreme sodium
restriction in heart failure patients, but felt that the IOM’s
conclusions did not go far enough in other people.
Dogma: A substantial body
of evidence, mostly from Westernized societies, links excessive dietary
sodium to hypertension, stroke and heart disease. These studies
assumed, without actual data, that lowering sodium intake all the way
to zero would result in ever lower risk of hypertension (high blood
pressure) and disease.
Bunching together results from many experiments yields an average drop
of 3 to 5 points in the top blood pressure number and a small dip of
0.8 to 2 points in the bottom number. People eating huge amounts
of sodium responded the best, especially if they were obese.
In 2010 the Department of Health and Human Services and the Department
of Agriculture updated the Dietary Guidelines for Americans (DGA) in
response to a general acceptance of the need for sodium
reduction. Their goals were for everyone to eat less than 2300 mg
sodium per day. High risk people were to shoot for a more
stringent goal of 1500 mg/day. People at high risk include
African Americans, those older than 50 years and anyone who already has
hypertension, diabetes or chronic kidney disease.
Dietary sodium currently averages 3400 mg/day in U.S. adults (range
2000-5000). This is an improvement, down 500 mg/day from 10 years
ago, but failure to meet DGA guidelines causes consternation in many
public health officers.
Doubt: Should these
guidelines really apply to everyone? A pile of data show that
there are sodium responders and non-responders. Only a few
people with normal blood pressure drop their pressure in response to
less dietary sodium. Salt-responsiveness may change over the
life-span – For example, salt-sensitivity in some obese
hypertensive teens dissipates with weight loss.
African-Americans as a group retain sodium more than do Caucasians, but
among both groups blood pressure response to sodium is variable and
very dependent on genetics. Salt sensitivity is related to at
least a dozen genes, not all of which have an obvious connection to
sodium and blood pressure.
In the DASH (Dietary Approaches to Stop Hypertension) trial of people
with high blood pressure, a fruit and vegetable-rich prudent diet
slashed the average systolic pressure by 11 points and the diastolic
pressure by 5 points. Unlike the sodium data, the DASH diet
lowered blood pressure in all categories of people. Blood
pressure didn’t drop any further when subjects also limited salt.
Diets low in potassium and calcium foster higher blood pressure.
Salt decreases potassium and calcium levels by increasing urinary
losses. Could this be part of the reason that sodium raises blood
pressure? Should we be focusing more on increasing dietary
potassium and calcium and less on reducing sodium?
Other data suggests that chloride, not sodium, may be the
problem. In animals, non-chloride sodium compounds, such as
sodium glutamate, sodium bicarbonate, sodium ascorbate and sodium
phosphate, do not raise blood pressure.
Delusion: Data from
world-wide studies strongly supports a J-shaped curve for the
association between sodium intake and health outcomes, including but
not limited to hypertension. A J-shaped curve looks like a Nike
swoosh, showing increased risk at both the low and high ends of
intake. Health risk steeply rises as dietary sodium falls below
2300 mg/day. Between 2300 and 3500 mg/day risk is low and
relatively flat, then slowly increases through 5000 mg/day. After
that risk rises more steeply with higher intakes.
In spite of this data, which has been available since the 1990’s,
the American Heart Association recommends less than 1500 mg/day for
everyone, based mostly on blood pressure studies. The World
Health Organization sets goals of less than 2000 mg/day, but couples
that with a recommendation to eat at least 3510 mg potassium per day.
We need sodium. It is essential for cellular and organ function,
energy generation, blood pressure support, nerve and muscular function
and proper kidney function. Even mildly low sodium levels can
cause weakness and problems with thinking and memory, especially in the
elderly.
Excessive sodium restriction has good reason to backfire, especially in
heart failure patients. Very low sodium intake activates a
regulatory system called RAAS, which tightly controls sodium
levels. The RAAS thinks that low sodium means low blood pressure
and the body is at risk of dying. It senses sodium intakes below
1500 mg/day and kicks in to raise blood pressure.
RAAS is great as a fail-safe mechanism to prevent death from low sodium
and blood pressure, but its persistently high activation contributes to
thickening of the heart muscle and kidney tissue. That’s
the opposite of what we should want for our heart failure patients, or
anyone else for that matter.
Very low sodium intake also increases sympathetic nervous system
activity, which raises heart rate and blood pressure. It
increases insulin resistance, accelerating the journey to overt
diabetes.
Until now the many in the science community rejected the J-shaped curve
and unhealthy effects of excessive sodium restriction as
“improbable.” It didn’t fit accepted
knowledge, so it was considered faulty. Critics emphasized the
studies’ methodological problems, without acknowledging the same
problems with the lower-sodium-is-better studies.
Desirable: In 2005 the
IOM accepted the J-shaped curve and set an “adequate
intake” recommendation of more than 1500 mg/day, but didn’t
call it a requirement. The IOM’s 2013 guidelines go a step
further, stating that very low dietary sodium is unhealthy for patients
with heart failure.
In spite of this shift by the IOM, government policy and physician
recommendations have not changed concerning very low sodium
intakes.
The presenters at the ASCN symposium, all eminent nutrition scientists,
suggested that 2300 – 4945 mg/day is OK in most people, depending
on genetics and other life-style factors. That range happens to
coincide with usual intake by the majority of societies across the
globe – both Westernized nations suffering from an epidemic of
cardiovascular disease and subsistence societies virtually free of that
scourge.
The ASCN presenters basically castigated policy makers for continuing
the lower-is-better view. They also felt that a population-wide
effort to restrict sodium intake to 2300 mg/day 1) is not supported by
the data; 2) is a misplaced use of effort and resources; and 3)
potentially increases harm when the elderly with minimal sodium intake
become weak and fall from inadequate blood levels, or zero-sodium
zealots develop unwanted cardiovascular effects of an activated
RAAS.
Cardiologists argue against policy change, fearing that deemphasizing
salt restriction will keep people from reducing it at all.
That’s a valid concern since very high sodium diets are bad for
health, especially in those whose idea of a low-sodium diet is to eat
only half the bag of chips.
Continuing to focus entirely on sodium ignores the compelling DASH and
potassium benefit. A recommendation to eat minimally processed
food diets (processed food generally has a lot of sodium), full of
vegetables, whole grains, fruits, low-fat dairy and lean animal
products focuses on all the good things, not just salt.
The taste for salt is the only taste sensation that turns both on and
off according to the body’s need. Anyone consuming a DASH
diet who craves salt should eat some.
The J-shaped curve has been around for a long time. The IOM
accepts it as valid, and they are a tough audience. Policy-makers
should heed the advice of the IOM and the implications of all the
scientific data, not just the biased data that drive their policy.