Looks can be
You can see the salt on
potato chips, but break-
fast cereals, spaghetti
sauce, and frozen dinners
also contain salt.
Randomized controlled trials
Ideally, participants are randomly divided into two groups. An experimental group receives treatment; a control group does not. This type of
study, called a randomized controlled trial, is considered the most reliable
Short-term randomized controlled trials, involving a few hundred
patients studied over several weeks, have shown a link between high salt
intake and high blood pressure. But such studies have not directly linked
high salt intake to health problems, such as heart attacks and strokes.
A better diet study might randomly assign test subjects meals with different amounts of sodium and then record their rate of health problems,
such as heart attacks and strokes.
But to get definite results, such a
study would have to use thousands
of patients over several years, which
is impossible in a clinical setting.
Just How Much Salt Do We Need?
What can be
To lift the uncertainty over how
much salt we need in our diet, more
studies of both types, clinical and
observational, are needed. Long-term
clinical studies would be ideal but are diffi-
cult to conduct. Observational studies that
follow large populations for years may pro-
vide more data. Ideally these would also
study how changing sodium intake affects
health, and how sodium intake affects
people with different health conditions.
What will you do?
For now, expert opinions are divided.
However, you still need to make
informed choices about your own
sodium consumption. How will
you decide how much salt you
need? What information will you
use to make that choice?
In an observational study, scientists track normal behavior rather than trying to control it. For example, starting in 2003, scientists studied the
sodium intake of more than 100,000 people from 17 countries.
The test subjects each provided a urine sample. These showed how much
sodium and potassium were eliminated by their bodies, a good estimate of
sodium intake. The test subjects then ate their usual diet, and the study recorded
major cardiovascular events, such as heart attacks and strokes, as well as death
rates, over the course of 10 years.
The study found that people with the highest levels of sodium had a 15%
increase in the risk of death or major cardiovascular event. The highest risk
was for people with unusually high blood pressure, or hypertension. However,
the study also found that people with the lowest sodium intake had a 27%
increase in risk. People who met the low U.S. recommended limits for salt
( 2,300 milligrams of sodium per day) had more heart trouble than those
consuming moderate amounts of salt. But the test subjects may have other
behaviors that would cause health problems, making it difficult to identify
what is causing the problem.
In the end, the two different types of studies—randomized controlled trials and
observational studies—have produced contradictory results.
SOME SCIENTISTS AND DOCTORS SAY WE SHOULD LIMIT OUR salt intake. Other experts believe a higher salt intake is fine,
and maybe even healthier. Why is there so much debate about how
much salt we need in our diet? The main reason is that it is difficult
to conduct long-term studies of diet.
www.acs.org/chemmatters 4 ChemMatters | FEBRUARY/MARCH 2016
By Chris Eboch