Should everyone cut back on salt? There's still no
In November 2009, an Institute of Medicine (IOM) committee held
its final information-gathering session on ways to reduce sodium
consumption in the United States. The panel will issue its
findings in a report due out in February 2010. The IOM's mission
is to bring our sodium intake down to the levels recommended by
the Dietary Guidelines for Americans (www.health.gov/DietaryGuidelines)
— namely, for the average adult, no more than 2,300 milligrams
(mg) per day, the amount in about a teaspoon of ordinary iodized
table salt. Lower consumption — no more than 1,500 mg per day,
about two-thirds of a teaspoon of salt — is recommended for
middle-aged and older adults, African Americans, and people with
high blood pressure.
Most of the sodium in our diet comes from salt, or sodium
chloride. Salt is about 40% sodium by weight. Sodium has many
important biological functions — transmitting nerve impulses,
contracting and relaxing muscle fibers, and maintaining proper
fluid balance. But Americans get much more than they need — 3,400
mg of sodium per day, on average. The kidneys regulate the body's
sodium level by getting rid of any excess. But if there's too
much sodium in the bloodstream, the kidneys can't keep up. Excess
sodium in the blood pulls out water from the cells; as this fluid
increases, so does blood volume. That means more work for the
heart, increased pressure in the blood vessels, and often,
eventually, stiffened vessel walls, chronic high blood pressure,
and an increased risk of heart attack or stroke.
Some people are especially sensitive to sodium — their blood
pressure rises and falls directly with their sodium intake. That
puts them at increased risk for cardiovascular disease, even if
they don't have high blood pressure, and it means they
particularly benefit from restricting sodium intake. Those most
prone to salt sensitivity include the elderly, African Americans,
and people with hypertension, diabetes, or chronic kidney
Sources of sodium
Sodium and the public's health
As many as one in three adults in the United States has high
blood pressure — also called hypertension, which is defined as a
reading of 140/90 millimeters of mercury (mm Hg) or higher. Many
more have "prehypertension" (a systolic blood pressure reading of
120 to 139 mm Hg or a diastolic reading of 80 to 89 mm Hg), which
means that while they don't have high blood pressure, they're
likely to develop it. Many studies have shown that blood pressure
is directly related to dietary sodium, so it makes sense for
at-risk individuals to cut back. But what about the rest of us?
The Centers for Disease Control and Prevention (CDC) says that
limiting sodium intake should be just about everyone's concern.
In a 2009 study using data from the National Health and Nutrition
Examination Surveys and referring to the Dietary Guidelines for
Americans, CDC researchers concluded that 70% of American adults
— about 145 million people, including everyone over age 40, all
African Americans, and people with hypertension — should aim for
a sodium intake of no more than 1,500 mg per day.
Some public health experts believe the 1,500-mg-per-day cap
should be extended to everyone. Others say that proposal ignores
other factors influencing blood pressure — and could have
unintended consequences (like the campaign to reduce fat
consumption by substituting carbohydrates, which has been
associated with increased obesity). Almost everyone agrees that
we couldn't reach the 1,500-mg limit without reducing the amount
of salt in processed and prepared foods — the main source of
Appearing before the IOM committee in the spring of 2009, Dr.
Frank Sacks, a professor at Harvard Medical School and the
Harvard School of Public Health, who is also vice-chair of the
American Heart Association nutrition committee, testified that
the heart association wants manufacturers and restaurants to
reduce added salt in foods by 50% by 2020, "for the benefit of
Current recommended intakes of sodium for healthy adults
by age group
Adequate intake (AI) of sodium*
Upper limit (UL) of sodium intake**
1.5 g/1,500 mg
3,800 mg, or ⅔ teaspoon (tsp.)
2.3 g/2,300 mg (equivalent to 5.8 g/5,800 mg, or 1 tsp.,
1.3 g/1,300 mg
3,200 mg, or ~½ tsp.
Less than 2.3 g, but a precise amount has not been
Ages 71 and over
1.2 g/1,200 mg
2,900 mg, or ½ tsp.
*The average amount needed to replace sodium lost daily
through sweat while providing enough other essential
**UL may be higher for people who lose large amounts of
sodium in sweat, such as athletes and workers exposed to
Source: Dietary Reference Intakes for Water,
Potassium, Sodium, Chloride, and Sulfate, National
Academies Press (2004).
Reduction or restriction?
Many studies have investigated links between sodium intake, blood
pressure, and cardiovascular disease. Some of the most compelling
evidence has come from the Dietary Approaches to Stop
Hypertension (DASH) trials.
The first DASH trial showed that a diet rich in fruits,
vegetables, low-fat dairy products, whole grains, beans, nuts,
fish, lean meats, and poultry lowered blood pressure. In a
follow-up trial, this diet was compared with one closely
resembling the average American diet, and both diets were further
divided into three sodium levels: high (3,500 mg/day), moderate
(2,400 mg/day), and low (1,500 mg/day). More than 400 volunteers
followed their assigned diets for 12 weeks, changing their sodium
intake every four weeks.
Across the board, less sodium intake led to lower blood pressure.
The DASH diet with sodium restricted to just 1,500 mg per day
worked best for all participants, and for people with
hypertension, it was almost as effective as medication.
The researchers concluded that we could all benefit from reducing
our sodium intake. But the study did little to quell controversy
over the issue. Critics charged that it was too brief to justify
a general recommendation, and they warned of health risks from
insufficient sodium in the diet. Proponents say that's unlikely,
because most human beings don't even need as much as 1,500 mg a
day for good health. Of course, this 12-week study couldn't
predict the impact of reduced sodium intake on the risk of
cardiovascular disease down the road.
A 2007 follow-up study of the Trials of Hypertension Prevention
(TOHP) provided a longer-term perspective. The original TOHP
study involved two randomized trials of lifestyle interventions
conducted in the late 1980s and early 1990s. A team led by
Harvard researchers tracked down the original TOHP participants
and found that those who had permanently lowered their sodium
intake to between 2,000 and 2,600 mg per day and continued to
watch their salt intake had almost 30% fewer cardiovascular
events, including death, in the following 10 to 15 years. The
TOHP trials didn't require drastic dietary changes. Instead, the
volunteers learned how to look out for hidden salt and avoid it;
those who were able to reduce their salt intake by one-third to
one-half teaspoon per day reaped the cardiovascular benefits.
So it's unclear whether these results mean we should reduce
sodium intake to no more than 1,500 mg per day or ask food
processors and purveyors to cut added salt by half.
The controversy about universal salt restriction will probably
continue. As in most health matters, one size doesn't fit all.
How salt affects your blood pressure and health depends on many
things, including your genes, age, race, and medical conditions.
Nevertheless, policy makers are likely to sit up and take notice
of an analysis from the RAND Corporation, a nonprofit research
organization. According to the study, published in the
American Journal of Health Promotion (September/October
2009), lowering Americans' sodium consumption to less than 2,300
mg per day could result in 11 million fewer cases of high blood
pressure. The savings could amount to as much as $18 billion
annually in health care costs — and further reductions might
yield even greater savings.
What about iodine?
Iodine is essential to human life. Too little can result
in serious health problems, including thyroid enlargement
(goiter) and neurological difficulties. Most of the
iodine we need comes from iodized salt. Five grams of
iodized salt (close to a teaspoon) meets the Institute of
Medicine's 150-microgram (mcg) recommended daily intake
of iodine for nonpregnant adults.
Would long-term salt restriction — or the use of
non-iodized gourmet salts and kosher salt — result in
insufficient iodine intake? So far, this hasn't been the
object of concerted scientific study. The National Health
and Nutrition Examination Surveys did report a sharp
decline in average iodine intake between the early 1970s
and the 1990s, but it never fell below the level needed
for good health and is now on the increase again.
People cutting back on iodized salt can find other food
sources of iodine. One of the best is seaweed (kelp,
wakame, nori). Another is seafood (clams, oysters,
lobster, shrimp, sardines, and ocean fish). Wherever
iodine is added to animal feed, dairy products are a good
source. Some breads also contain significant amounts of
iodine. Unfortunately, iodine content isn't listed in the
Nutrition Facts label. Fruits and vegetables contain
iodine, but they're typically not a concentrated source,
and the amount depends in part on the soil they're grown
in and the fertilizers applied to them. Apart from
iodized salt, the most reliable source of iodine is
probably an iodine-containing multivitamin.
What to do
If you're under age 50, your blood pressure is in the healthy
range (under 120/80 mm Hg), and your health is good, you have
little reason to worry about your dietary sodium intake, at least
for now. Still, try to limit it to no more than 2,300 mg per day.
The risk for high blood pressure rises with age, so you'll do
yourself a favor if you wean your taste buds from a yen for salt.
Research has shown that people who slowly reduce their intake
find that they eventually prefer less salt. Many older, obese, or
diabetic people and African Americans are salt-sensitive, and
most experts agree that they should cut back. For them, as well
as for people with hypertension, prehypertension, kidney disease,
or heart failure, sodium intake should be less than 1,500 mg a
If you're hypertensive or prehypertensive or just want a healthy
eating plan, consider following one of the three diets that were
tested in the OmniHeart trial: the DASH-like diet (/148) and two others, one high
in unsaturated fats and the other high in protein (www.omniheart.org). Results
published in The Journal of the American Medical
Association (Nov. 16, 2005) showed that all three diets
lowered blood pressure, improved cholesterol levels, and reduced
the risk of heart disease. (The high-unsaturated-fat and
high-protein diets improved cholesterol levels and blood pressure
even more than the DASH diet, which was higher in carbohydrates.)
The health benefits of these eating plans can't be attributed to
any single ingredient — the magic is probably in the mix — but
one reason they work is that they're rich in potassium. So
whatever diet you follow, make sure it includes plenty of fruits
and vegetables, which contain little or no sodium and are an
important source of potassium. Potassium-rich choices include
bananas, orange juice, cantaloupe, spinach, avocado, and sweet
Here are some ways to reduce your sodium intake:
Eat mostly fresh foods. Most of the
sodium we eat comes from restaurant meals and processed foods,
including canned vegetables and soups, pasta sauces, frozen
entrees, luncheon meats, and snack foods. If you start with
unsalted, fresh foods and prepare them yourself, you can exercise
better control over your sodium intake.
Take care with condiments. Sodium is
found in many condiments besides ordinary table salt — including
soy sauce, Worcestershire sauce, salad dressings, ketchup,
seasoned salts, pickles, and olives. Baking soda, baking powder,
and monosodium glutamate (MSG) also contain sodium.
Read labels. The Nutrition Facts label
on packaged food lists milligrams of sodium per serving, so note
how many servings the container holds. The percent daily value
("% Daily Value" or "% DV") is based on 2,400 mg, so if your own
daily sodium limit is lower, the amount of sodium in a serving is
actually a higher percentage than the label indicates. Read the
labels on over-the-counter drugs, too; some of them contain
Speak up. When dining out, ask to have
your food prepared with less salt. You can also ask for a lemon
or lime wedge to add more flavor to your food.
Spice it up. Cut back on salt by making
your own blends of spices and herbs and using them along with
lemon or lime juice or flavored vinegars. (Ready-made blends are
also available in grocery stores.) Some kosher and gourmet salts
contain less sodium than standard iodized table salt; check the
Nutrition Facts label to make sure.
As a service to our readers, Harvard Health Publishing provides access to our library of archived content.
Please note the date of last review or update on all articles. No content on this site, regardless of date,
should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.