is essential to the functioning of every cell in
our bodies. Compounds containing sodium
and potassium are electrolytes, substances
that dissolve in water and produce ions. The
resulting solution conducts an electric current.
In the human body, many processes require
electrical signals for communication, especially
in the nervous system, brain, and muscles. For
example, sodium ions are necessary to gener-
ate those electrical signals. Too much sodium,
or too little, can cause cells to malfunction
(Fig. 1) and, if taken to an extreme, can be fatal.
Sodium is the major positive ion in bodily
fluids, so its concentration determines the
total concentration of solutes—called the
osmolarity—in these fluids. When two fluids
with different osmolarities are separated by a
membrane, then water tends to flow through
the membrane to equalize the concentrations.
Through a process called osmosis (Fig. 2),
water moves across the semipermeable mem-
brane from an area of low-solute concentra-
tion to an area of high-solute concentration.
In the case of bodily fluids, the fluid inside
cells is separated from the fluid in the blood.
So, if the osmolarity of blood is not balanced
with the osmolarity inside cells, the total
volume of liquid in the cells may increase or
decrease. Without enough sodium, cells in our
bodies would lose water, causing dehydration,
low blood pressure, and possibly death.
Salt is excreted through urine and through
sweat. Because salt is excreted from the body,
it must be constantly replaced. However, most
people choose to continue eating salt, even
when their needs have been met. Could people
benefit from consuming higher levels of salt
for reasons scientists do not yet understand?
Some researchers suggest that high-salt
consumption is merely a habit learned in
childhood or, possibly, an addiction. Others
suggest that evolution has given people a
taste preference for salt, even when they do
not need it.
How much salt do
If you are athletic and eat a low-salt diet, you
may be getting too little salt. However, if you
eat a lot of processed foods, you may be getting more salt than you need. As is probably
clear to you by now, scientists and the medical
community have not yet agreed on the optimal
amount of salt people should get, but for most
people, moderation is a good option.
You can estimate your daily intake of salt
by paying attention to the nutrition labels on
food. Some foods, including ready-to-eat
foods such as items from the deli or bakery,
are not required to have nutrition labels. If you
eat a lot of these foods, or a lot of restaurant
foods, it is harder to estimate your salt intake.
However, you can look online for nutrition
information for many restaurants, and deli and
bakery items. Search for “nutrition informa-
( www.myfitnesspal.com) also offers a free
mobile app, and the online site lists nutrition
information for thousands of products.
Blood tests can confirm your blood sodium
level. If you discover that you eat too much
salt, try to cut back on high-salt foods or add
little or no salt to your food at the table. If
food lacks flavor, you can try adding spices or
Zaraska, M. Pass the Salt, Please. It’s Good for You.
The Washington Post, May 4, 2015: http://wpo.
st/GFtG0 [accessed Nov 2015].
Ballantyne, C. Strange but True: Drinking Too Much
Water Can Kill. Scientific American, June 21,
article/strange-but-true-drinking-too-much-water-can-kill/ [accessed Nov 2015].
Sodium (Na) in Blood. WebMD, Sept 9, 2014:
sodium-na-in-blood [accessed Nov 2015].
Chris Eboch is a science writer who lives in
Socorro, N.M. Her most recent ChemMatters
article, “Geothermal Power: Hot Stuff,” appeared in
the December 2015/January 2016 issue.
Figure 1. Compared to normal cells (a), cells that contain too little salt (b) lose water, and cells
that contain too much salt (c) draw in more water than they can sustain (and may burst).
ChemMatters | FEBRUARY/MARCH 2016 13
Ions Sodium Ions
77% from packaged
and restaurant food.
12% from foods that
contain sodium naturally.
11% from adding salt
to food while cooking or
at the table.
membrane same concentration of sugar on
both sides of semipermeable
Figure 2. Osmosis is the spontaneous movement of solvent (here, water) molecules through a semi-
permeable membrane from a region of low concentration of solute (here, sugar) molecules. The end
result is that the solute concentrations are the same on both sides of the semipermeable membrane.