ChemMatters | OC TOBER/NOVEMBER 2017 7
phospholipid water molecule negative ion positive ion
Drinking a lot of water results
in a low-electrolyte
the cell relative to
Water passes through the
membrane into the cell,
diluting the electrolyte,
causing the cell to swell.
The cell membrane is
to excessive sweating, the body tries to keep
the normal Na+ level in blood between 0.135
M and 0.145 M. But when the sodium level
in blood falls below 0.135 M, hyponatremia
can occur. If an already severely dehydrated
person drinks too much water, osmosis
causes too much water to move into the cells’
When hyponatremia occurs in brain cells,
the swelling leads to increased pressure in
the skull. This can cause a series of symptoms—including headache, nausea, seizures,
respiratory arrest, and accumulation of fluid
in the lung, which can be fatal if not immediately treated.
This is probably what happened to Zyrees
and Cynthia. To stay hydrated, they drank too
much water. In doing so, they both diluted
the Na+ concentration in their blood. Through
osmosis, too much water rushed into their
brain cells when the electrolyte balance in
their bodies was stressed by excess water. All
of this led to catastrophic consequences. We
need water, but too much of it can be fatal.
Moderation is key
Sports drinks and electrolyte supplements
are probably safe if consumed in moderate
amounts, but do they help? The National
Institutes of Health (NIH) says they do, and
recommends that athletes use them to prevent hyponatremia. It seems that these athletes had the right idea, but went too far.
It’s important to stay hydrated when exer-
cising, particularly in hot weather. Many exer-
cise professionals caution that thirst is not
a good indicator of dehydration because we
often become dehydrated before we become
thirsty during exercise; however, others sug-
gest that thirst is a good indicator for most
athletes. Always drink water before, during,
Stay attentive for signs of dehydration—
nausea, muscle weakness, dizziness, and con-
fusion are all signs that something is wrong.
It could be dehydration or it could be hypona-
Substances that separate
into ions when dissolved in
water are called electrolytes.
The resulting solution
conducts electricity, due to
the mobility of the positive
and negative ions.
tremia—the symptoms are identical, so get
out of the heat and seek medical attention if
you feel these symptoms coming on.
Seen At 11: Deadly Dangers of Drinking too Much
Water. CBS News, June 10, 2015: http://newyork.
ing-too-much-water/ [accessed Aug 2017].
Kraft, A. Avoid Dangerous Over-Hydration this
Summer. CBS News, June 30, 2015: http://www.
cbsnews.com/news/avoid-dangerous-over-hydra-tion-this-summer/ [accessed Aug 2017].
Hyponatremia: Causes. Mayo Clinic, May 28, 2014:
[accessed Aug 2017].
Low Sodium Level. Medline Plus, U.S. National
Library of Medicine, June 5, 2017: https://www.
[accessed Aug 2017].
Water in Diet. Medline Plus, U.S. National Library
of Medicine, July 14, 2015: https://medlineplus.
gov/ency/article/ 002471.htm [accessed Aug 2017].
Bray, G. A, Popkin, B. M. Calorie-Sweetened
Beverages and Fructose: What Have We Learned
10 Years Later. Pediatric Obesity, Aug 2013;
8 ( 4),
Raima Larter was Professor and Chair of the
Chemistry Department at Indiana University–
Purdue University at Indianapolis, prior to serving
as Program Director in the Chemistry Division
at the National Science Foundation. She is
retired from both positions and is now a science
writer in Arlington, Va. This is her first article in
Figure 2. As a result of osmosis in a cell, water moves through a semipermeable membrane from an
area with a low-electrolyte concentration to an area with a high-electrolyte concentration. This figure
shows relative concentrations of electrolytes in the cell before and while drinking a lot of water. The
intracellular and extracellular regions will eventually have equal electrolyte concentration, or reach
equilibrium, so if excess water is consumed, equilibrium will re-establish itself through continued