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 Researchers found that athletes who lost fluid equal to 2 percent
their weight took a hit to their cognition. Even this mild to
moderate level of dehydration- the loss of 2 pounds for someone who
weighs 100 pounds and four pounds for someone weighing 200 - led to
attention problems and impaired decision making, according to the
report in Medicine & Science in Sports & Exercise.
In particular, dehydration led to impairment in tasks requiring
attention, motor coordination, and so-called executive function,
which includes things like map recognition, grammatical reasoning,
mental math, and proofreading, for example.
"We've known that physical performance suffers at a threshold of 2
percent of body mass, particularly when it's from exercise in a warm
environment," said study coauthor Mindy Millard-Stafford, a
professor in the school of biological sciences and director of the
physiology lab at the Georgia Institute of Technology.
"So the question was, what happens in the brain with the same amount
of loss, which is pretty common with people who are active or work
outside in the heat. Just like a muscle cell needs water, so do the
cells in our brain."
While the effects weren't huge at 2 percent, they increased with
increasing dehydration, Millard-Stafford said.
The new study isn't the first to look at the impact of dehydration
on cognition. But earlier research yielded mixed findings, possibly
because studies were based on small numbers of subjects.
Millard-Stafford decided to get around that pitfall by performing a
meta-analysis, an approach that combines data from many smaller
studies.
After scouring the medical literature, the researchers found 33
studies involving a total of 413 adults. Participants lost fluids
amounting to 1 to 6 percent of their body mass either through
exercise alone, exercise coupled with heat, heat alone or fluid
restriction.
The study may be particularly timely as much of the country suffers
through a heat wave. And it may remind weekend warriors as well as
more dedicated athletes of the importance of staying hydrated.
"I think this reinforces something we thought was true," said Dr.
Ronald Roth, a professor of emergency medicine at the University of
Pittsburgh School of Medicine, medical director of the Dick's
Sporting Goods-Pittsburgh Marathon and one of the team physicians
for the Pittsburgh Steelers. "The big picture here is that the more
dehydrated you are the less sharp you are. And your decision-making
abilities get lost sooner than later."
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Before this new research came along, a person might have happened
upon one of the earlier studies that found no cognitive effects from
dehydration and thought that dehydration wouldn't harm their
thinking, Roth said.
"As a meta-analysis, this study is bigger and more helpful than the
earlier individual studies," said Roth, who is unaffiliated with the
new research. "With a bigger pool of patients, you can get more
robust information."
It can be hard to diagnose dehydration, so it's important for
individual athletes to keep track of how much fluid they're taking
in and how much they've lost, Roth said. Still, certain symptoms
should be reminders that it's time to take in more fluid: fatigue,
muscle weakness, decreased urine output, confusion.
The Pittsburgh doctor also recommends that on especially hot days,
athletes make a plan before working out so potentially clouded
judgment won't steer them wrong.
Roth warns against overdoing things and taking in too much water,
which can lead to a dangerous condition known as hyponatremia. That
condition occurs when there's too much water compared to the amount
of salt in the body.
"It's important to know the right water balance," Millard-Stafford
concurred. "You need to know that you can have not just too little
but also too much."
The color of your urine is a simple way of monitoring your fluid
levels, Millard-Stafford said. "If it's very, very clear, then you
are probably drinking far more than necessary," she explained. "But
if it's dark gold that may mean the kidneys need a little more
reserve since they're concentrating your urine to keep the balance
where it needs to be."
SOURCE: http://bit.ly/2u7BSAI Medicine & Science in Sports &
Exercise, online June 21, 2018.
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